text: /* Copyright (c) 2017 - 2021 LiteSpeed Technologies Inc.  See LICENSE. */
  #define _GNU_SOURCE         /* for memmem */
  
  #include <assert.h>
  #include <errno.h>
  #include <limits.h>
  #include <time.h>
  #include <string.h>
  #include <sys/queue.h>
  #ifndef WIN32
  #include <netinet/in.h>
  #include <netdb.h>
  #include <sys/socket.h>
  #else
  #include <malloc.h>
  #endif
  
  #include <openssl/ssl.h>
  #include <openssl/crypto.h>
  #include <openssl/stack.h>
  #include <openssl/x509.h>
  #include <openssl/rand.h>
  #include <openssl/nid.h>
  #include <openssl/bn.h>
  #include <openssl/hkdf.h>
  #include <zlib.h>
  
  #include "lsquic.h"
  #include "lsquic_types.h"
  #include "lsquic_crypto.h"
  #include "lsquic_str.h"
  #include "lsquic_enc_sess.h"
  #include "lsquic_parse.h"
  #include "lsquic_crt_compress.h"
  #include "lsquic_util.h"
  #include "lsquic_version.h"
  #include "lsquic_mm.h"
  #include "lsquic_engine_public.h"
  #include "lsquic_hash.h"
  #include "lsquic_qtags.h"
  #include "lsquic_byteswap.h"
  #include "lsquic_sizes.h"
  #include "lsquic_tokgen.h"
  #include "lsquic_conn.h"
  #include "lsquic_packet_common.h"
  #include "lsquic_packet_out.h"
  #include "lsquic_packet_in.h"
  #include "lsquic_handshake.h"
  #include "lsquic_hkdf.h"
  #include "lsquic_packet_ietf.h"
  
  #if __GNUC__
  #   define UNLIKELY(cond) __builtin_expect(cond, 0)
  #else
  #   define UNLIKELY(cond) cond
  #endif
  
  #include "fiu-local.h"
  
  #include "lsquic_ev_log.h"
  
  #define MIN_CHLO_SIZE 1024
  
  #define MAX_SCFG_LENGTH 512
  #define MAX_SPUBS_LENGTH 32
  
  #define LSQUIC_LOGGER_MODULE LSQLM_HANDSHAKE
  #define LSQUIC_LOG_CONN_ID lsquic_conn_log_cid(                         \
      enc_session && enc_session->es_conn     ? enc_session->es_conn :    \
      lconn && lconn != &dummy_lsquic_conn    ? lconn :                   \
                                                &dummy_lsquic_conn)
  #include "lsquic_logger.h"
  
  /* enc_session may be NULL when encrypt and decrypt packet functions are
   * called.  This is a workaround.
   */
  static struct conn_cid_elem dummy_cce;
  static const struct lsquic_conn dummy_lsquic_conn = { .cn_cces = &dummy_cce, };
  static const struct lsquic_conn *const lconn = &dummy_lsquic_conn;
  
  static int s_ccrt_idx;
  
  static const int s_log_seal_and_open;
  static char s_str[0x1000];
  
  static const unsigned char salt_Q050[] = {
      0x50, 0x45, 0x74, 0xEF, 0xD0, 0x66, 0xFE, 0x2F, 0x9D, 0x94,
      0x5C, 0xFC, 0xDB, 0xD3, 0xA7, 0xF0, 0xD3, 0xB5, 0x6B, 0x45,
  };
  
  enum handshake_state
  {
      HSK_CHLO_REJ = 0,
      HSK_SHLO,
      HSK_COMPLETED,
      N_HSK_STATES
  };
  
  #if LSQUIC_KEEP_ENC_SESS_HISTORY
  typedef unsigned char eshist_idx_t;
  
  enum enc_sess_history_event
  {
      ESHE_EMPTY              =  '\0',
      ESHE_SET_SNI            =  'I',
      ESHE_SET_SNO            =  'O',
      ESHE_SET_STK            =  'K',
      ESHE_SET_SCID           =  'D',
      ESHE_SET_PROF           =  'P',
      ESHE_SET_SRST           =  'S',
      ESHE_VSTK_OK            =  'V',
      ESHE_VSTK_FAILED        =  'W',
      ESHE_SNI_FAIL           =  'J',
      ESHE_HAS_SSTK           =  'H',
      ESHE_UNKNOWN_CONFIG     =  'a',
      ESHE_MISSING_SCID       =  'b',
      ESHE_EMPTY_CCRT         =  'c',
      ESHE_MISSING_SNO        =  'd',
      ESHE_SNO_MISMATCH       =  'e',
      ESHE_SNO_OK             =  'f',
      ESHE_MULTI2_2BITS       =  'i',
      ESHE_SNI_DELAYED        =  'Y',
  };
  #endif
  
  
  typedef struct hs_ctx_st
  {
      enum {
          HSET_TCID     =   (1 << 0),     /* tcid is set */
          HSET_SMHL     =   (1 << 1),     /* smhl is set */
          HSET_SCID     =   (1 << 2),
          HSET_IRTT     =   (1 << 3),
          HSET_SRST     =   (1 << 4),
      }           set;
      enum {
          HOPT_NSTP     =   (1 << 0),     /* NSTP option present in COPT */
          HOPT_SREJ     =   (1 << 1),     /* SREJ option present in COPT */
      }           opts;
      uint32_t    pdmd;
      uint32_t    aead;
      uint32_t    kexs;
      
      uint32_t    mids;
      uint32_t    scls;
      uint32_t    cfcw;
      uint32_t    sfcw;
      uint32_t    smids;
      uint32_t    scfcw;
      uint32_t    ssfcw;
      uint32_t    icsl;
      
      uint32_t    irtt;
      uint64_t    rcid;
      uint32_t    tcid;
      uint32_t    smhl;
      uint64_t    sttl;
      unsigned char scid[SCID_LENGTH];
      //unsigned char chlo_hash[32]; //SHA256 HASH of CHLO
      unsigned char nonc[DNONC_LENGTH]; /* 4 tm, 8 orbit ---> REJ, 20 rand */
      unsigned char  pubs[32];
      unsigned char srst[SRST_LENGTH];
      
      uint32_t    rrej;
      struct lsquic_str ccs;
      struct lsquic_str uaid;
      struct lsquic_str sni;   /* 0 rtt */
      struct lsquic_str ccrt;
      struct lsquic_str stk;
      struct lsquic_str sno;
      struct lsquic_str prof;
      
      struct lsquic_str csct;
      struct compressed_cert *ccert;
      struct lsquic_str scfg_pubs; /* Need to copy PUBS, as KEXS comes after it */
  } hs_ctx_t;
  
  
  /* client side need to store 0rtt info per STK */
  typedef struct lsquic_session_cache_info_st
  {
      unsigned char   sscid[SCID_LENGTH];
      unsigned char   spubs[32];  /* server pub key for next time 0rtt */
      uint32_t    ver;  /* one VERSION */
      uint32_t    aead;
      uint32_t    kexs;
      uint32_t    pdmd;
      uint64_t    orbt;
      uint64_t    expy;
      int         scfg_flag; /* 0, no-init, 1, no parse, 2, parsed */
      struct lsquic_str    sstk;
      struct lsquic_str    scfg;
      struct lsquic_str    sni_key;   /* This is only used as key */
      struct lsquic_hash_elem hash_el;
  
  } lsquic_session_cache_info_t;
  
  
  /* client */
  typedef struct c_cert_item_st
  {
      struct lsquic_str*  crts;
      struct lsquic_str*  hashs;
      int                 count;
  } c_cert_item_t;
  
  
  struct lsquic_sess_resume_storage
  {
      uint32_t    quic_version_tag;
      uint32_t    serializer_version;
      uint32_t    ver;
      uint32_t    aead;
      uint32_t    kexs;
      uint32_t    pdmd;
      uint64_t    orbt;
      uint64_t    expy;
      uint64_t    sstk_len;
      uint64_t    scfg_len;
      uint64_t    scfg_flag;
      uint8_t     sstk[STK_LENGTH];
      uint8_t     scfg[MAX_SCFG_LENGTH];
      uint8_t     sscid[SCID_LENGTH];
      uint8_t     spubs[MAX_SPUBS_LENGTH];
      uint32_t    cert_count;
  };
  
  
  
  
  /* gQUIC crypto has three crypto levels. */
  enum gel { GEL_CLEAR, GEL_EARLY, GEL_FORW, N_GELS /* Angels! */ };
  
  #define MAX(a, b) ((a) > (b) ? (a) : (b))
  #define IQUIC_IV_LEN 12
  #define IQUIC_HP_LEN 16
  #define MAX_IV_LEN MAX(aes128_iv_len, IQUIC_IV_LEN)
  
  struct lsquic_enc_session
  {
      struct lsquic_conn  *es_conn;
      enum handshake_state hsk_state;
      enum {
          ES_SERVER =     1 << 0,
          ES_RECV_REJ =   1 << 1,
          ES_RECV_SREJ =  1 << 2,
          ES_FREE_CERT_PTR = 1 << 3,
          ES_LOG_SECRETS   = 1 << 4,
          ES_GQUIC2        = 1 << 5,
      }                    es_flags;
      
      uint8_t have_key; /* 0, no 1, I, 2, D, 3, F */
      uint8_t peer_have_final_key;
      uint8_t server_start_use_final_key; 
  
      lsquic_cid_t cid;
      unsigned char priv_key[32];
  
      /* Have to save the initial key for diversification need */
      unsigned char enc_key_i[aes128_key_len];
      unsigned char dec_key_i[aes128_key_len];
  
  #define enc_ctx_i es_aead_ctxs[GEL_EARLY][0]
  #define dec_ctx_i es_aead_ctxs[GEL_EARLY][1]
  #define enc_ctx_f es_aead_ctxs[GEL_FORW][0]
  #define dec_ctx_f es_aead_ctxs[GEL_FORW][1]
      EVP_AEAD_CTX    *es_aead_ctxs[N_GELS][2];
  
  #define enc_key_nonce_i es_ivs[GEL_EARLY][0]
  #define dec_key_nonce_i es_ivs[GEL_EARLY][1]
  #define enc_key_nonce_f es_ivs[GEL_FORW][0]
  #define dec_key_nonce_f es_ivs[GEL_FORW][1]
      unsigned char    es_ivs[N_GELS][2][MAX_IV_LEN];
  
      unsigned char    es_hps[N_GELS][2][IQUIC_HP_LEN];
  
      hs_ctx_t hs_ctx;
      lsquic_session_cache_info_t *info;
      c_cert_item_t *cert_item;
      lsquic_server_config_t *server_config;
      SSL_CTX *  ssl_ctx;
      struct lsquic_engine_public *enpub;
      struct lsquic_str * cert_ptr; /* pointer to the leaf cert of the server, not real copy */
      struct lsquic_str   chlo; /* real copy of CHLO message */
      struct lsquic_str   sstk;
      struct lsquic_str   ssno;
  
  #if LSQUIC_KEEP_ENC_SESS_HISTORY
      eshist_idx_t        es_hist_idx;
      unsigned char       es_hist_buf[1 << ESHIST_BITS];
  #endif
      /* The remaining fields in the struct are used for Q050+ crypto */
      lsquic_packno_t             es_max_packno;
  };
  
  
  
  /* server side */
  typedef struct compress_cert_hash_item_st
  {
      struct lsquic_str*   domain; /*with port, such as "xyz.com:8088" as the key */
      struct lsquic_str*   crts_compress_buf;
      struct lsquic_hash_elem hash_el;
      
  } compress_cert_hash_item_t;
  
  /* server side, only one cert */
  typedef struct cert_item_st
  {
      struct lsquic_str*      crt;
      struct lsquic_hash_elem hash_el;
      unsigned char           key[0];
  } cert_item_t;
  
  /* server */
  static cert_item_t* find_cert(struct lsquic_engine_public *, const unsigned char *, size_t);
  static void s_free_cert_hash_item(cert_item_t *item);
  static cert_item_t* insert_cert(struct lsquic_engine_public *,
          const unsigned char *key, size_t key_sz, const struct lsquic_str *crt);
  
  #ifdef NDEBUG
  static
  enum hsk_failure_reason
  lsquic_verify_stk (enc_session_t *,
                 const struct sockaddr *ip_addr, uint64_t tm, lsquic_str_t *stk);
  
  static
  #endif
  void lsquic_gen_stk(lsquic_server_config_t *, const struct sockaddr *, uint64_t tm,
               unsigned char stk_out[STK_LENGTH]);
  
  /* client */
  static c_cert_item_t *make_c_cert_item(struct lsquic_str **certs, int count);
  static void free_c_cert_item(c_cert_item_t *item);
  
  static int get_tag_val_u32 (unsigned char *v, int len, uint32_t *val);
  static uint32_t get_tag_value_i32(unsigned char *, int);
  static uint64_t get_tag_value_i64(unsigned char *, int);
  
  static void determine_keys(struct lsquic_enc_session *enc_session);
  
  static void put_compressed_cert (struct compressed_cert *);
  
  
  #if LSQUIC_KEEP_ENC_SESS_HISTORY
  static void
  eshist_append (struct lsquic_enc_session *enc_session,
                                          enum enc_sess_history_event eh_event)
  {
      enc_session->es_hist_buf[
                      ESHIST_MASK & enc_session->es_hist_idx++ ] = eh_event;
  }
  
  
  #   define ESHIST_APPEND(sess, event) eshist_append(sess, event)
  #else
  #   define ESHIST_APPEND(sess, event) do { } while (0)
  #endif
  
  
  static void
  free_compressed_cert (void *parent, void *ptr, CRYPTO_EX_DATA *ad,
                              int index, long argl, void *argp)
  {
      put_compressed_cert(ptr);
  }
  
  
  static int
  lsquic_handshake_init(int flags)
  {
      lsquic_crypto_init();
      if (flags & LSQUIC_GLOBAL_SERVER)
      {
          s_ccrt_idx = SSL_CTX_get_ex_new_index(0, NULL, NULL, NULL,
                                                          free_compressed_cert);
          if (s_ccrt_idx < 0)
              return -1;
      }
      return lsquic_crt_init();
  }
  
  
  void
  lsquic_cleanup_gquic_crypto (struct lsquic_engine_public *enpub)
  {
      struct lsquic_hash_elem *el;
      if (enpub->enp_compressed_server_certs)
      {
          for (el = lsquic_hash_first(enpub->enp_compressed_server_certs); el;
                          el = lsquic_hash_next(enpub->enp_compressed_server_certs))
          {
              compress_cert_hash_item_t *item = lsquic_hashelem_getdata(el);
              lsquic_str_delete(item->domain);
              lsquic_str_delete(item->crts_compress_buf);
              free(item);
          }
          lsquic_hash_destroy(enpub->enp_compressed_server_certs);
          enpub->enp_compressed_server_certs = NULL;
      }
  
      if (enpub->enp_server_certs)
      {
          for (el = lsquic_hash_first(enpub->enp_server_certs); el;
                                      el = lsquic_hash_next(enpub->enp_server_certs))
          {
              s_free_cert_hash_item( lsquic_hashelem_getdata(el) );
          }
          lsquic_hash_destroy(enpub->enp_server_certs);
          enpub->enp_server_certs = NULL;
      }
  
      free(enpub->enp_server_config);
  }
  
  
  static void
  lsquic_handshake_cleanup (void)
  {
      lsquic_crt_cleanup();
  }
  
  
  int
  lsquic_init_gquic_crypto (struct lsquic_engine_public *enpub)
  {
      enpub->enp_server_config = calloc(1, sizeof(*enpub->enp_server_config));
      if (!enpub->enp_server_config)
          return -1;
  
      enpub->enp_compressed_server_certs = lsquic_hash_create();
      if (!enpub->enp_compressed_server_certs)
          return -1;
  
      enpub->enp_server_certs = lsquic_hash_create();
      if (!enpub->enp_server_certs)
      {
          lsquic_hash_destroy(enpub->enp_compressed_server_certs);
          enpub->enp_compressed_server_certs = NULL;
          return -1;
      }
  
      return 0;
  }
  
  
  /* server */
  static cert_item_t *
  find_cert (struct lsquic_engine_public *enpub, const unsigned char *key,
                                                                  size_t key_sz)
  {
      struct lsquic_hash_elem *el;
  
      if (!enpub->enp_server_certs)
          return NULL;
  
      el = lsquic_hash_find(enpub->enp_server_certs, key, key_sz);
      if (el == NULL)
          return NULL;
  
      return lsquic_hashelem_getdata(el);
  }
  
  
  /* client */
  static c_cert_item_t *
  make_c_cert_item (lsquic_str_t **certs, int count)
  {
      int i;
      uint64_t hash;
      c_cert_item_t *item = calloc(1, sizeof(*item));
      item->crts = (lsquic_str_t *)malloc(count * sizeof(lsquic_str_t));
      item->hashs = lsquic_str_new(NULL, 0);
      item->count = count;
      for (i = 0; i < count; ++i)
      {
          lsquic_str_copy(&item->crts[i], certs[i]);
          hash = lsquic_fnv1a_64((const uint8_t *)lsquic_str_cstr(certs[i]),
                          lsquic_str_len(certs[i]));
          lsquic_str_append(item->hashs, (char *)&hash, 8);
      }
      return item;
  }
  
  
  /* client */
  static void
  free_c_cert_item (c_cert_item_t *item)
  {
      int i;
      if (item)
      {
          lsquic_str_delete(item->hashs);
          for(i=0; i<item->count; ++i)
              lsquic_str_d(&item->crts[i]);
          free(item->crts);
          free(item);
      }
  }
  
  
  /* server */
  static void
  s_free_cert_hash_item (cert_item_t *item)
  {
      if (item)
      {
          lsquic_str_delete(item->crt);
          free(item);
      }
  }
  
  
  /* server */
  static cert_item_t *
  insert_cert (struct lsquic_engine_public *enpub, const unsigned char *key,
                                      size_t key_sz, const lsquic_str_t *crt)
  {
      struct lsquic_hash_elem *el;
      lsquic_str_t *crt_copy;
      cert_item_t *item;
  
      crt_copy = lsquic_str_new(lsquic_str_cstr(crt), lsquic_str_len(crt));
      if (!crt_copy)
          return NULL;
  
      item = calloc(1, sizeof(*item) + key_sz);
      if (!item)
      {
          lsquic_str_delete(crt_copy);
          return NULL;
      }
  
      item->crt = crt_copy;
      memcpy(item->key, key, key_sz);
      el = lsquic_hash_insert(enpub->enp_server_certs, item->key, key_sz,
                                                          item, &item->hash_el);
      if (el)
          return lsquic_hashelem_getdata(el);
      else
      {
          s_free_cert_hash_item(item);
          return NULL;
      }
  }
  
  
  enum rtt_deserialize_return_type
  {
      RTT_DESERIALIZE_OK              = 0,
      RTT_DESERIALIZE_BAD_QUIC_VER    = 1,
      RTT_DESERIALIZE_BAD_SERIAL_VER  = 2,
      RTT_DESERIALIZE_BAD_CERT_SIZE   = 3,
  };
  
  #define RTT_SERIALIZER_VERSION  (1 << 0)
  
  static void
  lsquic_enc_session_serialize_sess_resume(struct lsquic_sess_resume_storage *storage,
                                          enum lsquic_version version,
                                          const lsquic_session_cache_info_t *info,
                                                  const c_cert_item_t *cert_item)
  {
      uint32_t i;
      uint32_t *cert_len;
      uint8_t *cert_data;
      /*
       * assign versions
       */
      storage->quic_version_tag = lsquic_ver2tag(version);
      storage->serializer_version = RTT_SERIALIZER_VERSION;
      /*
       * server config
       */
      storage->ver = info->ver;
      storage->aead = info->aead;
      storage->kexs = info->kexs;
      storage->pdmd = info->pdmd;
      storage->orbt = info->orbt;
      storage->expy = info->expy;
      storage->sstk_len = lsquic_str_len(&info->sstk);
      storage->scfg_len = lsquic_str_len(&info->scfg);
      storage->scfg_flag = info->scfg_flag;
      memcpy(storage->sstk, lsquic_str_buf(&info->sstk), storage->sstk_len);
      memcpy(storage->scfg, lsquic_str_buf(&info->scfg), storage->scfg_len);
      memcpy(storage->sscid, &info->sscid, SCID_LENGTH);
      memcpy(storage->spubs, &info->spubs, MAX_SPUBS_LENGTH);
      /*
       * certificate chain
       */
      storage->cert_count = (uint32_t)cert_item->count;
      cert_len = (uint32_t *)(storage + 1);
      cert_data = (uint8_t *)(cert_len + 1);
      for (i = 0; i < storage->cert_count; i++)
      {
          *cert_len = lsquic_str_len(&cert_item->crts[i]);
          memcpy(cert_data, lsquic_str_buf(&cert_item->crts[i]), *cert_len);
          cert_len = (uint32_t *)(cert_data + *cert_len);
          cert_data = (uint8_t *)(cert_len + 1);
      }
  }
  
  
  #define CHECK_SPACE(need, start, end) \
      do { if ((intptr_t) (need) > ((intptr_t) (end) - (intptr_t) (start))) \
          { return RTT_DESERIALIZE_BAD_CERT_SIZE; } \
      } while (0) \
  
  static enum rtt_deserialize_return_type
  lsquic_enc_session_deserialize_sess_resume(
                                  const struct lsquic_sess_resume_storage *storage,
                                                          size_t storage_size,
                                  const struct lsquic_engine_settings *settings,
                                              lsquic_session_cache_info_t *info,
                                                      c_cert_item_t *cert_item)
  {
      enum lsquic_version ver;
      uint32_t i, len;
      uint64_t hash;
      uint32_t *cert_len;
      uint8_t *cert_data;
      void *storage_end = (uint8_t *)storage + storage_size;
      /*
       * check versions
       */
      ver = lsquic_tag2ver(storage->quic_version_tag);
      if ((int)ver == -1 || !((1 << ver) & settings->es_versions))
          return RTT_DESERIALIZE_BAD_QUIC_VER;
      if (storage->serializer_version != RTT_SERIALIZER_VERSION)
          return RTT_DESERIALIZE_BAD_SERIAL_VER;
      /*
       * server config
       */
      info->ver = storage->ver;
      info->aead = storage->aead;
      info->kexs = storage->kexs;
      info->pdmd = storage->pdmd;
      info->orbt = storage->orbt;
      info->expy = storage->expy;
      info->scfg_flag = storage->scfg_flag;
      lsquic_str_setto(&info->sstk, storage->sstk, storage->sstk_len);
      lsquic_str_setto(&info->scfg, storage->scfg, storage->scfg_len);
      memcpy(&info->sscid, storage->sscid, SCID_LENGTH);
      memcpy(&info->spubs, storage->spubs, MAX_SPUBS_LENGTH);
      /*
       * certificate chain
       */
      cert_item->count = storage->cert_count;
      cert_item->crts = malloc(cert_item->count * sizeof(lsquic_str_t));
      cert_item->hashs = lsquic_str_new(NULL, 0);
      cert_len = (uint32_t *)(storage + 1);
      for (i = 0; i < storage->cert_count; i++)
      {
          CHECK_SPACE(sizeof(uint32_t), cert_len, storage_end);
          cert_data = (uint8_t *)(cert_len + 1);
          memcpy(&len, cert_len, sizeof(len));
          CHECK_SPACE(len, cert_data, storage_end);
          lsquic_str_prealloc(&cert_item->crts[i], len);
          lsquic_str_setlen(&cert_item->crts[i], len);
          memcpy(lsquic_str_buf(&cert_item->crts[i]), cert_data, len);
          hash = lsquic_fnv1a_64((const uint8_t *)cert_data, len);
          lsquic_str_append(cert_item->hashs, (char *)&hash, 8);
          cert_len = (uint32_t *)(cert_data + len);
      }
      return RTT_DESERIALIZE_OK;
  }
  
  
  #define KEY_LABEL "quic key"
  #define KEY_LABEL_SZ (sizeof(KEY_LABEL) - 1)
  #define IV_LABEL "quic iv"
  #define IV_LABEL_SZ (sizeof(IV_LABEL) - 1)
  #define PN_LABEL "quic hp"
  #define PN_LABEL_SZ (sizeof(PN_LABEL) - 1)
  
  
  static int
  gquic2_init_crypto_ctx (struct lsquic_enc_session *enc_session,
                  unsigned idx, const unsigned char *secret, size_t secret_sz)
  {
      const EVP_MD *const md = EVP_sha256();
      const EVP_AEAD *const aead = EVP_aead_aes_128_gcm();
      unsigned char key[aes128_key_len];
      char hexbuf[sizeof(key) * 2 + 1];
  
      lsquic_qhkdf_expand(md, secret, secret_sz, KEY_LABEL, KEY_LABEL_SZ,
          key, sizeof(key));
      if (enc_session->es_flags & ES_LOG_SECRETS)
          LSQ_DEBUG("handshake key idx %u: %s", idx,
                                      HEXSTR(key, sizeof(key), hexbuf));
      lsquic_qhkdf_expand(md, secret, secret_sz, IV_LABEL, IV_LABEL_SZ,
          enc_session->es_ivs[GEL_CLEAR][idx], IQUIC_IV_LEN);
      lsquic_qhkdf_expand(md, secret, secret_sz, PN_LABEL, PN_LABEL_SZ,
          enc_session->es_hps[GEL_CLEAR][idx], IQUIC_HP_LEN);
      assert(!enc_session->es_aead_ctxs[GEL_CLEAR][idx]);
      enc_session->es_aead_ctxs[GEL_CLEAR][idx]
                  = malloc(sizeof(*enc_session->es_aead_ctxs[GEL_CLEAR][idx]));
      if (!enc_session->es_aead_ctxs[GEL_CLEAR][idx])
          return -1;
      if (!EVP_AEAD_CTX_init(enc_session->es_aead_ctxs[GEL_CLEAR][idx], aead,
                                      key, sizeof(key), IQUIC_TAG_LEN, NULL))
      {
          free(enc_session->es_aead_ctxs[GEL_CLEAR][idx]);
          enc_session->es_aead_ctxs[GEL_CLEAR][idx] = NULL;
          return -1;
      }
      return 0;
  }
  
  
  static void
  log_crypto_ctx (const struct lsquic_enc_session *enc_session,
                                      enum enc_level enc_level, int idx)
  {
      char hexbuf[EVP_MAX_MD_SIZE * 2 + 1];
  
      LSQ_DEBUG("%s keys for level %s", lsquic_enclev2str[enc_level],
          idx == 0 ? "encrypt" : "decrypt");
      LSQ_DEBUG("iv: %s",
          HEXSTR(enc_session->es_ivs[enc_level][idx], IQUIC_IV_LEN, hexbuf));
      LSQ_DEBUG("hp: %s",
          HEXSTR(enc_session->es_hps[enc_level][idx], IQUIC_HP_LEN, hexbuf));
  }
  
  
  static int
  gquic2_setup_handshake_keys (struct lsquic_enc_session *enc_session)
  {
      const unsigned char *const cid_buf = enc_session->es_conn->cn_cid.idbuf;
      const size_t cid_buf_sz = enc_session->es_conn->cn_cid.len;
      size_t hsk_secret_sz;
      int i, idx;
      const EVP_MD *const md = EVP_sha256();
      const char *const labels[] = { CLIENT_LABEL, SERVER_LABEL, };
      const size_t label_sizes[] = { CLIENT_LABEL_SZ, SERVER_LABEL_SZ, };
      const unsigned dirs[2] = {
          (enc_session->es_flags & ES_SERVER),
          !(enc_session->es_flags & ES_SERVER),
      };
      unsigned char hsk_secret[EVP_MAX_MD_SIZE];
      unsigned char secret[SHA256_DIGEST_LENGTH];
  
      if (!HKDF_extract(hsk_secret, &hsk_secret_sz, md, cid_buf, cid_buf_sz,
                                                  salt_Q050, sizeof(salt_Q050)))
      {
          LSQ_WARN("HKDF extract failed");
          return -1;
      }
  
      for (i = 0; i < 2; ++i)
      {
          idx = dirs[i];
          lsquic_qhkdf_expand(md, hsk_secret, hsk_secret_sz, labels[idx],
                      label_sizes[idx], secret, sizeof(secret));
          /*
          LSQ_DEBUG("`%s' handshake secret: %s",
              HEXSTR(secret, sizeof(secret), hexbuf));
          */
          if (0 != gquic2_init_crypto_ctx(enc_session, i,
                                                      secret, sizeof(secret)))
              goto err;
          if (enc_session->es_flags & ES_LOG_SECRETS)
              log_crypto_ctx(enc_session, ENC_LEV_CLEAR, i);
      }
  
      return 0;
  
    err:
      return -1;
  }
  
  
  static void
  maybe_log_secrets (struct lsquic_enc_session *enc_session)
  {
      const char *log;
      log = getenv("LSQUIC_LOG_SECRETS");
      if (log)
      {
          if (atoi(log))
              enc_session->es_flags |= ES_LOG_SECRETS;
          LSQ_DEBUG("will %slog secrets",
              enc_session->es_flags & ES_LOG_SECRETS ? "" : "not ");
      }
  }
  
  
  static enc_session_t *
  lsquic_enc_session_create_client (struct lsquic_conn *lconn, const char *domain,
                      lsquic_cid_t cid, struct lsquic_engine_public *enpub,
                                      const unsigned char *sess_resume, size_t sess_resume_len)
  {
      lsquic_session_cache_info_t *info;
      struct lsquic_enc_session *enc_session;
      c_cert_item_t *item;
      const struct lsquic_sess_resume_storage *sess_resume_storage;
  
      if (!domain)
      {
          errno = EINVAL;
          return NULL;
      }
  
      enc_session = calloc(1, sizeof(*enc_session));
      if (!enc_session)
          return NULL;
  
      /* have to allocate every time */
      info = calloc(1, sizeof(*info));
      if (!info)
      {
          free(enc_session);
          return NULL;
      }
  
      if (sess_resume && sess_resume_len > sizeof(struct lsquic_sess_resume_storage))
      {
          item = calloc(1, sizeof(*item));
          if (!item)
          {
              free(enc_session);
              free(info);
              return NULL;
          }
          sess_resume_storage = (const struct lsquic_sess_resume_storage *)sess_resume;
          switch (lsquic_enc_session_deserialize_sess_resume(sess_resume_storage,
                                                          sess_resume_len,
                                                          &enpub->enp_settings,
                                                          info, item))
          {
              case RTT_DESERIALIZE_BAD_QUIC_VER:
                  LSQ_ERROR("provided sess_resume has unsupported QUIC version");
                  free(item);
                  break;
              case RTT_DESERIALIZE_BAD_SERIAL_VER:
                  LSQ_ERROR("provided sess_resume has bad serializer version");
                  free(item);
                  break;
              case RTT_DESERIALIZE_BAD_CERT_SIZE:
                  LSQ_ERROR("provided sess_resume has bad cert size");
                  free(item);
                  break;
              case RTT_DESERIALIZE_OK:
                  memcpy(enc_session->hs_ctx.pubs, info->spubs, 32);
                  enc_session->cert_item = item;
                  break;
          }
      }
      enc_session->es_conn = lconn;
      enc_session->enpub = enpub;
      enc_session->cid   = cid;
      enc_session->info  = info;
      /* FIXME: allocation may fail */
      lsquic_str_append(&enc_session->hs_ctx.sni, domain, strlen(domain));
      maybe_log_secrets(enc_session);
      if (lconn->cn_version >= LSQVER_050)
      {
          enc_session->es_flags |= ES_GQUIC2;
          gquic2_setup_handshake_keys(enc_session);
      }
      return enc_session;
  }
  
  
  /* Server side: Session_cache_entry can be saved for 0rtt */
  static enc_session_t *
  lsquic_enc_session_create_server (struct lsquic_conn *lconn, lsquic_cid_t cid,
                          struct lsquic_engine_public *enpub)
  {
      fiu_return_on("handshake/new_enc_session", NULL);
  
      struct lsquic_enc_session *enc_session;
  
      enc_session = calloc(1, sizeof(*enc_session));
      if (!enc_session)
          return NULL;
  
      enc_session->es_conn = lconn;
      enc_session->enpub = enpub;
      enc_session->cid = cid;
      enc_session->es_flags |= ES_SERVER;
      maybe_log_secrets(enc_session);
      if (lconn->cn_version >= LSQVER_050)
      {
          enc_session->es_flags |= ES_GQUIC2;
          gquic2_setup_handshake_keys(enc_session);
      }
      return enc_session;
  }
  
  
  static void
  lsquic_enc_session_reset_cid (enc_session_t *enc_session_p,
                                          const lsquic_cid_t *new_cid)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
  
      LSQ_INFOC("changing CID to %"CID_FMT, CID_BITS(new_cid));
      enc_session->cid = *new_cid;
  }
  
  
  static void
  put_compressed_cert (struct compressed_cert *ccert)
  {
      if (ccert)
      {
          assert(ccert->refcnt > 0);
          --ccert->refcnt;
          if (0 == ccert->refcnt)
              free(ccert);
      }
  }
  
  
  static struct compressed_cert *
  new_compressed_cert (const unsigned char *buf, size_t len)
  {
      struct compressed_cert *ccert;
  
      ccert = malloc(sizeof(*ccert) + len);
      if (ccert)
      {
          ccert->refcnt = 1;
          ccert->len = len;
          memcpy(ccert->buf, buf, len);
      }
      return ccert;
  }
  
  
  static void
  lsquic_enc_session_destroy (enc_session_t *enc_session_p)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      enum gel gel;
      unsigned i;
  
      if (!enc_session)
          return ;
  
      hs_ctx_t *hs_ctx = &enc_session->hs_ctx;
      
      lsquic_str_d(&hs_ctx->sni);
      lsquic_str_d(&hs_ctx->ccs);
      lsquic_str_d(&hs_ctx->ccrt);
      lsquic_str_d(&hs_ctx->stk);
      lsquic_str_d(&hs_ctx->sno);
      lsquic_str_d(&hs_ctx->prof);
      lsquic_str_d(&hs_ctx->csct);
      put_compressed_cert(hs_ctx->ccert);
      hs_ctx->ccert = NULL;
      lsquic_str_d(&hs_ctx->uaid);
      lsquic_str_d(&hs_ctx->scfg_pubs);
      lsquic_str_d(&enc_session->chlo);
      lsquic_str_d(&enc_session->sstk);
      lsquic_str_d(&enc_session->ssno);
      for (gel = 0; gel < N_GELS; ++gel)
          for (i = 0; i < 2; ++i)
              if (enc_session->es_aead_ctxs[gel][i])
              {
                  EVP_AEAD_CTX_cleanup(enc_session->es_aead_ctxs[gel][i]);
                  free(enc_session->es_aead_ctxs[gel][i]);
              }
      memset(enc_session->es_aead_ctxs, 0, sizeof(enc_session->es_aead_ctxs));
      if (enc_session->info)
      {
          lsquic_str_d(&enc_session->info->sstk);
          lsquic_str_d(&enc_session->info->scfg);
          lsquic_str_d(&enc_session->info->sni_key);
          free(enc_session->info);
      }
      if (enc_session->cert_item)
      {
          free_c_cert_item(enc_session->cert_item);
          enc_session->cert_item = NULL;
      }
      if ((enc_session->es_flags & ES_FREE_CERT_PTR) && enc_session->cert_ptr)
          lsquic_str_delete(enc_session->cert_ptr);
      free(enc_session);
  
  }
  
  
  static int get_hs_state(struct lsquic_enc_session *enc_session)
  {
      return enc_session->hsk_state;
  }
  
  
  /* make sure have more room for encrypt */
  static int
  lsquic_enc_session_is_hsk_done (enc_session_t *enc_session_p)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      return (get_hs_state(enc_session) == HSK_COMPLETED);
  }
  
  
  static void
  process_copt (struct lsquic_enc_session *enc_session, const uint32_t *const opts,
                  unsigned n_opts)
  {
      unsigned i;
      for (i = 0; i < n_opts; ++i)
          switch (opts[i])
          {
          case QTAG_NSTP:
              enc_session->hs_ctx.opts |= HOPT_NSTP;
              break;
          case QTAG_SREJ:
              enc_session->hs_ctx.opts |= HOPT_SREJ;
              break;
          }
  }
  
  
  static int parse_hs_data (struct lsquic_enc_session *enc_session, uint32_t tag,
                            unsigned char *val, int len, uint32_t head_tag)
  {
      hs_ctx_t * hs_ctx = &enc_session->hs_ctx;
      int is_client = (head_tag != QTAG_CHLO);
  
      switch(tag)
      {
      case QTAG_PDMD:
          hs_ctx->pdmd = get_tag_value_i32(val, len);
          break;
  
      case QTAG_MIDS:
          if (0 != get_tag_val_u32(val, len,
                      (is_client ? &hs_ctx->mids : &hs_ctx->smids)))
              return -1;
          break;
  
      case QTAG_SCLS:
          hs_ctx->scls = get_tag_value_i32(val, len);
          break;
  
      case QTAG_CFCW:
          if (0 != get_tag_val_u32(val, len, (is_client ? &hs_ctx->cfcw : &hs_ctx->scfcw)))
              return -1;
          break;
  
      case QTAG_SFCW:
          if (0 != get_tag_val_u32(val, len, (is_client ? &hs_ctx->sfcw : &hs_ctx->ssfcw)))
              return -1;
          break;
  
      case QTAG_ICSL:
          hs_ctx->icsl = get_tag_value_i32(val, len);
          break;
  
      case QTAG_IRTT:
          if (0 != get_tag_val_u32(val, len, &hs_ctx->irtt))
              return -1;
          hs_ctx->set |= HSET_IRTT;
          break;
  
      case QTAG_COPT:
          if (0 == len % sizeof(uint32_t))
              process_copt(enc_session, (uint32_t *) val, len / sizeof(uint32_t));
          /* else ignore, following the reference implementation */
          break;
  
      case QTAG_SNI:
          lsquic_str_setto(&hs_ctx->sni, val, len);
          ESHIST_APPEND(enc_session, ESHE_SET_SNI);
          break;
  
      case QTAG_CCS:
          lsquic_str_setto(&hs_ctx->ccs, val, len);
          break;
  
      case QTAG_CCRT:
          lsquic_str_setto(&hs_ctx->ccrt, val, len);
          break;
  
      case QTAG_CRT:
          put_compressed_cert(hs_ctx->ccert);
          hs_ctx->ccert = new_compressed_cert(val, len);
          break;
  
      case QTAG_PUBS:
          if (head_tag == QTAG_SCFG)
              lsquic_str_setto(&hs_ctx->scfg_pubs, val, len);
          else if (len == 32)
              memcpy(hs_ctx->pubs, val, len);
          break;
  
      case QTAG_RCID:
          hs_ctx->rcid = get_tag_value_i64(val, len);
          break;
  
      case QTAG_UAID:
          lsquic_str_setto(&hs_ctx->uaid, val, len);
          break;
  
      case QTAG_SMHL:
          if (0 != get_tag_val_u32(val, len, &hs_ctx->smhl))
              return -1;
          hs_ctx->set |= HSET_SMHL;
          break;
  
      case QTAG_TCID:
          if (0 != get_tag_val_u32(val, len, &hs_ctx->tcid))
              return -1;
          hs_ctx->set |= HSET_TCID;
          break;
  
      case QTAG_EXPY:
          enc_session->info->expy = get_tag_value_i64(val, len);
          break;
  
      case QTAG_ORBT:
          enc_session->info->orbt = get_tag_value_i64(val, len);
          break;
  
      case QTAG_SNO:
          if (is_client)
          {
              lsquic_str_setto(&enc_session->ssno, val, len);
          }
          else
          {
              /* Server side save a copy of SNO just for verify */
              lsquic_str_setto(&hs_ctx->sno, val, len);
          }
          ESHIST_APPEND(enc_session, ESHE_SET_SNO);
          break;
  
      case QTAG_STK:
          if (is_client)
          {
              lsquic_str_setto(&enc_session->info->sstk, val, len);
          }
          else
          {
              /* Server need to save a copy to verify */
              lsquic_str_setto(&hs_ctx->stk, val, len);
          }
          ESHIST_APPEND(enc_session, ESHE_SET_STK);
          break;
  
      case QTAG_SCID:
          if (len != SCID_LENGTH)
              return -1;
          if (is_client)
          {
              memcpy(enc_session->info->sscid, val, len);
          }
          else
          {
              memcpy(hs_ctx->scid, val, len);
              hs_ctx->set |= HSET_SCID;
          }
          ESHIST_APPEND(enc_session, ESHE_SET_SCID);
          break;
  
      case QTAG_AEAD:
          if (is_client)
              enc_session->info->aead = get_tag_value_i32(val, len);
          else
              hs_ctx->aead = get_tag_value_i32(val, len);
          break;
  
      case QTAG_KEXS:
          if (is_client)
          {
              if (head_tag == QTAG_SCFG && 0 == len % 4)
              {
                  const unsigned char *p, *end;
                  unsigned pub_idx, idx;
  #ifdef WIN32
                  pub_idx = 0;
  #endif
  
                  for (p = val; p < val + len; p += 4)
                      if (0 == memcmp(p, "C255", 4))
                      {
                          memcpy(&enc_session->info->kexs, p, 4);
                          pub_idx = (p - val) / 4;
                          LSQ_DEBUG("Parsing SCFG: supported KEXS C255 at "
                                                          "index %u", pub_idx);
                          break;
                      }
                  if (p >= val + len)
                  {
                      LSQ_INFO("supported KEXS not found, trouble ahead");
                      break;
                  }
                  if (lsquic_str_len(&hs_ctx->scfg_pubs) > 0)
                  {
                      p = (const unsigned char *)
                                          lsquic_str_cstr(&hs_ctx->scfg_pubs);
                      end = p + lsquic_str_len(&hs_ctx->scfg_pubs);
  
                      for (idx = 0; p < end; ++idx)
                      {
                          uint32_t sz = 0;
                          if (p + 3 > end)
                              break;
                          sz |= *p++;
                          sz |= *p++ << 8;
                          sz |= *p++ << 16;
                          if (p + sz > end)
                              break;
                          if (idx == pub_idx)
                          {
                              if (sz == 32)
                              {
                                  memcpy(hs_ctx->pubs, p, 32);
                                  memcpy(enc_session->info->spubs, p, 32);
                              }
                              break;
                          }
                          p += sz;
                      }
                  }
                  else
                      LSQ_INFO("No PUBS from SCFG to parse");
              }
          }
          else
              hs_ctx->kexs = get_tag_value_i32(val, len);
          break;
  
      case QTAG_NONC:
          if (len != sizeof(hs_ctx->nonc))
              return -1;
          memcpy(hs_ctx->nonc, val, len);
          break;
  
      case QTAG_SCFG:
          if (is_client)
          {
              lsquic_str_setto(&enc_session->info->scfg, val, len);
              enc_session->info->scfg_flag = 1;
          }
          else
              LSQ_INFO("unexpected SCFG");
          break;
  
      case QTAG_PROF:
          lsquic_str_setto(&hs_ctx->prof, val, len);
          ESHIST_APPEND(enc_session, ESHE_SET_PROF);
          break;
  
      case QTAG_STTL:
          hs_ctx->sttl = get_tag_value_i64(val, len);
          break;
  
      case QTAG_SRST:
          if (enc_session->es_flags & ES_SERVER)
              break;
          if (len != sizeof(hs_ctx->srst))
          {
              LSQ_INFO("Unexpected size of SRST: %u instead of %zu bytes",
                  len, sizeof(hs_ctx->srst));
              return -1;
          }
          memcpy(hs_ctx->srst, val, len);
          hs_ctx->set |= HSET_SRST;
          ESHIST_APPEND(enc_session, ESHE_SET_SRST);
          break;
  
      default:
          LSQ_DEBUG("Ignored tag '%.*s'", 4, (char *)&tag);
          break;
      }
  
      return 0;
  }
  
  
  /* only for the hs stream-frame data, NOT with the packet header or frame header*/
  static enum handshake_error parse_hs (struct lsquic_enc_session *enc_session,
                                        const unsigned char *buf, int buf_len,
                                        uint32_t *head_tag)
  {
      uint16_t i;
      const unsigned char *p = buf;
      const unsigned char *pend = buf + buf_len;
  
      unsigned char *data;
      uint32_t len = 0, offset = 0;
      uint16_t num;
      uint32_t tag;
      if (buf_len < 6)
          return DATA_FORMAT_ERROR;
  
      memcpy(&tag, p, 4);
      p += 4;
  
      if (enc_session->es_flags & ES_SERVER)
      {   /* Server only expects to receive CHLO messages from the client */
          if (tag != QTAG_CHLO)
              return DATA_FORMAT_ERROR;
      }
      else
      {
          if (tag != QTAG_SREJ && tag != QTAG_REJ && tag != QTAG_SHLO &&
                                                          tag != QTAG_SCFG)
              return DATA_FORMAT_ERROR;
      }
  
      *head_tag = tag;
  
      memcpy((char *)&num, p, 2);
      p += 2 + 2;  /* the 2 bytes padding 0x0000 need to be bypassed */
  
      if (num < 1)
          return DATA_FORMAT_ERROR;
  
      data = (uint8_t *)(buf + 4 * 2 * (1 + num));
      if ((const char *)data > (const char *)pend)
      {
          LSQ_DEBUG("parse_hs tag '%.*s' error: data not enough", 4, (char *)head_tag);
          return DATA_NOT_ENOUGH;
      }
  
      /* check last offset */
      memcpy((char *)&len, data - 4, 4);
      if ((const char *)data + len > (const char *)pend)
      {
          LSQ_DEBUG("parse_hs tag '%.*s' error: data not enough!!!", 4, (char *)head_tag);
          return DATA_NOT_ENOUGH;
      }
  
      for (i=0; i<num; ++i)
      {
          memcpy((char *)&tag, p, 4);
          p += 4;
          memcpy((char *)&len, p, 4);
          len -= offset;
          p += 4;
  
          if ((const char *)data + offset + len > (const char *)pend)
              return DATA_FORMAT_ERROR;
  
          if (0 != parse_hs_data(enc_session, tag, data + offset, len,
                                                                  *head_tag))
              return DATA_FORMAT_ERROR;
          offset += len;
      }
  
      LSQ_DEBUG("parse_hs tag '%.*s' no error.", 4, (char *)head_tag);
      return DATA_NO_ERROR;
  }
  
  
  static uint32_t get_tag_value_i32(unsigned char *val, int len)
  {
      uint32_t v;
      if (len < 4)
          return 0;
      memcpy(&v, val, 4);
      return v;
  }
  
  
  static uint64_t get_tag_value_i64(unsigned char *val, int len)
  {
      uint64_t v;
      if (len < 8)
          return 0;
      memcpy(&v, val, 8);
      return v;
  }
  
  
  static int
  get_tag_val_u32 (unsigned char *v, int len, uint32_t *val)
  {
      if (len != 4)
          return -1;
      memcpy(val, v, 4);
      return 0;
  }
  
  
  /*  From "QUIC Crypto" for easy reference:
   *
   *  A handshake message consists of:
   *    - The tag of the message.
   *    - A uint16 containing the number of tag-value pairs.
   *    - Two bytes of padding which should be zero when sent but ignored when
   *          received.
   *    - A series of uint32 tags and uint32 end offsets, one for each
   *          tag-value pair. The tags must be strictly monotonically
   *          increasing, and the end-offsets must be monotonic non-decreasing.
   *          The end offset gives the offset, from the start of the value
   *          data, to a byte one beyond the end of the data for that tag.
   *          (Thus the end offset of the last tag contains the length of the
   *          value data).
   *    - The value data, concatenated without padding.
   */
  
  struct table_entry { uint32_t tag, off; };
  
  struct message_writer
  {
      unsigned char       *mw_p;
      struct table_entry   mw_first_dummy_entry;
      struct table_entry  *mw_entry,
                          *mw_prev_entry,
                          *mw_end;
  };
  
  /* MW_ family of macros is used to write entries to handshake message
   * (MW stands for "message writer").
   */
  #define MW_BEGIN(mw, msg_tag, n_entries, data_ptr) do {             \
      uint32_t t_ = msg_tag;                                          \
      uint16_t n_ = n_entries;                                        \
      memcpy(data_ptr, &t_, 4);                                       \
      memcpy(data_ptr + 4, &n_, 2);                                   \
      memset(data_ptr + 4 + 2, 0, 2);                                 \
      (mw)->mw_entry = (void *) (data_ptr + 8);                       \
      (mw)->mw_p = data_ptr + 8 +                                     \
                      (n_entries) * sizeof((mw)->mw_entry[0]);        \
      (mw)->mw_first_dummy_entry.tag = 0;                             \
      (mw)->mw_first_dummy_entry.off = 0;                             \
      (mw)->mw_prev_entry = &(mw)->mw_first_dummy_entry;              \
      (mw)->mw_end = (void *) (mw)->mw_p;                             \
  } while (0)
  
  #ifndef NDEBUG
  #   define MW_END(mw) do {                                          \
          assert((mw)->mw_entry == (mw)->mw_end);                     \
      } while (0)
  #else
  #   define MW_END(mw)
  #endif
  
  #define MW_P(mw) ((mw)->mw_p)
  
  #define MW_ADVANCE_P(mw, n) do {                                    \
      MW_P(mw) += (n);                                                \
  } while (0)
  
  #define MW_WRITE_TABLE_ENTRY(mw, tag_, sz) do {                     \
      assert((mw)->mw_prev_entry->tag < (tag_));                      \
      assert((mw)->mw_entry < (mw)->mw_end);                          \
      (mw)->mw_entry->tag = (tag_);                                   \
      (mw)->mw_entry->off = (mw)->mw_prev_entry->off + (sz);          \
      (mw)->mw_prev_entry = (mw)->mw_entry;                           \
      ++(mw)->mw_entry;                                               \
  } while (0)
  
  #define MW_WRITE_BUFFER(mw, tag, buf, sz) do {                      \
      MW_WRITE_TABLE_ENTRY(mw, tag, sz);                              \
      memcpy(MW_P(mw), buf, sz);                                      \
      MW_ADVANCE_P(mw, sz);                                           \
  } while (0)
  
  #define MW_WRITE_LS_STR(mw, tag, s) \
      MW_WRITE_BUFFER(mw, tag, lsquic_str_buf(s), lsquic_str_len(s))
  
  #define MW_WRITE_UINT32(mw, tag, val) do {                          \
      uint32_t v_ = (val);                                            \
      MW_WRITE_BUFFER(mw, tag, &v_, sizeof(v_));                      \
  } while (0)
  
  #define MW_WRITE_UINT64(mw, tag, val) do {                          \
      uint64_t v_ = (val);                                            \
      MW_WRITE_BUFFER(mw, tag, &v_, sizeof(v_));                      \
  } while (0)
  
  
  /* MSG_LEN_ family of macros calculates buffer size required for a
   * handshake message.
   */
  #define MSG_LEN_INIT(len) do {                                      \
      len = 4 /* Tag */ + 2 /* # tags */ + 2 /* Two zero bytes */;    \
  } while (0)
  
  #define MSG_LEN_ADD(len, payload_sz) do {                           \
      len += 4 + 4 + (payload_sz);                                    \
  } while (0)
  
  #define MSG_LEN_VAL(len) (+(len))
  
  
  static int
  lsquic_enc_session_gen_chlo (enc_session_t *enc_session_p,
                          enum lsquic_version version, uint8_t *buf, size_t *len)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      int include_pad;
      const lsquic_str_t *const ccs = lsquic_get_common_certs_hash();
      const struct lsquic_engine_settings *const settings =
                                          &enc_session->enpub->enp_settings;
      c_cert_item_t *const cert_item = enc_session->cert_item;
      unsigned char pub_key[32];
      size_t ua_len;
      uint32_t opts[1];  /* Only NSTP is supported for now */
      unsigned n_opts, msg_len, n_tags, pad_size;
      struct message_writer mw;
  
      /* Before we do anything else, sanity check: */
      if (*len < MIN_CHLO_SIZE)
          return -1;
  
      n_opts = 0;
      /* CHLO is not regenerated during version negotiation.  Hence we always
       * include this option to cover the case when Q044 or Q046 gets negotiated
       * down.
       */
      if (settings->es_support_nstp)
          opts[ n_opts++ ] = QTAG_NSTP;
  
      /* Count tags and calculate required buffer size: */
      MSG_LEN_INIT(msg_len);                  n_tags = 0;
      MSG_LEN_ADD(msg_len, 4);                ++n_tags;           /* PDMD */
      MSG_LEN_ADD(msg_len, 4);                ++n_tags;           /* AEAD */
      MSG_LEN_ADD(msg_len, 4);                ++n_tags;           /* VER  */
      MSG_LEN_ADD(msg_len, 4);                ++n_tags;           /* MIDS */
      MSG_LEN_ADD(msg_len, 4);                ++n_tags;           /* SCLS */
      MSG_LEN_ADD(msg_len, 4);                ++n_tags;           /* CFCW */
      MSG_LEN_ADD(msg_len, 4);                ++n_tags;           /* SFCW */
      MSG_LEN_ADD(msg_len, 4);                ++n_tags;           /* ICSL */
      MSG_LEN_ADD(msg_len, 4);                ++n_tags;           /* SMHL */
      MSG_LEN_ADD(msg_len, 4);                ++n_tags;           /* KEXS */
      MSG_LEN_ADD(msg_len, 0);                ++n_tags;           /* CSCT */
      if (n_opts > 0)
      {
          MSG_LEN_ADD(msg_len, sizeof(opts[0]) * n_opts);
                                              ++n_tags;           /* COPT */
      }
      if (settings->es_ua)
      {
          ua_len = strlen(settings->es_ua);
          if (ua_len > 0)
          {
              MSG_LEN_ADD(msg_len, ua_len);   ++n_tags;           /* UAID */
          }
      }
      else
          ua_len = 0;
      if (settings->es_support_tcid0)
      {
          MSG_LEN_ADD(msg_len, 4);            ++n_tags;           /* TCID */
      }
      MSG_LEN_ADD(msg_len, lsquic_str_len(&enc_session->hs_ctx.sni));
                                              ++n_tags;           /* SNI  */
      MSG_LEN_ADD(msg_len, lsquic_str_len(ccs));  ++n_tags;           /* CCS  */
      if (cert_item)
      {
          enc_session->cert_ptr = &cert_item->crts[0];
          MSG_LEN_ADD(msg_len, lsquic_str_len(cert_item->hashs));
                                              ++n_tags;           /* CCRT */
          MSG_LEN_ADD(msg_len, 8);            ++n_tags;           /* XLCT */
      }
      MSG_LEN_ADD(msg_len, lsquic_str_len(&enc_session->ssno));
                                              ++n_tags;           /* SNO  */
      MSG_LEN_ADD(msg_len, lsquic_str_len(&enc_session->info->sstk));
                                              ++n_tags;           /* STK  */
      if (lsquic_str_len(&enc_session->info->scfg) > 0)
      {
          MSG_LEN_ADD(msg_len, sizeof(enc_session->info->sscid));
                                              ++n_tags;           /* SCID */
          if (enc_session->cert_ptr)
          {
              MSG_LEN_ADD(msg_len, sizeof(pub_key));
                                              ++n_tags;           /* PUBS */
              MSG_LEN_ADD(msg_len, sizeof(enc_session->hs_ctx.nonc));
                                              ++n_tags;           /* NONC */
              RAND_bytes(enc_session->priv_key, 32);
              lsquic_c255_get_pub_key(enc_session->priv_key, pub_key);
              lsquic_gen_nonce_c(enc_session->hs_ctx.nonc, enc_session->info->orbt);
          }
      }
      include_pad = MSG_LEN_VAL(msg_len) < MIN_CHLO_SIZE;
      if (include_pad)
      {
          if (MSG_LEN_VAL(msg_len) + sizeof(struct table_entry) < MIN_CHLO_SIZE)
              pad_size = MIN_CHLO_SIZE - MSG_LEN_VAL(msg_len) -
                                                  sizeof(struct table_entry);
          else
              pad_size = 0;
          MSG_LEN_ADD(msg_len, pad_size);     ++n_tags;           /* PAD  */
      }
  #ifdef WIN32
      else
          pad_size = 0;
  #endif
  
      /* Check that we have enough room in the output buffer: */
      if (MSG_LEN_VAL(msg_len) > *len)
          return -1;
  
      /* Write CHLO: */
      MW_BEGIN(&mw, QTAG_CHLO, n_tags, buf);
      if (include_pad)
      {
          memset(MW_P(&mw), '-', pad_size);
          MW_WRITE_TABLE_ENTRY(&mw, QTAG_PAD, pad_size);
          MW_ADVANCE_P(&mw, pad_size);
      }
      MW_WRITE_LS_STR(&mw, QTAG_SNI, &enc_session->hs_ctx.sni);
      MW_WRITE_LS_STR(&mw, QTAG_STK, &enc_session->info->sstk);
      MW_WRITE_LS_STR(&mw, QTAG_SNO, &enc_session->ssno);
      MW_WRITE_UINT32(&mw, QTAG_VER, lsquic_ver2tag(version));
      MW_WRITE_LS_STR(&mw, QTAG_CCS, ccs);
      if (lsquic_str_len(&enc_session->info->scfg) > 0 && enc_session->cert_ptr)
          MW_WRITE_BUFFER(&mw, QTAG_NONC, enc_session->hs_ctx.nonc,
                                          sizeof(enc_session->hs_ctx.nonc));
      MW_WRITE_UINT32(&mw, QTAG_AEAD, settings->es_aead);
      if (ua_len)
          MW_WRITE_BUFFER(&mw, QTAG_UAID, settings->es_ua, ua_len);
      if (lsquic_str_len(&enc_session->info->scfg) > 0)
          MW_WRITE_BUFFER(&mw, QTAG_SCID, enc_session->info->sscid,
                                          sizeof(enc_session->info->sscid));
      if (settings->es_support_tcid0)
          MW_WRITE_UINT32(&mw, QTAG_TCID, 0);
      MW_WRITE_UINT32(&mw, QTAG_PDMD, settings->es_pdmd);
      MW_WRITE_UINT32(&mw, QTAG_SMHL, 1);
      MW_WRITE_UINT32(&mw, QTAG_ICSL, settings->es_idle_conn_to / 1000000);
      if (lsquic_str_len(&enc_session->info->scfg) > 0 && enc_session->cert_ptr)
          MW_WRITE_BUFFER(&mw, QTAG_PUBS, pub_key, sizeof(pub_key));
      MW_WRITE_UINT32(&mw, QTAG_MIDS, settings->es_max_streams_in);
      MW_WRITE_UINT32(&mw, QTAG_SCLS, settings->es_silent_close);
      MW_WRITE_UINT32(&mw, QTAG_KEXS, settings->es_kexs);
      if (cert_item)
          MW_WRITE_BUFFER(&mw, QTAG_XLCT, lsquic_str_buf(cert_item->hashs), 8);
      /* CSCT is empty on purpose (retained from original code) */
      MW_WRITE_TABLE_ENTRY(&mw, QTAG_CSCT, 0);
      if (n_opts > 0)
          MW_WRITE_BUFFER(&mw, QTAG_COPT, opts, n_opts * sizeof(opts[0]));
      if (cert_item)
          MW_WRITE_LS_STR(&mw, QTAG_CCRT, cert_item->hashs);
      MW_WRITE_UINT32(&mw, QTAG_CFCW, settings->es_cfcw);
      MW_WRITE_UINT32(&mw, QTAG_SFCW, settings->es_sfcw);
      MW_END(&mw);
      assert(buf + *len >= MW_P(&mw));
  
      *len = MW_P(&mw) - buf;
  
      lsquic_str_setto(&enc_session->chlo, buf, *len);
  
      if (lsquic_str_len(&enc_session->info->scfg) > 0 && enc_session->cert_ptr)
      {
          enc_session->have_key = 0;
          assert(lsquic_str_len(enc_session->cert_ptr) > 0);
          determine_keys(enc_session);
          enc_session->have_key = 1;
      }
  
      LSQ_DEBUG("lsquic_enc_session_gen_chlo called, return 0, buf_len %zd.", *len);
      return 0;
  }
  
  
  static enum handshake_error
  determine_rtts (struct lsquic_enc_session *enc_session,
                                      const struct sockaddr *ip_addr, time_t t)
  {
      hs_ctx_t *const hs_ctx = &enc_session->hs_ctx;
      enum hsk_failure_reason hfr;
  
      if (!(hs_ctx->set & HSET_SCID))
      {
          hs_ctx->rrej = HFR_CONFIG_INCHOATE_HELLO;
          ESHIST_APPEND(enc_session, ESHE_MISSING_SCID);
          goto fail_1rtt;
      }
  
      hfr = lsquic_verify_stk(enc_session, ip_addr, t, &hs_ctx->stk);
      if (hfr != HFR_HANDSHAKE_OK)
      {
          hs_ctx->rrej = hfr;
          ESHIST_APPEND(enc_session, ESHE_VSTK_FAILED);
          goto fail_1rtt;
      }
      else
          ESHIST_APPEND(enc_session, ESHE_VSTK_OK);
  
      if (memcmp(enc_session->server_config->lsc_scfg->info.sscid, hs_ctx->scid, 16) != 0)
      {
          hs_ctx->rrej = HFR_CONFIG_UNKNOWN_CONFIG;
          ESHIST_APPEND(enc_session, ESHE_UNKNOWN_CONFIG);
          goto fail_1rtt;
      }
  
      if (!(lsquic_str_len(&hs_ctx->ccrt) > 0))
      {
          /* We provide incorrect RREJ here because there is not one that fits
           * this case.  We can tell them apart: one comes in SREJ, the other
           * in REJ.
           */
          hs_ctx->rrej = HFR_CONFIG_INCHOATE_HELLO;
          ESHIST_APPEND(enc_session, ESHE_EMPTY_CCRT);
          goto fail_1rtt;
      }
  
      if (lsquic_str_len(&enc_session->ssno) > 0)
      {
          if (lsquic_str_len(&hs_ctx->sno) == 0)
          {
              hs_ctx->rrej = HFR_SERVER_NONCE_REQUIRED;
              ESHIST_APPEND(enc_session, ESHE_MISSING_SNO);
              goto fail_1rtt;
          }
          else if (lsquic_str_bcmp(&enc_session->ssno, &hs_ctx->sno) != 0)
          {
              hs_ctx->rrej = HFR_SERVER_NONCE_INVALID;
              ESHIST_APPEND(enc_session, ESHE_SNO_MISMATCH);
              goto fail_1rtt;
          }
          else
              ESHIST_APPEND(enc_session, ESHE_SNO_OK);
      }
  
      enc_session->hsk_state = HSK_SHLO;
      memcpy(enc_session->priv_key, enc_session->server_config->lsc_scfg->info.priv_key, 32);
      return HS_SHLO;
  
    fail_1rtt:
      enc_session->hsk_state = HSK_CHLO_REJ;
      return HS_1RTT;
  }
  
  
  static int
  config_has_correct_size (const struct lsquic_enc_session *enc_session,
                                              const void *data, unsigned shm_len)
  {
      /* EVP_AEAD_CTX from boringssl after-18d9f28f0df9f95570. */
      struct new_evp_aead_ctx_st {
          void *ptr1;     /* aead */
          void *ptr2;     /* aead_state */
          uint8_t tag_len;
      };
  
      /* This is how SHM would like in 5.2.1 builds 7 and 8: */
      struct old_scfg_info
      {
          unsigned char   sscid[SCID_LENGTH];
          unsigned char   priv_key[32];
          unsigned char   skt_key[16];
          uint32_t        aead;
          uint32_t        kexs;
          uint32_t        pdmd;
          uint64_t        orbt;
          uint64_t        expy;
          struct new_evp_aead_ctx_st ctx;
          short           scfg_len;
      };
  
      const SCFG_t               *const modern_config = data;
      const struct old_scfg_info *const old_info      = data;
      size_t expected_size;
  
      expected_size = modern_config->info.scfg_len + sizeof(*modern_config);
      if (expected_size == shm_len)
          return 1;
  
      if (old_info->scfg_len + sizeof(*old_info) == shm_len)
      {
          LSQ_WARN("Generating new server config");
          return 0;
      }
  
      LSQ_ERROR("Server config has size %u -- expected %zd", shm_len,
                                                              expected_size);
      return 0;
  }
  
  
  static lsquic_server_config_t *
  get_valid_scfg (const struct lsquic_enc_session *enc_session,
                                      const struct lsquic_engine_public *enpub)
  {
  #define SERVER_SCFG_KEY         "SERVER_SCFG"
  #define SERVER_SCFG_KEY_SIZE    (sizeof(SERVER_SCFG_KEY) - 1)
      const struct lsquic_engine_settings *const settings = &enpub->enp_settings;
      const struct lsquic_shared_hash_if *const shi = enpub->enp_shi;
      void *const shi_ctx = enpub->enp_shi_ctx;
      uint8_t spubs[35] = {0x20, 0, 0, };/* need to init first 3 bytes */
      time_t t = time(NULL);
      unsigned int real_len;
      SCFG_info_t *temp_scfg;
      SCFG_t *tmp_scfg_copy = NULL;
      void *scfg_ptr;
      int ret;
      unsigned msg_len, server_config_sz;
      struct message_writer mw;
  
      if (enc_session->enpub->enp_server_config->lsc_scfg && (enc_session->enpub->enp_server_config->lsc_scfg->info.expy > (uint64_t)t))
          return enc_session->enpub->enp_server_config;
  
      ret = shi->shi_lookup(shi_ctx, SERVER_SCFG_KEY, SERVER_SCFG_KEY_SIZE,
                            &scfg_ptr, &real_len);
      if (ret == 1)
      {
          if (config_has_correct_size(enc_session, scfg_ptr, real_len) &&
                  (enc_session->enpub->enp_server_config->lsc_scfg = scfg_ptr,
                              enc_session->enpub->enp_server_config->lsc_scfg->info.expy > (uint64_t)t))
          {
              /* Why need to init here, because this memory may be read from SHM,
               * the struct is ready but AEAD_CTX is not ready.
               **/
              EVP_AEAD_CTX_init(&enc_session->enpub->enp_server_config->lsc_stk_ctx, EVP_aead_aes_128_gcm(),
                                enc_session->enpub->enp_server_config->lsc_scfg->info.skt_key, 16, 12, NULL);
              return enc_session->enpub->enp_server_config;
          }
          else
          {
              shi->shi_delete(shi_ctx, SERVER_SCFG_KEY, SERVER_SCFG_KEY_SIZE);
          }
      }
  
      MSG_LEN_INIT(msg_len);
      MSG_LEN_ADD(msg_len, sizeof(temp_scfg->sscid));
      MSG_LEN_ADD(msg_len, sizeof(spubs));
      MSG_LEN_ADD(msg_len, enpub->enp_ver_tags_len);
      MSG_LEN_ADD(msg_len, sizeof(temp_scfg->aead));
      MSG_LEN_ADD(msg_len, sizeof(temp_scfg->kexs));
      MSG_LEN_ADD(msg_len, sizeof(temp_scfg->pdmd));
      MSG_LEN_ADD(msg_len, sizeof(temp_scfg->orbt));
      MSG_LEN_ADD(msg_len, sizeof(temp_scfg->expy));
  
      server_config_sz = sizeof(*enc_session->enpub->enp_server_config->lsc_scfg) + MSG_LEN_VAL(msg_len);
      enc_session->enpub->enp_server_config->lsc_scfg = malloc(server_config_sz);
      if (!enc_session->enpub->enp_server_config->lsc_scfg)
          return NULL;
  
      temp_scfg = &enc_session->enpub->enp_server_config->lsc_scfg->info;
      RAND_bytes(temp_scfg->skt_key, sizeof(temp_scfg->skt_key));
      RAND_bytes(temp_scfg->sscid, sizeof(temp_scfg->sscid));
      RAND_bytes(temp_scfg->priv_key, sizeof(temp_scfg->priv_key));
      lsquic_c255_get_pub_key(temp_scfg->priv_key, spubs + 3);
      temp_scfg->aead = settings->es_aead;
      temp_scfg->kexs = settings->es_kexs;
      temp_scfg->pdmd = settings->es_pdmd;
      temp_scfg->orbt = 0;
      temp_scfg->expy = t + settings->es_sttl;
  
      MW_BEGIN(&mw, QTAG_SCFG, 8, enc_session->enpub->enp_server_config->lsc_scfg->scfg);
      MW_WRITE_BUFFER(&mw, QTAG_VER, enpub->enp_ver_tags_buf,
                                                  enpub->enp_ver_tags_len);
      MW_WRITE_UINT32(&mw, QTAG_AEAD, temp_scfg->aead);
      MW_WRITE_BUFFER(&mw, QTAG_SCID, temp_scfg->sscid, sizeof(temp_scfg->sscid));
      MW_WRITE_UINT32(&mw, QTAG_PDMD, temp_scfg->pdmd);
      MW_WRITE_BUFFER(&mw, QTAG_PUBS, spubs, sizeof(spubs));
      MW_WRITE_UINT32(&mw, QTAG_KEXS, temp_scfg->kexs);
      MW_WRITE_UINT64(&mw, QTAG_ORBT, temp_scfg->orbt);
      MW_WRITE_UINT64(&mw, QTAG_EXPY, temp_scfg->expy);
      MW_END(&mw);
      assert(MW_P(&mw) == enc_session->enpub->enp_server_config->lsc_scfg->scfg + MSG_LEN_VAL(msg_len));
  
      temp_scfg->scfg_len = MSG_LEN_VAL(msg_len);
  
      LSQ_DEBUG("%s called, return len %d.", __func__, temp_scfg->scfg_len);
  
  //     /* TODO: will shi_delete call free to release the buffer? */
  //     shi->shi_delete(shi_ctx, SERVER_SCFG_KEY, SERVER_SCFG_KEY_SIZE);
      void *scfg_key = strdup(SERVER_SCFG_KEY);
      shi->shi_insert(shi_ctx, scfg_key, SERVER_SCFG_KEY_SIZE,
              enc_session->enpub->enp_server_config->lsc_scfg, server_config_sz, t + settings->es_sttl);
  
      ret = shi->shi_lookup(shi_ctx, scfg_key, SERVER_SCFG_KEY_SIZE,
                            &scfg_ptr, &real_len);
      if (ret == 1)
      {
          tmp_scfg_copy = scfg_ptr;
          if (tmp_scfg_copy != enc_session->enpub->enp_server_config->lsc_scfg)
          {
              free(enc_session->enpub->enp_server_config->lsc_scfg);
              enc_session->enpub->enp_server_config->lsc_scfg = tmp_scfg_copy;
          }
      }
      else
      {
          /* Since internal error occured, but I have to use a SCFG, log it*/
          LSQ_DEBUG("get_valid_scfg got an shi internal error.\n");
      }
  
      ret = EVP_AEAD_CTX_init(&enc_session->enpub->enp_server_config->lsc_stk_ctx, EVP_aead_aes_128_gcm(),
                                enc_session->enpub->enp_server_config->lsc_scfg->info.skt_key,
                                sizeof(enc_session->enpub->enp_server_config->lsc_scfg->info.skt_key), 12, NULL);
  
      LSQ_DEBUG("get_valid_scfg::EVP_AEAD_CTX_init return %d.", ret);
      return enc_session->enpub->enp_server_config;
  }
  
  
  static int
  generate_crt (struct lsquic_enc_session *enc_session, int common_case)
  {
      int i, n, len, crt_num, rv = -1;
      lsquic_str_t **crts;
      unsigned char *out;
      X509* crt;
      STACK_OF(X509)      *pXchain;
      SSL_CTX *const ctx = enc_session->ssl_ctx;
      hs_ctx_t *const hs_ctx = &enc_session->hs_ctx;
      struct compressed_cert *ccert;
  
      SSL_CTX_get0_chain_certs(ctx, &pXchain);
      n = sk_X509_num(pXchain);
      crt_num = n + 1;
  
      crts = calloc(crt_num, sizeof(crts[0]));
      if (!crts)
          return -1;
  
      crts[0] = lsquic_str_new(lsquic_str_cstr(enc_session->cert_ptr),
                                      lsquic_str_len(enc_session->cert_ptr));
      if (!crts[0])
          goto cleanup;
  
      for (i = 1; i < crt_num; i++)
      {
          crt = sk_X509_value(pXchain, i - 1);
          out = NULL;
          len = i2d_X509(crt, &out);
          if (len < 0)
              goto cleanup;
          crts[i] = lsquic_str_new((const char *) out, len);
          OPENSSL_free(out);
      }
  
      ccert = lsquic_compress_certs(crts, crt_num, &hs_ctx->ccs, &hs_ctx->ccrt);
      if (!ccert)
          goto cleanup;
  
      if (common_case)
      {
          if (SSL_CTX_set_ex_data(ctx, s_ccrt_idx, ccert))
              ++ccert->refcnt;
          else
          {
              free(ccert);
              ccert = NULL;
              goto cleanup;
          }
      }
  
      ++ccert->refcnt;
      hs_ctx->ccert = ccert;
  
      /* We got here, set rv to 0: success */
      rv = 0;
  
    cleanup:
      for (i = 0; i < crt_num; ++i)
          if (crts[i])
              lsquic_str_delete(crts[i]);
      free(crts);
      return rv;
  }
  
  
  /* rtt == 1 case */
  static int
  gen_rej1_data (struct lsquic_enc_session *enc_session, uint8_t *data,
                      size_t max_len, const struct sockaddr *ip, time_t t)
  {
  #ifndef WIN32
  #   define ERR(e_) do { return (e_); } while (0)
  #else
  #   define ERR(e_) do { len = (e_); goto end; } while (0)
  #endif
      int len;
      EVP_PKEY * rsa_priv_key;
      SSL_CTX *ctx = enc_session->ssl_ctx;
      hs_ctx_t *const hs_ctx = &enc_session->hs_ctx;
      int scfg_len = enc_session->server_config->lsc_scfg->info.scfg_len;
      uint8_t *scfg_data = enc_session->server_config->lsc_scfg->scfg;
      int common_case;
      size_t msg_len;
      struct message_writer mw;
      uint64_t sttl;
  
      rsa_priv_key = SSL_CTX_get0_privatekey(ctx);
      if (!rsa_priv_key)
          return -1;
  
      size_t prof_len = (size_t) EVP_PKEY_size(rsa_priv_key);
  #ifndef WIN32
      char prof_buf[prof_len];
  #else
      char *prof_buf = _malloca(prof_len);
      if (!prof_buf)
          return -1;
  #endif
  
      if (hs_ctx->ccert)
      {
          put_compressed_cert(hs_ctx->ccert);
          hs_ctx->ccert = NULL;
      }
  
      /**
       * Only cache hs_ctx->ccs is the hardcoded common certs and hs_ctx->ccrt is empty case
       * This is the most common case
       */
      common_case = lsquic_str_len(&hs_ctx->ccrt) == 0
                 && lsquic_str_bcmp(&hs_ctx->ccs, lsquic_get_common_certs_hash()) == 0;
      if (common_case)
          hs_ctx->ccert = SSL_CTX_get_ex_data(ctx, s_ccrt_idx);
  
      if (hs_ctx->ccert)
      {
          ++hs_ctx->ccert->refcnt;
          LSQ_DEBUG("use cached compressed cert");
      }
      else if (0 == generate_crt(enc_session, common_case))
          LSQ_DEBUG("generated compressed cert");
      else
      {
          LSQ_INFO("cannot could not generate compressed cert for");
          ERR(-1);
      }
  
      LSQ_DEBUG("gQUIC rej1 data");
      LSQ_DEBUG("gQUIC NOT enabled");
      const int s = lsquic_gen_prof((const uint8_t *)lsquic_str_cstr(&enc_session->chlo),
           (size_t)lsquic_str_len(&enc_session->chlo),
           scfg_data, scfg_len,
           rsa_priv_key, (uint8_t *)prof_buf, &prof_len);
      if (s != 0)
      {
          LSQ_INFO("could not generate server proof, code %d", s);
          ERR(-1);
      }
  
      lsquic_str_setto(&hs_ctx->prof, prof_buf, prof_len);
  
      if (!hs_ctx->rrej)
      {
          LSQ_WARN("REJ: RREJ is not set, use default");
          hs_ctx->rrej = HFR_CLIENT_NONCE_UNKNOWN;
      }
  
      MSG_LEN_INIT(msg_len);
      MSG_LEN_ADD(msg_len, sizeof(hs_ctx->rrej));
      MSG_LEN_ADD(msg_len, scfg_len);
      MSG_LEN_ADD(msg_len, STK_LENGTH);
      MSG_LEN_ADD(msg_len, SNO_LENGTH);
      MSG_LEN_ADD(msg_len, sizeof(sttl));
      MSG_LEN_ADD(msg_len, lsquic_str_len(&hs_ctx->prof));
      if (hs_ctx->ccert)
          MSG_LEN_ADD(msg_len, hs_ctx->ccert->len);
  
      if (MSG_LEN_VAL(msg_len) > max_len)
          ERR(-1);
  
      memcpy(enc_session->priv_key, enc_session->server_config->lsc_scfg->info.priv_key, 32);
  
      if (lsquic_str_len(&enc_session->sstk) != STK_LENGTH)
      {
          lsquic_str_d(&enc_session->sstk);
          lsquic_str_prealloc(&enc_session->sstk, STK_LENGTH);
          lsquic_str_setlen(&enc_session->sstk, STK_LENGTH);
      }
      lsquic_gen_stk(enc_session->server_config, ip, t,
                          (unsigned char *) lsquic_str_buf(&enc_session->sstk));
  
      if (lsquic_str_len(&enc_session->ssno) != SNO_LENGTH)
      {
          lsquic_str_d(&enc_session->ssno);
          lsquic_str_prealloc(&enc_session->ssno, SNO_LENGTH);
          lsquic_str_setlen(&enc_session->ssno, SNO_LENGTH);
      }
      RAND_bytes((uint8_t *) lsquic_str_buf(&enc_session->ssno), SNO_LENGTH);
      sttl = enc_session->enpub->enp_server_config->lsc_scfg->info.expy
                                                      - (uint64_t) time(NULL);
  
      MW_BEGIN(&mw, QTAG_REJ, 7, data);
      MW_WRITE_LS_STR(&mw, QTAG_STK, &enc_session->sstk);
      MW_WRITE_LS_STR(&mw, QTAG_SNO, &enc_session->ssno);
      MW_WRITE_LS_STR(&mw, QTAG_PROF, &hs_ctx->prof);
      MW_WRITE_BUFFER(&mw, QTAG_SCFG, scfg_data, scfg_len);
      MW_WRITE_BUFFER(&mw, QTAG_RREJ, &hs_ctx->rrej, sizeof(hs_ctx->rrej));
      MW_WRITE_BUFFER(&mw, QTAG_STTL, &sttl, sizeof(sttl));
      if (hs_ctx->ccert)
          MW_WRITE_BUFFER(&mw, QTAG_CRT, hs_ctx->ccert->buf, hs_ctx->ccert->len);
      MW_END(&mw);
  
      assert(data + max_len >= MW_P(&mw));
      len = MW_P(&mw) - data;
      LSQ_DEBUG("gen_rej1_data called, return len %d.", len);
  #ifdef WIN32
    end:
      _freea(prof_buf);
  #endif
      return len;
  #undef ERR
  }
  
  
  /* rtt == 0 case */
  static int
  gen_shlo_data (uint8_t *buf, size_t buf_len, struct lsquic_enc_session *enc_session,
                    enum lsquic_version version, const struct sockaddr *ip,
                    time_t t, uint8_t *nonce)
  {
      char pub_key[32];
      const struct lsquic_engine_settings *const settings =
                                          &enc_session->enpub->enp_settings;
      struct message_writer mw;
      int len;
      const int include_reset_token = version >= LSQVER_046;
      size_t msg_len;
  
      MSG_LEN_INIT(msg_len);
      MSG_LEN_ADD(msg_len, enc_session->enpub->enp_ver_tags_len);
      MSG_LEN_ADD(msg_len, sizeof(pub_key));
      MSG_LEN_ADD(msg_len, 4);    /* MIDS */
      MSG_LEN_ADD(msg_len, 4);    /* CFCW */
      MSG_LEN_ADD(msg_len, 4);    /* SFCW */
      MSG_LEN_ADD(msg_len, 4);    /* ICSL */
      MSG_LEN_ADD(msg_len, 4);    /* SMHL */
      MSG_LEN_ADD(msg_len, lsquic_str_len(&enc_session->sstk));
      MSG_LEN_ADD(msg_len, lsquic_str_len(&enc_session->ssno));
      if (include_reset_token)
          MSG_LEN_ADD(msg_len, SRST_LENGTH);
  
      if (MSG_LEN_VAL(msg_len) > buf_len)
          return -1;
  
      RAND_bytes(nonce, 32);
      RAND_bytes(enc_session->priv_key, 32);
      lsquic_c255_get_pub_key(enc_session->priv_key, (unsigned char *)pub_key);
      if (lsquic_str_len(&enc_session->sstk) != STK_LENGTH)
      {
          lsquic_str_d(&enc_session->sstk);
          lsquic_str_prealloc(&enc_session->sstk, STK_LENGTH);
          lsquic_str_setlen(&enc_session->sstk, STK_LENGTH);
      }
      lsquic_gen_stk(enc_session->server_config, ip, t,
                          (unsigned char *) lsquic_str_buf(&enc_session->sstk));
      if (lsquic_str_len(&enc_session->ssno) != SNO_LENGTH)
      {
          lsquic_str_d(&enc_session->ssno);
          lsquic_str_prealloc(&enc_session->ssno, SNO_LENGTH);
          lsquic_str_setlen(&enc_session->ssno, SNO_LENGTH);
      }
      RAND_bytes((uint8_t *) lsquic_str_buf(&enc_session->ssno), SNO_LENGTH);
  
      MW_BEGIN(&mw, QTAG_SHLO, 9 + include_reset_token, buf);
      MW_WRITE_LS_STR(&mw, QTAG_STK, &enc_session->sstk);
      MW_WRITE_LS_STR(&mw, QTAG_SNO, &enc_session->ssno);
      MW_WRITE_BUFFER(&mw, QTAG_VER, enc_session->enpub->enp_ver_tags_buf,
                                      enc_session->enpub->enp_ver_tags_len);
      MW_WRITE_UINT32(&mw, QTAG_SMHL, 1);
      MW_WRITE_UINT32(&mw, QTAG_ICSL, settings->es_idle_conn_to / 1000000);
      MW_WRITE_BUFFER(&mw, QTAG_PUBS, pub_key, sizeof(pub_key));
      MW_WRITE_UINT32(&mw, QTAG_MIDS, settings->es_max_streams_in);
      if (include_reset_token)
      {
          MW_WRITE_TABLE_ENTRY(&mw, QTAG_SRST, SRST_LENGTH);
          lsquic_tg_generate_sreset(enc_session->enpub->enp_tokgen,
                                                  &enc_session->cid, MW_P(&mw));
          MW_ADVANCE_P(&mw, SRST_LENGTH);
      }
      MW_WRITE_UINT32(&mw, QTAG_CFCW, settings->es_cfcw);
      MW_WRITE_UINT32(&mw, QTAG_SFCW, settings->es_sfcw);
      MW_END(&mw);
  
      assert(buf + buf_len >= MW_P(&mw));
      len = MW_P(&mw) - buf;
      LSQ_DEBUG("gen_shlo_data called, return len %d.", len);
      return len;
  }
  
  
  /* Generate key based on issuer and serial number.  The key has the following
   * structure:
   *
   *      size_t          length of issuer.  This field is required to prevent
   *                        the chance (however remote) that concatenation of
   *                        the next two fields is ambiguous.
   *      uint8_t[]       DER-encoded issuer
   *      uint8_t[]       Serial number represented as sequence of bytes output
   *                        by BN_bn2bin
   *
   * Return size of the key or zero on error.
   */
  static size_t
  gen_iasn_key (X509 *cert, unsigned char *const out, size_t const sz)
  {
      const unsigned char *name_bytes;
      size_t name_sz;
      X509_NAME *name;
      ASN1_INTEGER *sernum;
      BIGNUM *bn;
      unsigned bn_sz;
  
      name = X509_get_issuer_name(cert);
      if (!name)
          return 0;
      if (!X509_NAME_get0_der(name, &name_bytes, &name_sz))
          return 0;
      sernum = X509_get_serialNumber(cert);
      if (!sernum)
          return 0;
      bn = ASN1_INTEGER_to_BN(sernum, NULL);
      if (!bn)
          return 0;
      bn_sz = BN_num_bytes(bn);
      if (sizeof(size_t) + name_sz + bn_sz > sz)
      {
          BN_free(bn);
          return 0;
      }
  
      memcpy(out, &name_sz, sizeof(name_sz));
      memcpy(out + sizeof(name_sz), name_bytes, name_sz);
      BN_bn2bin(bn, out + sizeof(name_sz) +  name_sz);
      BN_free(bn);
  
      return sizeof(name_sz) + name_sz + bn_sz;
  }
  
  
  static enum {
      GET_SNI_OK,
      GET_SNI_ERR,
  }
  
  
  get_sni_SSL_CTX(struct lsquic_enc_session *enc_session, lsquic_lookup_cert_f cb,
                      void *cb_ctx, const struct sockaddr *local)
  {
      X509 *crt = NULL;
      unsigned char *out;
      int len;
      lsquic_str_t crtstr;
      cert_item_t *item;
      struct ssl_ctx_st *ssl_ctx;
      size_t key_sz;
      unsigned char key[0x400];
      
      if (!enc_session->ssl_ctx)
      {
          if (!cb)
              return GET_SNI_ERR;
          ssl_ctx = cb(cb_ctx, local, lsquic_str_cstr(&enc_session->hs_ctx.sni));
          if (ssl_ctx == NULL)
              return GET_SNI_ERR;
          enc_session->ssl_ctx = ssl_ctx;
      }
  
      if (enc_session->cert_ptr == NULL)
      {
          crt = SSL_CTX_get0_certificate(enc_session->ssl_ctx);
          if (!crt)
              return GET_SNI_ERR;
          key_sz = gen_iasn_key(crt, key, sizeof(key));
          if (key_sz)
          {
              item = find_cert(enc_session->enpub, key, key_sz);
              if (item)
                  LSQ_DEBUG("found cert in cache");
              else
              {
                  out = NULL;
                  len = i2d_X509(crt, &out);
                  if (len < 0)
                      return GET_SNI_ERR;
                  lsquic_str_set(&crtstr, (char *) out, len);
                  item = insert_cert(enc_session->enpub, key, key_sz, &crtstr);
                  if (item)
                  {
                      OPENSSL_free(out);
                      LSQ_DEBUG("inserted cert into cache");
                  }
                  else
                  {
                      LSQ_DEBUG("cert insertion failed, keep own copy");
                      goto copy;
                  }
              }
              enc_session->cert_ptr = item->crt;
          }
          else
          {
              LSQ_INFO("cannot generate cert cache key, make copy");
              out = NULL;
              len = i2d_X509(crt, &out);
              if (len < 0)
                  return GET_SNI_ERR;
    copy:     enc_session->cert_ptr = lsquic_str_new((char *) out, len);
              OPENSSL_free(out);
              if (!enc_session->cert_ptr)
                  return GET_SNI_ERR;
              enc_session->es_flags |= ES_FREE_CERT_PTR;
          }
      }
      return GET_SNI_OK;
  }
  
  
  /***
   * Comments: data and len are the frame(s) parsed data, no packet header.
   * return rtt number:
   *      1 for rej1 and 0 for shlo
   *      DATA_NOT_ENOUGH(-2) for not enough data,
   *      DATA_FORMAT_ERROR(-1) all other errors
   *      HS_DELAYED handshake delayed
   */
  static enum handshake_error
  handle_chlo_frames_data(const uint8_t *data, int len,
                                          struct lsquic_enc_session *enc_session,
                                          lsquic_lookup_cert_f cb, void *cb_ctx,
                                          const struct sockaddr *local,
                                          const struct lsquic_shared_hash_if *shi,
                                          void *shi_ctx, const struct sockaddr *ip, time_t t)
  {
      /* start to parse it */
  //     struct lsquic_enc_session *enc_session = retrive_enc_session(cid);
      uint32_t head_tag;
      enum handshake_error rtt;
      int ret;
  
      LSQ_DEBUG("handle_chlo_frames_data called.");
  
      ret = parse_hs(enc_session, data, len, &head_tag);
      if (ret)
      {
          LSQ_DEBUG("handle_chlo_frames_data parse_hs error,s o quit.");
          return ret;
      }
  
      if (head_tag != QTAG_CHLO)
      {
          LSQ_DEBUG("handle_chlo_frames_data got data format error 1.");
          return DATA_FORMAT_ERROR;
      }
  
  
      rtt = determine_rtts(enc_session, ip, t);
      ESHIST_APPEND(enc_session, ESHE_MULTI2_2BITS + rtt);
      lsquic_str_setto(&enc_session->chlo, (const char *)data, len);
      switch (get_sni_SSL_CTX(enc_session, cb, cb_ctx, local))
      {
      case GET_SNI_ERR:
          ESHIST_APPEND(enc_session, ESHE_SNI_FAIL);
          LSQ_DEBUG("handle_chlo_frames_data got data format error 2.");
          return DATA_FORMAT_ERROR;
      default:
          break;
      }
  
  
      LSQ_DEBUG("handle_chlo_frames_data return %d.", rtt);
      return rtt;
  }
  
  
  static int handle_chlo_reply_verify_prof(struct lsquic_enc_session *enc_session,
                                           lsquic_str_t **out_certs,
                                           size_t *out_certs_count,
                                           lsquic_str_t *cached_certs,
                                           int cached_certs_count)
  {
      const unsigned char *dummy = (unsigned char *) "";
      const unsigned char *const in = enc_session->hs_ctx.ccert
                                      ? enc_session->hs_ctx.ccert->buf : dummy;
      const unsigned char *const in_end = enc_session->hs_ctx.ccert
                                      ? in + enc_session->hs_ctx.ccert->len : 0;
      EVP_PKEY *pub_key;
      int ret;
      size_t i;
      X509 *cert, *server_cert;
      STACK_OF(X509) *chain = NULL;
      ret = lsquic_decompress_certs(in, in_end,cached_certs, cached_certs_count,
                             out_certs, out_certs_count);
      if (ret)
          return ret;
  
      server_cert = lsquic_bio_to_crt((const char *)lsquic_str_cstr(out_certs[0]),
                        lsquic_str_len(out_certs[0]), 0);
      pub_key = X509_get_pubkey(server_cert);
      ret = lsquic_verify_prof((const uint8_t *)lsquic_str_cstr(&enc_session->chlo),
                        (size_t)lsquic_str_len(&enc_session->chlo),
                        &enc_session->info->scfg,
                        pub_key,
                        (const uint8_t *)lsquic_str_cstr(&enc_session->hs_ctx.prof),
                        lsquic_str_len(&enc_session->hs_ctx.prof));
      EVP_PKEY_free(pub_key);
      if (ret != 0)
      {
          LSQ_DEBUG("cannot verify server proof");
          goto cleanup;
      }
  
      if (enc_session->enpub->enp_verify_cert)
      {
          chain = sk_X509_new_null();
          sk_X509_push(chain, server_cert);
          for (i = 1; i < *out_certs_count; ++i)
          {
              cert = lsquic_bio_to_crt((const char *)lsquic_str_cstr(out_certs[i]),
                                      lsquic_str_len(out_certs[i]), 0);
              if (cert)
                  sk_X509_push(chain, cert);
              else
              {
                  LSQ_WARN("cannot push certificate to stack");
                  ret = -1;
                  goto cleanup;
              }
          }
          ret = enc_session->enpub->enp_verify_cert(
                                  enc_session->enpub->enp_verify_ctx, chain);
          LSQ_INFO("server certificate verification %ssuccessful",
                                                      ret == 0 ? "" : "not ");
      }
      EV_LOG_CHECK_CERTS(&enc_session->cid, (const lsquic_str_t **)out_certs, *out_certs_count);
  
    cleanup:
      if (chain)
          sk_X509_free(chain);
      X509_free(server_cert);
      return ret;
  }
  
  
  static void
  setup_aead_ctx (const struct lsquic_enc_session *enc_session,
                  EVP_AEAD_CTX **ctx, unsigned char key[], int key_len,
                  unsigned char *key_copy)
  {
      const EVP_AEAD *aead_ = EVP_aead_aes_128_gcm();
      const int auth_tag_size = enc_session->es_flags & ES_GQUIC2
                                      ? IQUIC_TAG_LEN : GQUIC_PACKET_HASH_SZ;
      if (*ctx)
      {
          EVP_AEAD_CTX_cleanup(*ctx);
      }
      else
          *ctx = (EVP_AEAD_CTX *)malloc(sizeof(EVP_AEAD_CTX));
  
      EVP_AEAD_CTX_init(*ctx, aead_, key, key_len, auth_tag_size, NULL);
      if (key_copy)
          memcpy(key_copy, key, key_len);
  }
  
  
  static int
  determine_diversification_key (enc_session_t *enc_session_p,
                                            uint8_t *diversification_nonce)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      const int is_client = !(enc_session->es_flags & ES_SERVER);
      EVP_AEAD_CTX **ctx_s_key;
      unsigned char *key_i, *iv;
      const size_t iv_len = enc_session->es_flags & ES_GQUIC2
                                              ? IQUIC_IV_LEN : aes128_iv_len;
      uint8_t ikm[aes128_key_len + MAX_IV_LEN];
      char str_buf[DNONC_LENGTH * 2 + 1];
  
      if (is_client)
      {
          ctx_s_key = &enc_session->dec_ctx_i;
          key_i = enc_session->dec_key_i;
          iv = enc_session->dec_key_nonce_i;
      }
      else
      {
          ctx_s_key = &enc_session->enc_ctx_i;
          key_i = enc_session->enc_key_i;
          iv = enc_session->enc_key_nonce_i;
      }
      memcpy(ikm, key_i, aes128_key_len);
      memcpy(ikm + aes128_key_len, iv, iv_len);
      lsquic_export_key_material(ikm, aes128_key_len + iv_len,
                          diversification_nonce, DNONC_LENGTH,
                          (const unsigned char *) "QUIC key diversification", 24,
                          0, NULL, aes128_key_len, key_i, 0, NULL,
                          iv_len, iv, NULL, NULL, NULL);
  
      setup_aead_ctx(enc_session, ctx_s_key, key_i, aes128_key_len, NULL);
      if (enc_session->es_flags & ES_LOG_SECRETS)
      {
          LSQ_DEBUG("determine_diversification_keys nonce: %s",
              HEXSTR(diversification_nonce, DNONC_LENGTH, str_buf));
          LSQ_DEBUG("determine_diversification_keys diversification key: %s",
              HEXSTR(key_i, aes128_key_len, str_buf));
          LSQ_DEBUG("determine_diversification_keys diversification iv: %s",
              HEXSTR(iv, iv_len, str_buf));
      }
      return 0;
  }
  
  
  /* After CHLO msg generatered, call it to determine_keys */
  static void
  determine_keys (struct lsquic_enc_session *enc_session)
  {
      lsquic_str_t *chlo = &enc_session->chlo;
      const int is_client = !(enc_session->es_flags & ES_SERVER);
      uint8_t shared_key_c[32];
      const size_t iv_len = enc_session->es_flags & ES_GQUIC2
                                              ? IQUIC_IV_LEN : aes128_iv_len;
      unsigned char *nonce_c;
      unsigned char *hkdf_input, *hkdf_input_p;
  
      unsigned char c_key[aes128_key_len];
      unsigned char s_key[aes128_key_len];
      unsigned char *c_key_bin = NULL;
      unsigned char *s_key_bin = NULL;
  
      unsigned char *c_iv;
      unsigned char *s_iv;
      uint8_t *c_hp, *s_hp;
      size_t nonce_len, hkdf_input_len;
      unsigned char sub_key[32];
      EVP_AEAD_CTX **ctx_c_key, **ctx_s_key;
      char key_flag;
      char str_buf[512];
  
      hkdf_input_len = (enc_session->have_key == 0 ? 18 + 1 : 33 + 1)
          + enc_session->cid.len
          + lsquic_str_len(chlo)
          + (is_client
                  ? lsquic_str_len(&enc_session->info->scfg)
                  : (size_t) enc_session->server_config->lsc_scfg->info.scfg_len)
          + lsquic_str_len(enc_session->cert_ptr);
      hkdf_input = malloc(hkdf_input_len);
      if (UNLIKELY(!hkdf_input))
      {
          LSQ_WARN("cannot allocate memory for hkdf_input");
          return;
      }
      hkdf_input_p = hkdf_input;
  
      if (enc_session->have_key == 0)
      {
          memcpy(hkdf_input_p, "QUIC key expansion\0", 18 + 1); /* Add a 0x00 */
          hkdf_input_p += 18 + 1;
          key_flag = 'I';
      }
      else
      {
          memcpy(hkdf_input_p, "QUIC forward secure key expansion\0", 33 + 1); /* Add a 0x00 */
          hkdf_input_p += 33 + 1;
          key_flag = 'F';
      }
  
      lsquic_c255_gen_share_key(enc_session->priv_key,
                         enc_session->hs_ctx.pubs,
                         (unsigned char *)shared_key_c);
      if (is_client)
      {
          if (enc_session->have_key == 0)
          {
              ctx_c_key = &enc_session->enc_ctx_i;
              ctx_s_key = &enc_session->dec_ctx_i;
              c_iv = (unsigned char *) enc_session->enc_key_nonce_i;
              s_iv = (unsigned char *) enc_session->dec_key_nonce_i;
              c_key_bin = enc_session->enc_key_i;
              s_key_bin = enc_session->dec_key_i;
              c_hp = enc_session->es_flags & ES_GQUIC2
                                  ? enc_session->es_hps[GEL_EARLY][0] : NULL;
              s_hp = enc_session->es_flags & ES_GQUIC2
                                  ? enc_session->es_hps[GEL_EARLY][1] : NULL;
          }
          else
          {
              ctx_c_key = &enc_session->enc_ctx_f;
              ctx_s_key = &enc_session->dec_ctx_f;
              c_iv = (unsigned char *) enc_session->enc_key_nonce_f;
              s_iv = (unsigned char *) enc_session->dec_key_nonce_f;
              c_hp = enc_session->es_flags & ES_GQUIC2
                                  ? enc_session->es_hps[GEL_FORW][0] : NULL;
              s_hp = enc_session->es_flags & ES_GQUIC2
                                  ? enc_session->es_hps[GEL_FORW][1] : NULL;
          }
      }
      else
      {
          if (enc_session->have_key == 0)
          {
              ctx_c_key = &enc_session->dec_ctx_i;
              ctx_s_key = &enc_session->enc_ctx_i;
              c_iv = (unsigned char *) enc_session->dec_key_nonce_i;
              s_iv = (unsigned char *) enc_session->enc_key_nonce_i;
              c_key_bin = enc_session->dec_key_i;
              s_key_bin = enc_session->enc_key_i;
              c_hp = enc_session->es_flags & ES_GQUIC2
                                  ? enc_session->es_hps[GEL_EARLY][1] : NULL;
              s_hp = enc_session->es_flags & ES_GQUIC2
                                  ? enc_session->es_hps[GEL_EARLY][0] : NULL;
          }
          else
          {
              ctx_c_key = &enc_session->dec_ctx_f;
              ctx_s_key = &enc_session->enc_ctx_f;
              c_iv = (unsigned char *) enc_session->dec_key_nonce_f;
              s_iv = (unsigned char *) enc_session->enc_key_nonce_f;
              c_hp = enc_session->es_flags & ES_GQUIC2
                                  ? enc_session->es_hps[GEL_FORW][1] : NULL;
              s_hp = enc_session->es_flags & ES_GQUIC2
                                  ? enc_session->es_hps[GEL_FORW][0] : NULL;
          }
      }
  
      LSQ_DEBUG("export_key_material lsquic_c255_gen_share_key %s",
                lsquic_get_bin_str(shared_key_c, 32, 512));
  
      memcpy(hkdf_input_p, enc_session->cid.idbuf, enc_session->cid.len);
      hkdf_input_p += enc_session->cid.len;
      memcpy(hkdf_input_p, lsquic_str_cstr(chlo), lsquic_str_len(chlo)); /* CHLO msg */
      hkdf_input_p += lsquic_str_len(chlo);
      if (is_client)
      {
          memcpy(hkdf_input_p, lsquic_str_cstr(&enc_session->info->scfg),
                         lsquic_str_len(&enc_session->info->scfg)); /* scfg msg */
          hkdf_input_p += lsquic_str_len(&enc_session->info->scfg);
      }
      else
      {
          memcpy(hkdf_input_p,
                  (const char *) enc_session->server_config->lsc_scfg->scfg,
                         enc_session->server_config->lsc_scfg->info.scfg_len);
          hkdf_input_p += enc_session->server_config->lsc_scfg->info.scfg_len;
      }
      memcpy(hkdf_input_p, lsquic_str_cstr(enc_session->cert_ptr),
                     lsquic_str_len(enc_session->cert_ptr));
      assert(hkdf_input + hkdf_input_len
                  == hkdf_input_p + lsquic_str_len(enc_session->cert_ptr));
      LSQ_DEBUG("export_key_material hkdf_input %s",
                HEXSTR(hkdf_input, hkdf_input_len, str_buf));
  
      /* then need to use the salts and the shared_key_* to get the real aead key */
      nonce_len = sizeof(enc_session->hs_ctx.nonc)
                                              + lsquic_str_len(&enc_session->ssno);
      nonce_c = malloc(nonce_len);
      if (UNLIKELY(!nonce_c))
      {
          LSQ_WARN("cannot allocate memory for nonce_c");
          free(hkdf_input);
          return;
      }
      memcpy(nonce_c, enc_session->hs_ctx.nonc, sizeof(enc_session->hs_ctx.nonc));
      memcpy(nonce_c + sizeof(enc_session->hs_ctx.nonc),
          lsquic_str_cstr(&enc_session->ssno),
          lsquic_str_len(&enc_session->ssno));
  
      LSQ_DEBUG("export_key_material nonce %s",
                    HEXSTR(nonce_c, nonce_len, str_buf));
  
      lsquic_export_key_material(shared_key_c, 32,
                          nonce_c, nonce_len,
                          hkdf_input, hkdf_input_len,
                          aes128_key_len, c_key,
                          aes128_key_len, s_key,
                          iv_len, c_iv,
                          iv_len, s_iv,
                          sub_key,
                          c_hp, s_hp
                          );
  
      setup_aead_ctx(enc_session, ctx_c_key, c_key, aes128_key_len, c_key_bin);
      setup_aead_ctx(enc_session, ctx_s_key, s_key, aes128_key_len, s_key_bin);
  
      free(nonce_c);
      free(hkdf_input);
  
      if (enc_session->es_flags & ES_LOG_SECRETS)
      {
          LSQ_DEBUG("***export_key_material '%c' c_key: %s", key_flag,
                    HEXSTR(c_key, aes128_key_len, str_buf));
          LSQ_DEBUG("***export_key_material '%c' s_key: %s", key_flag,
                    HEXSTR(s_key, aes128_key_len, str_buf));
          LSQ_DEBUG("***export_key_material '%c' c_iv: %s", key_flag,
                    HEXSTR(c_iv, iv_len, str_buf));
          LSQ_DEBUG("***export_key_material '%c' s_iv: %s", key_flag,
                    HEXSTR(s_iv, iv_len, str_buf));
          LSQ_DEBUG("***export_key_material '%c' subkey: %s", key_flag,
                    HEXSTR(sub_key, 32, str_buf));
          if (c_hp)
              LSQ_DEBUG("***export_key_material '%c' c_hp: %s", key_flag,
                    HEXSTR(c_hp, IQUIC_HP_LEN, str_buf));
          if (s_hp)
              LSQ_DEBUG("***export_key_material '%c' s_hp: %s", key_flag,
                    HEXSTR(s_hp, IQUIC_HP_LEN, str_buf));
      }
  }
  
  
  /* 0 Match */
  static int cached_certs_match(c_cert_item_t *item,
                                          lsquic_str_t **certs, int count)
  {
      int i;
      if (!item || item->count != count)
          return -1;
  
      for (i=0; i<count; ++i)
      {
          if (lsquic_str_bcmp(certs[i], &item->crts[i]) != 0)
              return -1;
      }
  
      return 0;
  }
  
  
  static const char *
  he2str (enum handshake_error he)
  {
      switch (he)
      {
      case DATA_NOT_ENOUGH:   return "DATA_NOT_ENOUGH";
      case HS_ERROR:          return "HS_ERROR";
      case HS_SHLO:           return "HS_SHLO";
      case HS_1RTT:           return "HS_1RTT";
      case HS_SREJ:           return "HS_SREJ";
      default:
          assert(0);          return "<unknown enum value>";
      }
  }
  
  
  /* NOT packet, just the frames-data */
  /* return rtt number:
   *      0 OK
   *      DATA_NOT_ENOUGH(-2) for not enough data,
   *      DATA_FORMAT_ERROR(-1) all other errors
   */
  static int
  lsquic_enc_session_handle_chlo_reply (enc_session_t *enc_session_p,
                                                  const uint8_t *data, int len)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      uint32_t head_tag;
      int ret, got_srej;
      lsquic_session_cache_info_t *info = enc_session->info;
      c_cert_item_t *cert_item = enc_session->cert_item;
  
      /* FIXME get the number first */
      lsquic_str_t **out_certs = NULL;
      size_t out_certs_count = 0, i;
  
      ret = parse_hs(enc_session, data, len, &head_tag);
      if (ret)
          goto end;
  
      got_srej = head_tag == QTAG_SREJ;
      switch (head_tag)
      {
      case QTAG_SREJ:
          if (enc_session->es_flags & ES_RECV_SREJ)
          {
              LSQ_DEBUG("received second SREJ: handshake failed");
              ret = -1;
              goto end;
          }
          enc_session->es_flags |= ES_RECV_SREJ;
          /* fall-through */
      case QTAG_REJ:
          enc_session->hsk_state = HSK_CHLO_REJ;
          enc_session->es_flags |= ES_RECV_REJ;
          break;
      case QTAG_SHLO:
          enc_session->hsk_state = HSK_COMPLETED;
          EV_LOG_HSK_COMPLETED(&enc_session->cid);
          if (!(enc_session->es_flags & ES_RECV_REJ))
              EV_LOG_SESSION_RESUMPTION(&enc_session->cid);
          break;
      default:
          ret = 1;    /* XXX Why 1? */
          goto end;
      }
  
      if (info->scfg_flag == 1)
      {
          ret = parse_hs(enc_session, (uint8_t *)lsquic_str_cstr(&info->scfg),
                         lsquic_str_len(&info->scfg), &head_tag);
  
          /* After handled, set the length to 0 to avoid do it again*/
          enc_session->info->scfg_flag = 2;
          if (ret)
              goto end;
  
          if (got_srej)
          {
              if (lsquic_str_len(&enc_session->info->sstk))
                  ret = HS_SREJ;
              else
              {
                  LSQ_DEBUG("expected STK in SREJ message from the server");
                  ret = -1;
              }
              goto end;
          }
  
          if (enc_session->hs_ctx.ccert)
          {
              out_certs_count = lsquic_get_certs_count(enc_session->hs_ctx.ccert);
              if (out_certs_count > 0)
              {
                  out_certs = malloc(out_certs_count * sizeof(lsquic_str_t *));
                  if (!out_certs)
                  {
                      ret = -1;
                      goto end;
                  }
  
                  for (i=0; i<out_certs_count; ++i)
                      out_certs[i] = lsquic_str_new(NULL, 0);
  
                  ret = handle_chlo_reply_verify_prof(enc_session, out_certs,
                                              &out_certs_count,
                                              (cert_item ? cert_item->crts : NULL),
                                              (cert_item ? cert_item->count : 0));
                  if (ret == 0)
                  {
                      if (out_certs_count > 0)
                      {
                          if (cached_certs_match(cert_item, out_certs,
                                                          out_certs_count) != 0)
                          {
                              cert_item = make_c_cert_item(out_certs,
                                                              out_certs_count);
                              enc_session->cert_item = cert_item;
                              enc_session->cert_ptr = &cert_item->crts[0];
                          }
                      }
                  }
                  for (i=0; i<out_certs_count; ++i)
                      lsquic_str_delete(out_certs[i]);
                  free(out_certs);
  
                  if (ret)
                      goto end;
              }
          }
      }
  
      if (enc_session->hsk_state == HSK_COMPLETED)
      {
          determine_keys(enc_session);
          enc_session->have_key = 3;
      }
  
    end:
      LSQ_DEBUG("lsquic_enc_session_handle_chlo_reply called, buf in %d, return %d.", len, ret);
      EV_LOG_CONN_EVENT(&enc_session->cid, "%s returning %s", __func__,
                                                                  he2str(ret));
      return ret;
  }
  
  
  /** stk = 16 bytes IP ( V4 is 4 bytes, will add 12 byes 0 )
   *      + 8 bytes time
   *      + 36 bytes random bytes (24 bytes can be reserved for other using)
   *  then stk first 48 byte will be encrypted with AES128-GCM
   *  when encrypting, the salt is the last 12 bytes
   */
  #ifdef NDEBUG
  static
  #endif
  void
  lsquic_gen_stk (lsquic_server_config_t *server_config, const struct sockaddr *ip_addr,
           uint64_t tm, unsigned char stk_out[STK_LENGTH])
  {
      unsigned char stk[STK_LENGTH + 16];
      size_t out_len = STK_LENGTH + 16;
  
      memset(stk, 0 , 24);
      if (AF_INET == ip_addr->sa_family)
          memcpy(stk, &((struct sockaddr_in *)ip_addr)->sin_addr.s_addr, 4);
      else
          memcpy(stk, &((struct sockaddr_in6 *)ip_addr)->sin6_addr, 16);
      memcpy(stk + 16, &tm, 8);
      RAND_bytes(stk + 24, STK_LENGTH - 24 - 12);
      RAND_bytes(stk_out + STK_LENGTH - 12, 12);
      lsquic_aes_aead_enc(&server_config->lsc_stk_ctx, NULL, 0, stk_out + STK_LENGTH - 12, 12, stk,
                   STK_LENGTH - 12 - 12, stk_out, &out_len);
  }
  
  
  /* server using */
  #ifdef NDEBUG
  static
  #endif
  enum hsk_failure_reason
  lsquic_verify_stk0 (const struct lsquic_enc_session *enc_session,
               lsquic_server_config_t *server_config,
               const struct sockaddr *ip_addr, uint64_t tm, lsquic_str_t *stk,
               unsigned secs_since_stk_generated)
  {
      uint64_t tm0, exp;
      unsigned char *const stks = (unsigned char *) lsquic_str_buf(stk);
      unsigned char stk_out[STK_LENGTH];
      size_t out_len = STK_LENGTH;
  
      if (lsquic_str_len(stk) < STK_LENGTH)
          return HFR_SRC_ADDR_TOKEN_INVALID;
  
      int ret = lsquic_aes_aead_dec(&server_config->lsc_stk_ctx, NULL, 0,
                             stks + STK_LENGTH - 12, 12, stks,
                             STK_LENGTH - 12, stk_out, &out_len);
      if (ret != 0)
      {
          LSQ_DEBUG("***lsquic_verify_stk decrypted failed.");
          return HFR_SRC_ADDR_TOKEN_DECRYPTION;
      }
  
      if (AF_INET == ip_addr->sa_family)
      {
          if (memcmp(stk_out, &((struct sockaddr_in *)ip_addr)->sin_addr.s_addr, 4) != 0)
          {
              LSQ_DEBUG("***lsquic_verify_stk for ipv4 failed.");
              return HFR_SRC_ADDR_TOKEN_DIFFERENT_IP_ADDRESS;
          }
      }
      else
      {
          if (memcmp(stk_out, &((struct sockaddr_in6 *)ip_addr)->sin6_addr, 16) != 0)
          {
              LSQ_DEBUG("***lsquic_verify_stk for ipv6 failed.");
              return HFR_SRC_ADDR_TOKEN_DIFFERENT_IP_ADDRESS;
          }
      }
  
      memcpy((void *)&tm0, stk_out + 16, 8);
      if (tm < tm0)
      {
          LSQ_DEBUG("***lsquic_verify_stk timestamp is in the future.");
          return HFR_SRC_ADDR_TOKEN_CLOCK_SKEW;
      }
  
      if (secs_since_stk_generated)
          exp = tm0 + secs_since_stk_generated;
      else
          exp = server_config->lsc_scfg->info.expy;
  
      if (tm > server_config->lsc_scfg->info.expy /* XXX this check does not seem needed */ ||
                                                          tm0 > exp)
      {
          LSQ_DEBUG("***lsquic_verify_stk stk expired");
          return HFR_SRC_ADDR_TOKEN_EXPIRED;
      }
  
      LSQ_DEBUG("***lsquic_verify_stk pass.");
      return HFR_HANDSHAKE_OK;
  }
  
  
  /* 0, verified, other fail */
  #ifdef NDEBUG
  static
  #endif
  enum hsk_failure_reason
  lsquic_verify_stk (enc_session_t *enc_session_p,
                 const struct sockaddr *ip_addr, uint64_t tm, lsquic_str_t *stk)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      if (lsquic_str_len(&enc_session->sstk) > 0)
      {
          ESHIST_APPEND(enc_session, ESHE_HAS_SSTK);
          if (0 == lsquic_str_bcmp(&enc_session->sstk, &enc_session->hs_ctx.stk))
              return HFR_HANDSHAKE_OK;
          else
              return HFR_SRC_ADDR_TOKEN_INVALID;
      }
      else
          return lsquic_verify_stk0(enc_session, enc_session->server_config,
                                                          ip_addr, tm, stk, 0);
  }
  
  
  static uint64_t combine_path_id_pack_num(uint8_t path_id, uint64_t pack_num)
  {
      uint64_t v = ((uint64_t)path_id << 56) | pack_num;
      return v;
  }
  
  
  #   define IS_SERVER(session) ((session)->es_flags & ES_SERVER)
  
  static int
  verify_packet_hash (const struct lsquic_enc_session *enc_session,
      enum lsquic_version version, const unsigned char *buf, size_t *header_len,
      size_t data_len, unsigned char *buf_out, size_t max_out_len,
      size_t *out_len)
  {
      uint8_t md[HS_PKT_HASH_LENGTH];
      uint128 hash;
      int ret;
  
      if (data_len < HS_PKT_HASH_LENGTH)
          return -1;
  
      if (!enc_session || (IS_SERVER(enc_session)))
          hash = lsquic_fnv1a_128_3(buf, *header_len,
                      buf + *header_len + HS_PKT_HASH_LENGTH,
                      data_len - HS_PKT_HASH_LENGTH,
                      (unsigned char *) "Client", 6);
      else
          hash = lsquic_fnv1a_128_3(buf, *header_len,
                      buf + *header_len + HS_PKT_HASH_LENGTH,
                      data_len - HS_PKT_HASH_LENGTH,
                      (unsigned char *) "Server", 6);
  
      lsquic_serialize_fnv128_short(hash, md);
      ret = memcmp(md, buf + *header_len, HS_PKT_HASH_LENGTH);
      if(ret == 0)
      {
          *header_len += HS_PKT_HASH_LENGTH;
          *out_len = data_len - HS_PKT_HASH_LENGTH;
          if (max_out_len < *header_len + *out_len)
              return -1;
  
          memcpy(buf_out, buf, *header_len + *out_len);
          return 0;
      }
      else
          return -1;
  }
  
  
  static enum enc_level
  decrypt_packet (struct lsquic_enc_session *enc_session, uint8_t path_id,
                  uint64_t pack_num, unsigned char *buf, size_t *header_len,
                  size_t data_len, unsigned char *buf_out, size_t max_out_len,
                  size_t *out_len)
  {
      int ret;
      /* Comment: 12 = sizeof(dec_key_iv] 4 + sizeof(pack_num) 8 */
      uint8_t nonce[12];
      uint64_t path_id_packet_number;
      EVP_AEAD_CTX *key = NULL;
      int try_times = 0;
      enum enc_level enc_level;
  
      path_id_packet_number = combine_path_id_pack_num(path_id, pack_num);
      memcpy(buf_out, buf, *header_len);
      do
      {
          if (enc_session->have_key == 3 && try_times == 0)
          {
              key = enc_session->dec_ctx_f;
              memcpy(nonce, enc_session->dec_key_nonce_f, 4);
              LSQ_DEBUG("decrypt_packet using 'F' key...");
              enc_level = ENC_LEV_FORW;
          }
          else
          {
              key = enc_session->dec_ctx_i;
              memcpy(nonce, enc_session->dec_key_nonce_i, 4);
              LSQ_DEBUG("decrypt_packet using 'I' key...");
              enc_level = ENC_LEV_INIT;
          }
          memcpy(nonce + 4, &path_id_packet_number,
                 sizeof(path_id_packet_number));
  
          *out_len = data_len;
          ret = lsquic_aes_aead_dec(key,
                             buf, *header_len,
                             nonce, 12,
                             buf + *header_len, data_len,
                             buf_out + *header_len, out_len);
  
          if (ret != 0)
              ++try_times;
          else
          {
              if (enc_session->peer_have_final_key == 0 &&
                  enc_session->have_key == 3 &&
                  try_times == 0)
              {
                  LSQ_DEBUG("!!!decrypt_packet find peer have final key.");
                  enc_session->peer_have_final_key = 1;
                  EV_LOG_CONN_EVENT(&enc_session->cid, "settled on private key "
                      "'%c' after %d tries (packet number %"PRIu64")",
                      key == enc_session->dec_ctx_f ? 'F' : 'I',
                      try_times, pack_num);
              }
              break;
          }
      }
      while (try_times < 2);
  
      LSQ_DEBUG("***decrypt_packet %s.", (ret == 0 ? "succeed" : "failed"));
      return ret == 0 ? enc_level : (enum enc_level) -1;
  }
  
  
  static int
  lsquic_enc_session_have_key_gt_one (enc_session_t *enc_session_p)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      return enc_session && enc_session->have_key > 1;
  }
  
  
  /* The size of `buf' is *header_len plus data_len.  The two parts of the
   * buffer correspond to the header and the payload of incoming QUIC packet.
   */
  static enum enc_level
  lsquic_enc_session_decrypt (struct lsquic_enc_session *enc_session,
                 enum lsquic_version version,
                 uint8_t path_id, uint64_t pack_num,
                 unsigned char *buf, size_t *header_len, size_t data_len,
                 unsigned char *diversification_nonce,
                 unsigned char *buf_out, size_t max_out_len, size_t *out_len)
  {
      /* Client: got SHLO which should have diversification_nonce */
      if (diversification_nonce && enc_session && enc_session->have_key == 1)
      {
          determine_diversification_key(enc_session, diversification_nonce);
          enc_session->have_key = 2;
      }
  
      if (lsquic_enc_session_have_key_gt_one(enc_session))
          return decrypt_packet(enc_session, path_id, pack_num, buf,
                          header_len, data_len, buf_out, max_out_len, out_len);
      else if (0 == verify_packet_hash(enc_session, version, buf, header_len,
                                       data_len, buf_out, max_out_len, out_len))
          return ENC_LEV_CLEAR;
      else
          return -1;
  }
  
  
  static enum dec_packin
  gquic_decrypt_packet (enc_session_t *enc_session_p,
                              struct lsquic_engine_public *enpub,
                              const struct lsquic_conn *lconn,
                              struct lsquic_packet_in *packet_in)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      size_t header_len, data_len;
      enum enc_level enc_level;
      size_t out_len = 0;
      unsigned char *copy = lsquic_mm_get_packet_in_buf(&enpub->enp_mm, 1370);
      if (!copy)
      {
          LSQ_WARN("cannot allocate memory to copy incoming packet data");
          return DECPI_NOMEM;
      }
  
      assert(packet_in->pi_data);
      header_len = packet_in->pi_header_sz;
      data_len   = packet_in->pi_data_sz - packet_in->pi_header_sz;
      enc_level = lsquic_enc_session_decrypt(enc_session,
                          lconn->cn_version, 0,
                          packet_in->pi_packno, packet_in->pi_data,
                          &header_len, data_len,
                          lsquic_packet_in_nonce(packet_in),
                          copy, 1370, &out_len);
      if ((enum enc_level) -1 == enc_level)
      {
          lsquic_mm_put_packet_in_buf(&enpub->enp_mm, copy, 1370);
          EV_LOG_CONN_EVENT(&lconn->cn_cid, "could not decrypt packet %"PRIu64,
                                                          packet_in->pi_packno);
          return DECPI_BADCRYPT;
      }
  
      assert(header_len + out_len <= 1370);
      if (packet_in->pi_flags & PI_OWN_DATA)
          lsquic_mm_put_packet_in_buf(&enpub->enp_mm, packet_in->pi_data, 1370);
      packet_in->pi_data = copy;
      packet_in->pi_flags |= PI_OWN_DATA | PI_DECRYPTED
                          | (enc_level << PIBIT_ENC_LEV_SHIFT);
      packet_in->pi_header_sz = header_len;
      packet_in->pi_data_sz   = out_len + header_len;
      EV_LOG_CONN_EVENT(&lconn->cn_cid, "decrypted packet %"PRIu64,
                                                      packet_in->pi_packno);
      return DECPI_OK;
  }
  
  
  static enum enc_level
  gquic_encrypt_buf (struct lsquic_enc_session *enc_session,
                 enum lsquic_version version,
                 uint8_t path_id, uint64_t pack_num,
                 const unsigned char *header, size_t header_len,
                 const unsigned char *data, size_t data_len,
                 unsigned char *buf_out, size_t max_out_len, size_t *out_len,
                 int is_hello)
  {
      uint8_t md[HS_PKT_HASH_LENGTH];
      uint128 hash;
      int ret;
      enum enc_level enc_level;
      int is_chlo = (is_hello && ((IS_SERVER(enc_session)) == 0));
      int is_shlo = (is_hello && (IS_SERVER(enc_session)));
  
      /* Comment: 12 = sizeof(dec_key_iv] 4 + sizeof(pack_num) 8 */
      uint8_t nonce[12];
      uint64_t path_id_packet_number;
      EVP_AEAD_CTX *key;
  
      if (enc_session)
          LSQ_DEBUG("%s: hsk_state: %d", __func__, enc_session->hsk_state);
      else
          LSQ_DEBUG("%s: enc_session is not set", __func__);
  
      if (!enc_session || enc_session->have_key == 0 || is_chlo)
      {
          *out_len = header_len + data_len + HS_PKT_HASH_LENGTH;
          if (max_out_len < *out_len)
              return -1;
  
          if (!enc_session || (IS_SERVER(enc_session)))
              hash = lsquic_fnv1a_128_3(header, header_len, data, data_len,
                                          (unsigned char *) "Server", 6);
          else
              hash = lsquic_fnv1a_128_3(header, header_len, data, data_len,
                                          (unsigned char *) "Client", 6);
  
          lsquic_serialize_fnv128_short(hash, md);
          memcpy(buf_out, header, header_len);
          memcpy(buf_out + header_len, md, HS_PKT_HASH_LENGTH);
          memcpy(buf_out + header_len + HS_PKT_HASH_LENGTH, data, data_len);
          return ENC_LEV_CLEAR;
      }
      else
      {
          if (enc_session->have_key != 3 || is_shlo ||
              ((IS_SERVER(enc_session)) &&
               enc_session->server_start_use_final_key == 0))
          {
              LSQ_DEBUG("lsquic_enc_session_encrypt using 'I' key...");
              key = enc_session->enc_ctx_i;
              memcpy(nonce, enc_session->enc_key_nonce_i, 4);
              if (is_shlo && enc_session->have_key == 3)
              {
                  enc_session->server_start_use_final_key = 1;
              }
              enc_level = ENC_LEV_INIT;
          }
          else
          {
              LSQ_DEBUG("lsquic_enc_session_encrypt using 'F' key...");
              key = enc_session->enc_ctx_f;
              memcpy(nonce, enc_session->enc_key_nonce_f, 4);
              enc_level = ENC_LEV_FORW;
          }
          path_id_packet_number = combine_path_id_pack_num(path_id, pack_num);
          memcpy(nonce + 4, &path_id_packet_number,
                 sizeof(path_id_packet_number));
  
          memcpy(buf_out, header, header_len);
          *out_len = max_out_len - header_len;
  
          ret = lsquic_aes_aead_enc(key, header, header_len, nonce, 12, data,
                             data_len, buf_out + header_len, out_len);
          if (ret == 0)
          {
              *out_len += header_len;
              return enc_level;
          }
          else
              return -1;
      }
  }
  
  
  /* server */
  /* out_len should have init value as the max length of out */
  /* return -1 error, 0, SHLO, 1, RTT1, 2, RTT2, DELAYED */
  static enum handshake_error
  lsquic_enc_session_handle_chlo(enc_session_t *enc_session_p,
                                   enum lsquic_version version,
                                   const uint8_t *in, int in_len, time_t t,
                                   const struct sockaddr *peer,
                                   const struct sockaddr *local,
                                   uint8_t *out, size_t *out_len,
                                   uint8_t nonce[DNONC_LENGTH], int *nonce_set)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      enum handshake_error rtt;
      int len;
      lsquic_server_config_t *server_config;
      const struct lsquic_engine_public *const enpub = enc_session->enpub;
      const struct lsquic_shared_hash_if *const shi = enpub->enp_shi;
      void *const shi_ctx = enpub->enp_shi_ctx;
  
      server_config = get_valid_scfg(enc_session, enpub);
      if (!server_config)
          return HS_ERROR;
      assert(server_config->lsc_scfg);
  
      enc_session->server_config = server_config;
  
      *nonce_set = 0;
      rtt = handle_chlo_frames_data(in, in_len, enc_session,
                      enpub->enp_lookup_cert, enpub->enp_cert_lu_ctx,
                      local, shi, shi_ctx, peer, t);
      if (rtt == HS_1RTT)
      {
  
          LSQ_DEBUG("lsquic_enc_session_handle_chlo call gen_rej1_data");
          len = gen_rej1_data(enc_session, out, *out_len, peer, t);
          if (len < 0)
          {
              rtt = HS_ERROR;
              goto end;
          }
          *out_len = len;
      }
      else if (rtt == HS_SHLO)
      {
          enc_session->have_key = 0;
          determine_keys(enc_session);
          enc_session->have_key = 1;
  
          if (lsquic_str_len(&enc_session->hs_ctx.stk) > 0)
          {
              shi->shi_delete(shi_ctx, lsquic_str_cstr(&enc_session->hs_ctx.stk),
                              lsquic_str_len(&enc_session->hs_ctx.stk));
          }
  
          LSQ_DEBUG("lsquic_enc_session_handle_chlo call gen_shlo_data");
          len = gen_shlo_data(out, *out_len, enc_session, version, peer,
                                                                      t, nonce);
          if (len < 0)
          {
              rtt = HS_ERROR;
              goto end;
          }
          *out_len = len;
          *nonce_set = 1;
  
          determine_diversification_key(enc_session, nonce);
          enc_session->have_key = 2;
          determine_keys(enc_session);
          enc_session->have_key = 3;
  
          enc_session->hsk_state = HSK_COMPLETED;
          LSQ_DEBUG("lsquic_enc_session_handle_chlo have_key 3 hsk_state HSK_COMPLETED.");
      }
  
    end:
      EV_LOG_CONN_EVENT(&enc_session->cid, "%s returning %s", __func__,
                                                              he2str(rtt));
      return rtt;
  }
  
  
  static int
  lsquic_enc_session_get_peer_option (enc_session_t *enc_session_p,
                                                                  uint32_t tag)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      switch (tag)
      {
      case QTAG_NSTP:
          return !!(enc_session->hs_ctx.opts & HOPT_NSTP);
      case QTAG_SREJ:
          return !!(enc_session->hs_ctx.opts & HOPT_SREJ);
      default:
          assert(0);
          return 0;
      }
  }
  
  
  /* Query a several parameters sent by the peer that are required by
   * connection.
   */
  static int
  lsquic_enc_session_get_peer_setting (enc_session_t *enc_session_p,
                                          uint32_t tag, uint32_t *val)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      switch (tag)
      {
      case QTAG_TCID:
          if (enc_session->hs_ctx.set & HSET_TCID)
          {
              *val = enc_session->hs_ctx.tcid;
              return 0;
          }
          else
              return -1;
      case QTAG_SMHL:
          if (enc_session->hs_ctx.set & HSET_SMHL)
          {
              *val = enc_session->hs_ctx.smhl;
              return 0;
          }
          else
              return -1;
      case QTAG_IRTT:
          if (enc_session->hs_ctx.set & HSET_IRTT)
          {
              *val = enc_session->hs_ctx.irtt;
              return 0;
          }
          else
              return -1;
      }
  
      /* XXX For the following values, there is no record which were present
       *     in CHLO or SHLO and which were not.  Assume that zero means that
       *     they weren't present.
       */
      if (IS_SERVER(enc_session))
          switch (tag)
          {
          case QTAG_CFCW:
              if (enc_session->hs_ctx.scfcw)
              {
                  *val = enc_session->hs_ctx.scfcw;
                  return 0;
              }
              else
                  return -1;
          case QTAG_SFCW:
              if (enc_session->hs_ctx.ssfcw)
              {
                  *val = enc_session->hs_ctx.ssfcw;
                  return 0;
              }
              else
                  return -1;
          case QTAG_MIDS:
              if (enc_session->hs_ctx.smids)
              {
                  *val = enc_session->hs_ctx.smids;
                  return 0;
              }
              else
                  return -1;
          default:
              return -1;
          }
      else
          switch (tag)
          {
          case QTAG_CFCW:
              if (enc_session->hs_ctx.cfcw)
              {
                  *val = enc_session->hs_ctx.cfcw;
                  return 0;
              }
              else
                  return -1;
          case QTAG_SFCW:
              if (enc_session->hs_ctx.sfcw)
              {
                  *val = enc_session->hs_ctx.sfcw;
                  return 0;
              }
              else
                  return -1;
          case QTAG_MIDS:
              if (enc_session->hs_ctx.mids)
              {
                  *val = enc_session->hs_ctx.mids;
                  return 0;
              }
              else
                  return -1;
          default:
              return -1;
          }
  }
  
  
  static const char *
  lsquic_enc_session_cipher (enc_session_t *enc_session_p)
  {
      return LN_aes_128_gcm; /* TODO: get this string from enc_session */
  }
  
  
  static int
  lsquic_enc_session_keysize (enc_session_t *enc_session_p)
  {
      return 128 /* bits */ / 8; /* TODO: get this info from enc_session */
  }
  
  
  static int
  lsquic_enc_session_alg_keysize (enc_session_t *enc_session_p)
  {
      return 16; /* TODO: get this info from enc_session */
  }
  
  
  #if LSQUIC_KEEP_ENC_SESS_HISTORY
  static void
  lsquic_get_enc_hist (enc_session_t *enc_session_p,
                                          char buf[(1 << ESHIST_BITS) + 1])
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      const unsigned hist_idx = ESHIST_MASK & enc_session->es_hist_idx;
      if (enc_session->es_hist_buf[hist_idx] == ESHE_EMPTY)
          memcpy(buf, enc_session->es_hist_buf, hist_idx + 1);
      else
      {
          memcpy(buf, enc_session->es_hist_buf + hist_idx, sizeof(enc_session->es_hist_buf) - hist_idx);
          memcpy(buf + hist_idx, enc_session->es_hist_buf, hist_idx);
          buf[(1 << ESHIST_BITS)] = '\0';
      }
  }
  
  
  #endif
  
  
  static const char *
  lsquic_enc_session_get_ua (enc_session_t *enc_session_p)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      if (enc_session && lsquic_str_len(&enc_session->hs_ctx.uaid) > 0)
          return lsquic_str_buf(&enc_session->hs_ctx.uaid);
      else
          return NULL;
  }
  
  
  static const char *
  lsquic_enc_session_get_sni (enc_session_t *enc_session_p)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      return lsquic_str_cstr(&enc_session->hs_ctx.sni);
  }
  
  
  #ifndef NDEBUG
  static uint8_t
  lsquic_enc_session_have_key (enc_session_t *enc_session_p)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      return enc_session->have_key;
  }
  
  
  static void
  lsquic_enc_session_set_have_key (enc_session_t *enc_session_p, uint8_t val)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      enc_session->have_key = val;
  }
  
  
  static const unsigned char *
  lsquic_enc_session_get_enc_key_i (enc_session_t *enc_session_p)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      return enc_session->enc_key_i;
  }
  
  
  static const unsigned char *
  lsquic_enc_session_get_dec_key_i (enc_session_t *enc_session_p)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      return enc_session->dec_key_i;
  }
  
  
  static const unsigned char *
  lsquic_enc_session_get_enc_key_nonce_i (enc_session_t *enc_session_p)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      return enc_session->enc_key_nonce_i;
  }
  
  
  static const unsigned char *
  lsquic_enc_session_get_dec_key_nonce_i (enc_session_t *enc_session_p)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      return enc_session->dec_key_nonce_i;
  }
  
  
  static const unsigned char *
  lsquic_enc_session_get_enc_key_nonce_f (enc_session_t *enc_session_p)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      return enc_session->enc_key_nonce_f;
  }
  
  
  static const unsigned char *
  lsquic_enc_session_get_dec_key_nonce_f (enc_session_t *enc_session_p)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      return enc_session->dec_key_nonce_f;
  }
  
  
  #endif  /* not defined NDEBUG */
  
  
  static size_t
  lsquic_enc_session_mem_used (enc_session_t *enc_session_p)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      size_t size;
  
      size = sizeof(*enc_session);
  
      size += lsquic_str_len(&enc_session->chlo);
      size += lsquic_str_len(&enc_session->sstk);
      size += lsquic_str_len(&enc_session->ssno);
  
      size += lsquic_str_len(&enc_session->hs_ctx.ccs);
      size += lsquic_str_len(&enc_session->hs_ctx.uaid);
      size += lsquic_str_len(&enc_session->hs_ctx.sni);
      size += lsquic_str_len(&enc_session->hs_ctx.ccrt);
      size += lsquic_str_len(&enc_session->hs_ctx.stk);
      size += lsquic_str_len(&enc_session->hs_ctx.sno);
      size += lsquic_str_len(&enc_session->hs_ctx.prof);
      size += lsquic_str_len(&enc_session->hs_ctx.csct);
      if (enc_session->hs_ctx.ccert)
          size += enc_session->hs_ctx.ccert->len
               + sizeof(*enc_session->hs_ctx.ccert);
  
      if (enc_session->info)
      {
          size += sizeof(*enc_session->info);
          size += lsquic_str_len(&enc_session->info->sstk);
          size += lsquic_str_len(&enc_session->info->scfg);
          size += lsquic_str_len(&enc_session->info->sni_key);
      }
  
      /* TODO: calculate memory taken up by SSL stuff */
  
      return size;
  }
  
  
  static int
  lsquic_enc_session_verify_reset_token (enc_session_t *enc_session_p,
                                          const unsigned char *buf, size_t bufsz)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      if (bufsz == SRST_LENGTH
              && 0 == (enc_session->es_flags & ES_SERVER)
              && (enc_session->hs_ctx.set & HSET_SRST)
              && 0 == memcmp(buf, enc_session->hs_ctx.srst, SRST_LENGTH))
          return 0;
      else
          return -1;
  }
  
  
  static int
  lsquic_enc_session_did_sess_resume_succeed (enc_session_t *enc_session_p)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      return !(enc_session->es_flags & ES_RECV_REJ);
  }
  
  
  static int
  lsquic_enc_session_is_sess_resume_enabled (enc_session_t *enc_session_p)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      return enc_session->info && enc_session->cert_item;
  }
  
  
  static ssize_t
  gquic_really_encrypt_packet (struct lsquic_enc_session *enc_session,
      const struct lsquic_conn *lconn, struct lsquic_packet_out *packet_out,
      unsigned char *buf, size_t bufsz)
  {
      int header_sz, is_hello_packet;
      enum enc_level enc_level;
      size_t packet_sz;
      unsigned char header_buf[GQUIC_MAX_PUBHDR_SZ];
  
      header_sz = lconn->cn_pf->pf_gen_reg_pkt_header(lconn, packet_out,
                                  header_buf, sizeof(header_buf), NULL, NULL);
      if (header_sz < 0)
          return -1;
  
      is_hello_packet = !!(packet_out->po_flags & PO_HELLO);
      enc_level = gquic_encrypt_buf(enc_session, lconn->cn_version, 0,
                  packet_out->po_packno, header_buf, header_sz,
                  packet_out->po_data, packet_out->po_data_sz,
                  buf, bufsz, &packet_sz, is_hello_packet);
      if ((int) enc_level >= 0)
      {
          LSQ_DEBUG("encrypted packet %"PRIu64"; plaintext is %zu bytes, "
              "ciphertext is %zd bytes",
              packet_out->po_packno,
              lconn->cn_pf->pf_packout_size(lconn, packet_out) +
                                                  packet_out->po_data_sz,
              packet_sz);
          lsquic_packet_out_set_enc_level(packet_out, enc_level);
          return packet_sz;
      }
      else
          return -1;
  }
  
  
  static STACK_OF(X509) *
  lsquic_enc_session_get_server_cert_chain (enc_session_t *enc_session_p)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      const struct c_cert_item_st *item;
      STACK_OF(X509) *chain;
      X509 *cert;
      int i;
  
      if (enc_session->es_flags & ES_SERVER)
          return NULL;
      item = enc_session->cert_item;
      if (!item)
      {
          LSQ_WARN("could not find certificates for `%.*s'",
                              (int) lsquic_str_len(&enc_session->hs_ctx.sni),
                              lsquic_str_cstr(&enc_session->hs_ctx.sni));
          return NULL;
      }
  
      chain = sk_X509_new_null();
      for (i = 0; i < item->count; ++i)
      {
          cert = lsquic_bio_to_crt(lsquic_str_cstr(&item->crts[i]),
                                  lsquic_str_len(&item->crts[i]), 0);
          if (cert)
              sk_X509_push(chain, cert);
          else
          {
              sk_X509_free(chain);
              return NULL;
          }
      }
  
      return chain;
  }
  
  
  static void
  maybe_dispatch_sess_resume (enc_session_t *enc_session_p,
                  void (*cb)(struct lsquic_conn *, const unsigned char *, size_t))
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      struct lsquic_conn *const lconn = enc_session->es_conn;
      void *buf;
      size_t sz;
      int i;
  
      if (!(enc_session->info && enc_session->cert_item && cb))
      {
          LSQ_DEBUG("no session resumption information or callback is not set");
          return;
      }
  
      for (sz = 0, i = 0; i < enc_session->cert_item->count; ++i)
      {
          sz += sizeof(uint32_t);
          sz += lsquic_str_len(&enc_session->cert_item->crts[i]);
      }
      sz += sizeof(struct lsquic_sess_resume_storage);
  
      buf = malloc(sz);
      if (!buf)
      {
          LSQ_WARN("malloc failed: cannot allocate %zu bytes for session "
                                                              "resumption", sz);
          return;
      }
  
      lsquic_enc_session_serialize_sess_resume(
          (struct lsquic_sess_resume_storage *) buf, lconn->cn_version,
          enc_session->info, enc_session->cert_item);
  
      cb(lconn, buf, sz);
      free(buf);
  }
  
  
  static enum enc_packout
  gquic_encrypt_packet (enc_session_t *enc_session_p,
          const struct lsquic_engine_public *enpub,
          struct lsquic_conn *lconn, struct lsquic_packet_out *packet_out)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      ssize_t enc_sz;
      size_t bufsz;
      unsigned char *buf;
      int ipv6;
  
      assert(!enc_session || lconn == enc_session->es_conn);
  
      bufsz = lconn->cn_pf->pf_packout_size(lconn, packet_out);
      if (bufsz > USHRT_MAX)
          return ENCPA_BADCRYPT;  /* To cause connection to close */
      ipv6 = NP_IS_IPv6(packet_out->po_path);
      buf = enpub->enp_pmi->pmi_allocate(enpub->enp_pmi_ctx,
                          packet_out->po_path->np_peer_ctx, lconn->cn_conn_ctx,
                          bufsz, ipv6);
      if (!buf)
      {
          LSQ_DEBUG("could not allocate memory for outgoing packet of size %zd",
                                                                          bufsz);
          return ENCPA_NOMEM;
      }
  
      enc_sz = gquic_really_encrypt_packet(enc_session,
                                              lconn, packet_out, buf, bufsz);
      if (enc_sz < 0)
      {
          enpub->enp_pmi->pmi_return(enpub->enp_pmi_ctx,
                                  packet_out->po_path->np_peer_ctx, buf, ipv6);
          return ENCPA_BADCRYPT;
      }
  
      packet_out->po_enc_data    = buf;
      packet_out->po_enc_data_sz = enc_sz;
      packet_out->po_sent_sz     = enc_sz;
      packet_out->po_flags &= ~PO_IPv6;
      packet_out->po_flags |= PO_ENCRYPTED|PO_SENT_SZ|(ipv6 << POIPv6_SHIFT);
      packet_out->po_dcid_len = GQUIC_CID_LEN;
  
      return ENCPA_OK;
  }
  
  
  static void
  gquic_esf_set_conn (enc_session_t *enc_session_p, struct lsquic_conn *lconn)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      enc_session->es_conn = lconn;
      LSQ_DEBUG("updated conn reference");
  }
  
  
  #ifdef NDEBUG
  const
  #endif
  struct enc_session_funcs_common lsquic_enc_session_common_gquic_1 =
  {
      .esf_global_init    = lsquic_handshake_init,
      .esf_global_cleanup = lsquic_handshake_cleanup,
      .esf_cipher = lsquic_enc_session_cipher,
      .esf_keysize = lsquic_enc_session_keysize,
      .esf_alg_keysize = lsquic_enc_session_alg_keysize,
      .esf_get_sni = lsquic_enc_session_get_sni,
      .esf_encrypt_packet = gquic_encrypt_packet,
      .esf_decrypt_packet = gquic_decrypt_packet,
      .esf_tag_len = GQUIC_PACKET_HASH_SZ,
      .esf_get_server_cert_chain = lsquic_enc_session_get_server_cert_chain,
      .esf_verify_reset_token = lsquic_enc_session_verify_reset_token,
      .esf_did_sess_resume_succeed = lsquic_enc_session_did_sess_resume_succeed,
      .esf_is_sess_resume_enabled = lsquic_enc_session_is_sess_resume_enabled,
      .esf_set_conn        = gquic_esf_set_conn,
  };
  
  
  static void
  gquic2_gen_hp_mask (struct lsquic_enc_session *enc_session,
          const unsigned char hp[IQUIC_HP_LEN],
          const unsigned char *sample, unsigned char mask[EVP_MAX_BLOCK_LENGTH])
  {
      const EVP_CIPHER *const cipher = EVP_aes_128_ecb();
      EVP_CIPHER_CTX hp_ctx;
      int out_len;
  
      EVP_CIPHER_CTX_init(&hp_ctx);
      if (EVP_EncryptInit_ex(&hp_ctx, cipher, NULL, hp, 0)
          && EVP_EncryptUpdate(&hp_ctx, mask, &out_len, sample, 16))
      {
          assert(out_len >= 5);
      }
      else
      {
          LSQ_WARN("cannot generate hp mask, error code: %"PRIu32,
                                                              ERR_get_error());
          enc_session->es_conn->cn_if->ci_internal_error(enc_session->es_conn,
              "cannot generate hp mask, error code: %"PRIu32, ERR_get_error());
      }
  
      (void) EVP_CIPHER_CTX_cleanup(&hp_ctx);
  
      if (0)
      {
          char hp_str[IQUIC_HP_LEN * 2 + 1], sample_str[16 * 2 + 1];
          LSQ_DEBUG("generated hp mask using hp %s and sample %s",
              HEXSTR(hp, IQUIC_HP_LEN, hp_str),
              HEXSTR(sample, 16, sample_str));
      }
  }
  
  
  static void
  gquic2_apply_hp (struct lsquic_enc_session *enc_session,
          enum gel gel, unsigned char *dst, unsigned packno_off,
          unsigned sample_off, unsigned packno_len)
  {
      unsigned char mask[EVP_MAX_BLOCK_LENGTH];
      char mask_str[5 * 2 + 1];
  
      gquic2_gen_hp_mask(enc_session, enc_session->es_hps[gel][0],
                                                  dst + sample_off, mask);
      LSQ_DEBUG("apply header protection using mask %s",
                                                  HEXSTR(mask, 5, mask_str));
      dst[0] ^= (0xF | (((dst[0] & 0x80) == 0) << 4)) & mask[0];
      switch (packno_len)
      {
      case 4:
          dst[packno_off + 3] ^= mask[4];
          /* fall-through */
      case 3:
          dst[packno_off + 2] ^= mask[3];
          /* fall-through */
      case 2:
          dst[packno_off + 1] ^= mask[2];
          /* fall-through */
      default:
          dst[packno_off + 0] ^= mask[1];
      }
  }
  
  
  static const enum gel hety2gel[] =
  {
      [HETY_NOT_SET]   = GEL_FORW,
      [HETY_VERNEG]    = 0,
      [HETY_INITIAL]   = GEL_CLEAR,
      [HETY_RETRY]     = 0,
      [HETY_HANDSHAKE] = GEL_CLEAR,
      [HETY_0RTT]      = GEL_EARLY,
  };
  
  
  static const char *const gel2str[] =
  {
      [GEL_CLEAR] = "clear",
      [GEL_EARLY] = "early",
      [GEL_FORW]  = "forw-secure",
  };
  
  
  static const enum enc_level gel2el[] =
  {
      [GEL_CLEAR] = ENC_LEV_CLEAR,
      [GEL_EARLY] = ENC_LEV_EARLY,
      [GEL_FORW]  = ENC_LEV_FORW,
  };
  
  
  static enum enc_packout
  gquic2_esf_encrypt_packet (enc_session_t *enc_session_p,
      const struct lsquic_engine_public *enpub, struct lsquic_conn *lconn_UNUSED,
      struct lsquic_packet_out *packet_out)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      struct lsquic_conn *const lconn = enc_session->es_conn;
      EVP_AEAD_CTX *aead_ctx;
      unsigned char *dst;
      enum gel gel;
      unsigned char nonce_buf[ IQUIC_IV_LEN + 8 ];
      unsigned char *nonce, *begin_xor;
      lsquic_packno_t packno;
      size_t out_sz, dst_sz;
      int header_sz;
      int ipv6;
      unsigned packno_off, packno_len, sample_off, divers_nonce_len;
      char errbuf[ERR_ERROR_STRING_BUF_LEN];
  
      gel = hety2gel[ packet_out->po_header_type ];
      aead_ctx = enc_session->es_aead_ctxs[gel][0];
      if (UNLIKELY(!aead_ctx))
      {
          LSQ_WARN("encrypt crypto context at level %s not initialized",
                                                              gel2str[gel]);
          return ENCPA_BADCRYPT;
      }
  
      if (packet_out->po_data_sz < 3)
      {
          /* [draft-ietf-quic-tls-20] Section 5.4.2 */
          enum packno_bits bits = lsquic_packet_out_packno_bits(packet_out);
          /* XXX same packet rules as in IETF QUIC? */
          unsigned len = iquic_packno_bits2len(bits);
          if (packet_out->po_data_sz + len < 4)
          {
              len = 4 - packet_out->po_data_sz - len;
              memset(packet_out->po_data + packet_out->po_data_sz, 0, len);
              packet_out->po_data_sz += len;
              packet_out->po_frame_types |= QUIC_FTBIT_PADDING;
              LSQ_DEBUG("padded packet %"PRIu64" with %u bytes of PADDING",
                  packet_out->po_packno, len);
          }
      }
  
      dst_sz = lconn->cn_pf->pf_packout_size(lconn, packet_out);
      ipv6 = NP_IS_IPv6(packet_out->po_path);
      dst = enpub->enp_pmi->pmi_allocate(enpub->enp_pmi_ctx,
                          packet_out->po_path->np_peer_ctx, lconn->cn_conn_ctx,
                          dst_sz, ipv6);
      if (!dst)
      {
          LSQ_DEBUG("could not allocate memory for outgoing packet of size %zd",
                                                                          dst_sz);
          return ENCPA_NOMEM;
      }
  
      /* Align nonce so we can perform XOR safely in one shot: */
      begin_xor = nonce_buf + sizeof(nonce_buf) - 8;
      begin_xor = (unsigned char *) ((uintptr_t) begin_xor & ~0x7);
      nonce = begin_xor - IQUIC_IV_LEN + 8;
      memcpy(nonce, enc_session->es_ivs[gel][0], IQUIC_IV_LEN);
      packno = packet_out->po_packno;
  #if __BYTE_ORDER == __LITTLE_ENDIAN
      packno = bswap_64(packno);
  #endif
      *((uint64_t *) begin_xor) ^= packno;
  
      header_sz = lconn->cn_pf->pf_gen_reg_pkt_header(lconn, packet_out, dst,
                                              dst_sz, &packno_off, &packno_len);
      if (header_sz < 0)
          goto err;
  
      if (s_log_seal_and_open)
      {
          LSQ_DEBUG("seal: iv (%u bytes): %s", IQUIC_IV_LEN,
              HEXSTR(nonce, IQUIC_IV_LEN, s_str));
          LSQ_DEBUG("seal: ad (%u bytes): %s", header_sz,
              HEXSTR(dst, header_sz, s_str));
          LSQ_DEBUG("seal: in (%hu bytes): %s", packet_out->po_data_sz,
              HEXSTR(packet_out->po_data, packet_out->po_data_sz, s_str));
      }
  
      if (!EVP_AEAD_CTX_seal(aead_ctx, dst + header_sz, &out_sz,
                  dst_sz - header_sz, nonce, IQUIC_IV_LEN,
                  packet_out->po_data, packet_out->po_data_sz, dst, header_sz))
      {
          LSQ_WARN("cannot seal packet #%"PRIu64": %s", packet_out->po_packno,
              ERR_error_string(ERR_get_error(), errbuf));
          goto err;
      }
      assert(out_sz == dst_sz - header_sz);
  
      if (!packet_out->po_nonce)
          divers_nonce_len = 0;
      else
      {
          assert(enc_session->es_flags & ES_SERVER);
          assert(gel == GEL_EARLY);
          divers_nonce_len = DNONC_LENGTH;
      }
      sample_off = packno_off + divers_nonce_len + 4;
      assert(sample_off + IQUIC_TAG_LEN <= dst_sz);
      gquic2_apply_hp(enc_session, gel, dst, packno_off, sample_off, packno_len);
  
      packet_out->po_enc_data    = dst;
      packet_out->po_enc_data_sz = dst_sz;
      packet_out->po_sent_sz     = dst_sz;
      packet_out->po_flags &= ~PO_IPv6;
      packet_out->po_flags |= PO_ENCRYPTED|PO_SENT_SZ|(ipv6 << POIPv6_SHIFT);
      lsquic_packet_out_set_enc_level(packet_out, gel2el[gel]);
      return ENCPA_OK;
  
    err:
      enpub->enp_pmi->pmi_return(enpub->enp_pmi_ctx,
                                  packet_out->po_path->np_peer_ctx, dst, ipv6);
      return ENCPA_BADCRYPT;
  }
  
  
  /* XXX this is an exact copy, can reuse */
  static lsquic_packno_t
  decode_packno (lsquic_packno_t max_packno, lsquic_packno_t packno,
                                                                  unsigned shift)
  {
      lsquic_packno_t candidates[3], epoch_delta;
      int64_t diffs[3];
      unsigned min;;
  
      epoch_delta = 1ULL << shift;
      candidates[1] = (max_packno & ~(epoch_delta - 1)) + packno;
      candidates[0] = candidates[1] - epoch_delta;
      candidates[2] = candidates[1] + epoch_delta;
  
      diffs[0] = llabs((int64_t) candidates[0] - (int64_t) max_packno);
      diffs[1] = llabs((int64_t) candidates[1] - (int64_t) max_packno);
      diffs[2] = llabs((int64_t) candidates[2] - (int64_t) max_packno);
  
      min = diffs[1] < diffs[0];
      if (diffs[2] < diffs[min])
          min = 2;
  
      return candidates[min];
  }
  
  
  static lsquic_packno_t
  gquic2_strip_hp (struct lsquic_enc_session *enc_session,
          enum gel gel, const unsigned char *iv, unsigned char *dst,
          unsigned packno_off, unsigned *packno_len)
  {
      lsquic_packno_t packno;
      unsigned shift;
      unsigned char mask[EVP_MAX_BLOCK_LENGTH];
      char mask_str[5 * 2 + 1];
  
      gquic2_gen_hp_mask(enc_session, enc_session->es_hps[gel][1], iv, mask);
      LSQ_DEBUG("strip header protection using mask %s",
                                                  HEXSTR(mask, 5, mask_str));
      dst[0] ^= (0xF | (((dst[0] & 0x80) == 0) << 4)) & mask[0];
      packno = 0;
      shift = 0;
      *packno_len = 1 + (dst[0] & 3);
      switch (*packno_len)
      {
      case 4:
          dst[packno_off + 3] ^= mask[4];
          packno |= dst[packno_off + 3];
          shift += 8;
          /* fall-through */
      case 3:
          dst[packno_off + 2] ^= mask[3];
          packno |= (unsigned) dst[packno_off + 2] << shift;
          shift += 8;
          /* fall-through */
      case 2:
          dst[packno_off + 1] ^= mask[2];
          packno |= (unsigned) dst[packno_off + 1] << shift;
          shift += 8;
          /* fall-through */
      default:
          dst[packno_off + 0] ^= mask[1];
          packno |= (unsigned) dst[packno_off + 0] << shift;
          shift += 8;
      }
      return decode_packno(enc_session->es_max_packno, packno, shift);
  }
  
  
  static enum dec_packin
  gquic2_esf_decrypt_packet (enc_session_t *enc_session_p,
          struct lsquic_engine_public *enpub, const struct lsquic_conn *lconn,
          struct lsquic_packet_in *packet_in)
  {
      struct lsquic_enc_session *const enc_session = enc_session_p;
      unsigned char *dst;
      unsigned char nonce_buf[ IQUIC_IV_LEN + 8 ];
      unsigned char *nonce, *begin_xor;
      unsigned sample_off, packno_len, divers_nonce_len;
      enum gel gel;
      lsquic_packno_t packno;
      size_t out_sz;
      enum dec_packin dec_packin;
      const size_t dst_sz = packet_in->pi_data_sz;
      char errbuf[ERR_ERROR_STRING_BUF_LEN];
  
      dst = lsquic_mm_get_packet_in_buf(&enpub->enp_mm, dst_sz);
      if (!dst)
      {
          LSQ_WARN("cannot allocate memory to copy incoming packet data");
          dec_packin = DECPI_NOMEM;
          goto err;
      }
  
      if (!(HETY_0RTT == packet_in->pi_header_type
                                  && !(enc_session->es_flags & ES_SERVER)))
          divers_nonce_len = 0;
      else
          divers_nonce_len = DNONC_LENGTH;
  
      gel = hety2gel[packet_in->pi_header_type];
      if (UNLIKELY(!enc_session->es_aead_ctxs[gel][1]))
      {
          LSQ_INFO("decrypt crypto context at level %s not initialized",
                                                              gel2str[gel]);
          dec_packin = DECPI_BADCRYPT;
          goto err;
      }
  
      /* Decrypt packet number.  After this operation, packet_in is adjusted:
       * the packet number becomes part of the header.
       */
      sample_off = packet_in->pi_header_sz + divers_nonce_len + 4;
      if (sample_off + IQUIC_TAG_LEN > packet_in->pi_data_sz)
      {
          LSQ_INFO("packet data is too short: %hu bytes",
                                                  packet_in->pi_data_sz);
          dec_packin = DECPI_TOO_SHORT;
          goto err;
      }
      memcpy(dst, packet_in->pi_data, sample_off);
      packet_in->pi_packno =
      packno = gquic2_strip_hp(enc_session, gel,
          packet_in->pi_data + sample_off,
          dst, packet_in->pi_header_sz, &packno_len);
  
      packet_in->pi_header_sz += packno_len;
      if (UNLIKELY(divers_nonce_len))
      {
          if (enc_session->have_key == 1)
          {
              determine_diversification_key(enc_session,
                                                  dst + packet_in->pi_header_sz);
              enc_session->have_key = 2;
          }
          packet_in->pi_header_sz += divers_nonce_len;
      }
  
      /* Align nonce so we can perform XOR safely in one shot: */
      begin_xor = nonce_buf + sizeof(nonce_buf) - 8;
      begin_xor = (unsigned char *) ((uintptr_t) begin_xor & ~0x7);
      nonce = begin_xor - IQUIC_IV_LEN + 8;
      memcpy(nonce, enc_session->es_ivs[gel][1], IQUIC_IV_LEN);
  #if __BYTE_ORDER == __LITTLE_ENDIAN
      packno = bswap_64(packno);
  #endif
      *((uint64_t *) begin_xor) ^= packno;
  
      if (s_log_seal_and_open)
      {
          LSQ_DEBUG("open: iv (%u bytes): %s", IQUIC_IV_LEN,
              HEXSTR(nonce, IQUIC_IV_LEN, s_str));
          LSQ_DEBUG("open: ad (%u bytes): %s", packet_in->pi_header_sz,
              HEXSTR(dst, packet_in->pi_header_sz, s_str));
          LSQ_DEBUG("open: in (%u bytes): %s",
              packet_in->pi_data_sz - packet_in->pi_header_sz,
              HEXSTR(packet_in->pi_data + packet_in->pi_header_sz,
                     packet_in->pi_data_sz - packet_in->pi_header_sz, s_str));
      }
  
      if (!EVP_AEAD_CTX_open(enc_session->es_aead_ctxs[gel][1],
                  dst + packet_in->pi_header_sz, &out_sz,
                  dst_sz - packet_in->pi_header_sz, nonce, IQUIC_IV_LEN,
                  packet_in->pi_data + packet_in->pi_header_sz,
                  packet_in->pi_data_sz - packet_in->pi_header_sz,
                  dst, packet_in->pi_header_sz))
      {
          LSQ_INFO("cannot open packet #%"PRIu64": %s", packet_in->pi_packno,
              ERR_error_string(ERR_get_error(), errbuf));
          dec_packin = DECPI_BADCRYPT;
          goto err;
      }
  
      /* Bits 2 and 3 are not set and don't need to be checked in gQUIC */
  
      packet_in->pi_data_sz = packet_in->pi_header_sz + out_sz;
      if (packet_in->pi_flags & PI_OWN_DATA)
          lsquic_mm_put_packet_in_buf(&enpub->enp_mm, packet_in->pi_data,
                                                          packet_in->pi_data_sz);
      packet_in->pi_data = dst;
      packet_in->pi_flags |= PI_OWN_DATA | PI_DECRYPTED
                          | (gel2el[gel] << PIBIT_ENC_LEV_SHIFT);
      EV_LOG_CONN_EVENT(LSQUIC_LOG_CONN_ID, "decrypted packet %"PRIu64,
                                                      packet_in->pi_packno);
      if (packet_in->pi_packno > enc_session->es_max_packno)
          enc_session->es_max_packno = packet_in->pi_packno;
      return DECPI_OK;
  
    err:
      if (dst)
          lsquic_mm_put_packet_in_buf(&enpub->enp_mm, dst, dst_sz);
      EV_LOG_CONN_EVENT(LSQUIC_LOG_CONN_ID, "could not decrypt packet (type %s, "
          "number %"PRIu64")", lsquic_hety2str[packet_in->pi_header_type],
                                                      packet_in->pi_packno);
      return dec_packin;
  }
  
  
  #ifdef NDEBUG
  const
  #endif
  /* Q050 and later */
  struct enc_session_funcs_common lsquic_enc_session_common_gquic_2 =
  {
      .esf_get_sni                =  lsquic_enc_session_get_sni,
      .esf_global_init            =  lsquic_handshake_init,
      .esf_global_cleanup         =  lsquic_handshake_cleanup,
      .esf_cipher                 =  lsquic_enc_session_cipher,
      .esf_keysize                =  lsquic_enc_session_keysize,
      .esf_alg_keysize            =  lsquic_enc_session_alg_keysize,
      .esf_get_server_cert_chain  =  lsquic_enc_session_get_server_cert_chain,
      .esf_verify_reset_token     =  lsquic_enc_session_verify_reset_token,
      .esf_did_sess_resume_succeed   =  lsquic_enc_session_did_sess_resume_succeed,
      .esf_is_sess_resume_enabled    =  lsquic_enc_session_is_sess_resume_enabled,
      .esf_set_conn               =  gquic_esf_set_conn,
      /* These are different from gquic_1: */
      .esf_encrypt_packet         =  gquic2_esf_encrypt_packet,
      .esf_decrypt_packet         =  gquic2_esf_decrypt_packet,
      .esf_tag_len                =  IQUIC_TAG_LEN,
  };
  
  
  #ifdef NDEBUG
  const
  #endif
  struct enc_session_funcs_gquic lsquic_enc_session_gquic_gquic_1 =
  {
  #if LSQUIC_KEEP_ENC_SESS_HISTORY
      .esf_get_hist       = lsquic_get_enc_hist,
  #endif
      .esf_destroy = lsquic_enc_session_destroy,
      .esf_is_hsk_done = lsquic_enc_session_is_hsk_done,
      .esf_get_peer_setting = lsquic_enc_session_get_peer_setting,
      .esf_get_peer_option = lsquic_enc_session_get_peer_option,
      .esf_create_server = lsquic_enc_session_create_server,
      .esf_handle_chlo = lsquic_enc_session_handle_chlo,
      .esf_get_ua = lsquic_enc_session_get_ua,
      .esf_have_key_gt_one = lsquic_enc_session_have_key_gt_one,
  #ifndef NDEBUG
      .esf_determine_diversification_key = determine_diversification_key,
      .esf_have_key = lsquic_enc_session_have_key,
      .esf_set_have_key = lsquic_enc_session_set_have_key,
      .esf_get_enc_key_i = lsquic_enc_session_get_enc_key_i,
      .esf_get_dec_key_i = lsquic_enc_session_get_dec_key_i,
      .esf_get_enc_key_nonce_i = lsquic_enc_session_get_enc_key_nonce_i,
      .esf_get_dec_key_nonce_i = lsquic_enc_session_get_dec_key_nonce_i,
      .esf_get_enc_key_nonce_f = lsquic_enc_session_get_enc_key_nonce_f,
      .esf_get_dec_key_nonce_f = lsquic_enc_session_get_dec_key_nonce_f,
  #endif /* !defined(NDEBUG) */
      .esf_create_client = lsquic_enc_session_create_client,
      .esf_gen_chlo = lsquic_enc_session_gen_chlo,
      .esf_handle_chlo_reply = lsquic_enc_session_handle_chlo_reply,
      .esf_mem_used = lsquic_enc_session_mem_used,
      .esf_maybe_dispatch_sess_resume = maybe_dispatch_sess_resume,
      .esf_reset_cid = lsquic_enc_session_reset_cid,
  };
  
  
  typedef char reset_token_lengths_match[
                                  SRST_LENGTH == IQUIC_SRESET_TOKEN_SZ ? 1 : -1];
  
                                  
  