text: /*
   *  DTLS cookie callbacks implementation
   *
   *  Copyright The Mbed TLS Contributors
   *  SPDX-License-Identifier: Apache-2.0
   *
   *  Licensed under the Apache License, Version 2.0 (the "License"); you may
   *  not use this file except in compliance with the License.
   *  You may obtain a copy of the License at
   *
   *  http://www.apache.org/licenses/LICENSE-2.0
   *
   *  Unless required by applicable law or agreed to in writing, software
   *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   *  See the License for the specific language governing permissions and
   *  limitations under the License.
   */
  /*
   * These session callbacks use a simple chained list
   * to store and retrieve the session information.
   */
  
  #include "common.h"
  
  #if defined(MBEDTLS_SSL_COOKIE_C)
  
  #if defined(MBEDTLS_PLATFORM_C)
  #include "mbedtls/platform.h"
  #else
  #define mbedtls_calloc    calloc
  #define mbedtls_free      free
  #endif
  
  #include "mbedtls/ssl_cookie.h"
  #include "ssl_misc.h"
  #include "mbedtls/error.h"
  #include "mbedtls/platform_util.h"
  #include "mbedtls/constant_time.h"
  
  #include <string.h>
  
  /*
   * If DTLS is in use, then at least one of SHA-1, SHA-256, SHA-512 is
   * available. Try SHA-256 first, 512 wastes resources
   */
  #if defined(MBEDTLS_SHA224_C)
  #define COOKIE_MD           MBEDTLS_MD_SHA224
  #define COOKIE_MD_OUTLEN    32
  #define COOKIE_HMAC_LEN     28
  #elif defined(MBEDTLS_SHA384_C)
  #define COOKIE_MD           MBEDTLS_MD_SHA384
  #define COOKIE_MD_OUTLEN    48
  #define COOKIE_HMAC_LEN     28
  #elif defined(MBEDTLS_SHA1_C)
  #define COOKIE_MD           MBEDTLS_MD_SHA1
  #define COOKIE_MD_OUTLEN    20
  #define COOKIE_HMAC_LEN     20
  #else
  #error "DTLS hello verify needs SHA-1 or SHA-2"
  #endif
  
  /*
   * Cookies are formed of a 4-bytes timestamp (or serial number) and
   * an HMAC of timestemp and client ID.
   */
  #define COOKIE_LEN      ( 4 + COOKIE_HMAC_LEN )
  
  void mbedtls_ssl_cookie_init( mbedtls_ssl_cookie_ctx *ctx )
  {
      mbedtls_md_init( &ctx->hmac_ctx );
  #if !defined(MBEDTLS_HAVE_TIME)
      ctx->serial = 0;
  #endif
      ctx->timeout = MBEDTLS_SSL_COOKIE_TIMEOUT;
  
  #if defined(MBEDTLS_THREADING_C)
      mbedtls_mutex_init( &ctx->mutex );
  #endif
  }
  
  void mbedtls_ssl_cookie_set_timeout( mbedtls_ssl_cookie_ctx *ctx, unsigned long delay )
  {
      ctx->timeout = delay;
  }
  
  void mbedtls_ssl_cookie_free( mbedtls_ssl_cookie_ctx *ctx )
  {
      mbedtls_md_free( &ctx->hmac_ctx );
  
  #if defined(MBEDTLS_THREADING_C)
      mbedtls_mutex_free( &ctx->mutex );
  #endif
  
      mbedtls_platform_zeroize( ctx, sizeof( mbedtls_ssl_cookie_ctx ) );
  }
  
  int mbedtls_ssl_cookie_setup( mbedtls_ssl_cookie_ctx *ctx,
                        int (*f_rng)(void *, unsigned char *, size_t),
                        void *p_rng )
  {
      int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
      unsigned char key[COOKIE_MD_OUTLEN];
  
      if( ( ret = f_rng( p_rng, key, sizeof( key ) ) ) != 0 )
          return( ret );
  
      ret = mbedtls_md_setup( &ctx->hmac_ctx, mbedtls_md_info_from_type( COOKIE_MD ), 1 );
      if( ret != 0 )
          return( ret );
  
      ret = mbedtls_md_hmac_starts( &ctx->hmac_ctx, key, sizeof( key ) );
      if( ret != 0 )
          return( ret );
  
      mbedtls_platform_zeroize( key, sizeof( key ) );
  
      return( 0 );
  }
  
  /*
   * Generate the HMAC part of a cookie
   */
  static int ssl_cookie_hmac( mbedtls_md_context_t *hmac_ctx,
                              const unsigned char time[4],
                              unsigned char **p, unsigned char *end,
                              const unsigned char *cli_id, size_t cli_id_len )
  {
      unsigned char hmac_out[COOKIE_MD_OUTLEN];
  
      MBEDTLS_SSL_CHK_BUF_PTR( *p, end, COOKIE_HMAC_LEN );
  
      if( mbedtls_md_hmac_reset(  hmac_ctx ) != 0 ||
          mbedtls_md_hmac_update( hmac_ctx, time, 4 ) != 0 ||
          mbedtls_md_hmac_update( hmac_ctx, cli_id, cli_id_len ) != 0 ||
          mbedtls_md_hmac_finish( hmac_ctx, hmac_out ) != 0 )
      {
          return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
      }
  
      memcpy( *p, hmac_out, COOKIE_HMAC_LEN );
      *p += COOKIE_HMAC_LEN;
  
      return( 0 );
  }
  
  /*
   * Generate cookie for DTLS ClientHello verification
   */
  int mbedtls_ssl_cookie_write( void *p_ctx,
                        unsigned char **p, unsigned char *end,
                        const unsigned char *cli_id, size_t cli_id_len )
  {
      int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
      mbedtls_ssl_cookie_ctx *ctx = (mbedtls_ssl_cookie_ctx *) p_ctx;
      unsigned long t;
  
      if( ctx == NULL || cli_id == NULL )
          return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
  
      MBEDTLS_SSL_CHK_BUF_PTR( *p, end, COOKIE_LEN );
  
  #if defined(MBEDTLS_HAVE_TIME)
      t = (unsigned long) mbedtls_time( NULL );
  #else
      t = ctx->serial++;
  #endif
  
      MBEDTLS_PUT_UINT32_BE(t, *p, 0);
      *p += 4;
  
  #if defined(MBEDTLS_THREADING_C)
      if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
          return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_SSL_INTERNAL_ERROR, ret ) );
  #endif
  
      ret = ssl_cookie_hmac( &ctx->hmac_ctx, *p - 4,
                             p, end, cli_id, cli_id_len );
  
  #if defined(MBEDTLS_THREADING_C)
      if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
          return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_SSL_INTERNAL_ERROR,
                  MBEDTLS_ERR_THREADING_MUTEX_ERROR ) );
  #endif
  
      return( ret );
  }
  
  /*
   * Check a cookie
   */
  int mbedtls_ssl_cookie_check( void *p_ctx,
                        const unsigned char *cookie, size_t cookie_len,
                        const unsigned char *cli_id, size_t cli_id_len )
  {
      unsigned char ref_hmac[COOKIE_HMAC_LEN];
      int ret = 0;
      unsigned char *p = ref_hmac;
      mbedtls_ssl_cookie_ctx *ctx = (mbedtls_ssl_cookie_ctx *) p_ctx;
      unsigned long cur_time, cookie_time;
  
      if( ctx == NULL || cli_id == NULL )
          return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
  
      if( cookie_len != COOKIE_LEN )
          return( -1 );
  
  #if defined(MBEDTLS_THREADING_C)
      if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
          return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_SSL_INTERNAL_ERROR, ret ) );
  #endif
  
      if( ssl_cookie_hmac( &ctx->hmac_ctx, cookie,
                           &p, p + sizeof( ref_hmac ),
                           cli_id, cli_id_len ) != 0 )
          ret = -1;
  
  #if defined(MBEDTLS_THREADING_C)
      if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
      {
          ret = MBEDTLS_ERROR_ADD( MBEDTLS_ERR_SSL_INTERNAL_ERROR,
                                   MBEDTLS_ERR_THREADING_MUTEX_ERROR );
      }
  #endif
  
      if( ret != 0 )
          goto exit;
  
      if( mbedtls_ct_memcmp( cookie + 4, ref_hmac, sizeof( ref_hmac ) ) != 0 )
      {
          ret = -1;
          goto exit;
      }
  
  #if defined(MBEDTLS_HAVE_TIME)
      cur_time = (unsigned long) mbedtls_time( NULL );
  #else
      cur_time = ctx->serial;
  #endif
  
      cookie_time = ( (unsigned long) cookie[0] << 24 ) |
                    ( (unsigned long) cookie[1] << 16 ) |
                    ( (unsigned long) cookie[2] <<  8 ) |
                    ( (unsigned long) cookie[3]       );
  
      if( ctx->timeout != 0 && cur_time - cookie_time > ctx->timeout )
      {
          ret = -1;
          goto exit;
      }
  
  exit:
      mbedtls_platform_zeroize( ref_hmac, sizeof( ref_hmac ) );
      return( ret );
  }
  #endif /* MBEDTLS_SSL_COOKIE_C */
  