text: /* This Source Code Form is subject to the terms of the Mozilla Public
   * License, v. 2.0. If a copy of the MPL was not distributed with this
   * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
  
  /*
   * Diffie-Hellman parameter generation, key generation, and secret derivation.
   * KEA secret generation and verification.
   */
  #ifdef FREEBL_NO_DEPEND
  #include "stubs.h"
  #endif
  
  #include "prerr.h"
  #include "secerr.h"
  
  #include "blapi.h"
  #include "secitem.h"
  #include "mpi.h"
  #include "mpprime.h"
  #include "secmpi.h"
  
  #define KEA_DERIVED_SECRET_LEN 128
  
  /* Lengths are in bytes. */
  static unsigned int
  dh_GetSecretKeyLen(unsigned int primeLen)
  {
      /* Based on Table 2 in NIST SP 800-57. */
      if (primeLen >= 1920) { /* 15360 bits */
          return 64;  /* 512 bits */
      }
      if (primeLen >= 960) { /* 7680 bits */
          return 48;  /* 384 bits */
      }
      if (primeLen >= 384) { /* 3072 bits */
          return 32;  /* 256 bits */
      }
      if (primeLen >= 256) { /* 2048 bits */
          return 28;  /* 224 bits */
      }
      return 20;  /* 160 bits */
  }
  
  SECStatus 
  DH_GenParam(int primeLen, DHParams **params)
  {
      PLArenaPool *arena;
      DHParams *dhparams;
      unsigned char *pb = NULL;
      unsigned char *ab = NULL;
      unsigned long counter = 0;
      mp_int p, q, a, h, psub1, test;
      mp_err err = MP_OKAY;
      SECStatus rv = SECSuccess;
      if (!params || primeLen < 0) {
  	PORT_SetError(SEC_ERROR_INVALID_ARGS);
  	return SECFailure;
      }
      arena = PORT_NewArena(NSS_FREEBL_DEFAULT_CHUNKSIZE);
      if (!arena) {
  	PORT_SetError(SEC_ERROR_NO_MEMORY);
  	return SECFailure;
      }
      dhparams = (DHParams *)PORT_ArenaZAlloc(arena, sizeof(DHParams));
      if (!dhparams) {
  	PORT_SetError(SEC_ERROR_NO_MEMORY);
  	PORT_FreeArena(arena, PR_TRUE);
  	return SECFailure;
      }
      dhparams->arena = arena;
      MP_DIGITS(&p) = 0;
      MP_DIGITS(&q) = 0;
      MP_DIGITS(&a) = 0;
      MP_DIGITS(&h) = 0;
      MP_DIGITS(&psub1) = 0;
      MP_DIGITS(&test) = 0;
      CHECK_MPI_OK( mp_init(&p) );
      CHECK_MPI_OK( mp_init(&q) );
      CHECK_MPI_OK( mp_init(&a) );
      CHECK_MPI_OK( mp_init(&h) );
      CHECK_MPI_OK( mp_init(&psub1) );
      CHECK_MPI_OK( mp_init(&test) );
      /* generate prime with MPI, uses Miller-Rabin to generate strong prime. */
      pb = PORT_Alloc(primeLen);
      CHECK_SEC_OK( RNG_GenerateGlobalRandomBytes(pb, primeLen) );
      pb[0]          |= 0x80; /* set high-order bit */
      pb[primeLen-1] |= 0x01; /* set low-order bit  */
      CHECK_MPI_OK( mp_read_unsigned_octets(&p, pb, primeLen) );
      CHECK_MPI_OK( mpp_make_prime(&p, primeLen * 8, PR_TRUE, &counter) );
      /* construct Sophie-Germain prime q = (p-1)/2. */
      CHECK_MPI_OK( mp_sub_d(&p, 1, &psub1) );
      CHECK_MPI_OK( mp_div_2(&psub1, &q)    );
      /* construct a generator from the prime. */
      ab = PORT_Alloc(primeLen);
      /* generate a candidate number a in p's field */
      CHECK_SEC_OK( RNG_GenerateGlobalRandomBytes(ab, primeLen) );
      CHECK_MPI_OK( mp_read_unsigned_octets(&a, ab, primeLen) );
      /* force a < p (note that quot(a/p) <= 1) */
      if ( mp_cmp(&a, &p) > 0 )
  	CHECK_MPI_OK( mp_sub(&a, &p, &a) );
      do {
  	/* check that a is in the range [2..p-1] */
  	if ( mp_cmp_d(&a, 2) < 0 || mp_cmp(&a, &psub1) >= 0) {
  	    /* a is outside of the allowed range.  Set a=3 and keep going. */
              mp_set(&a, 3);
  	}
  	/* if a**q mod p != 1 then a is a generator */
  	CHECK_MPI_OK( mp_exptmod(&a, &q, &p, &test) );
  	if ( mp_cmp_d(&test, 1) != 0 )
  	    break;
  	/* increment the candidate and try again. */
  	CHECK_MPI_OK( mp_add_d(&a, 1, &a) );
      } while (PR_TRUE);
      MPINT_TO_SECITEM(&p, &dhparams->prime, arena);
      MPINT_TO_SECITEM(&a, &dhparams->base, arena);
      *params = dhparams;
  cleanup:
      mp_clear(&p);
      mp_clear(&q);
      mp_clear(&a);
      mp_clear(&h);
      mp_clear(&psub1);
      mp_clear(&test);
      if (pb) PORT_ZFree(pb, primeLen);
      if (ab) PORT_ZFree(ab, primeLen);
      if (err) {
  	MP_TO_SEC_ERROR(err);
  	rv = SECFailure;
      }
      if (rv)
  	PORT_FreeArena(arena, PR_TRUE);
      return rv;
  }
  
  SECStatus 
  DH_NewKey(DHParams *params, DHPrivateKey **privKey)
  {
      PLArenaPool *arena;
      DHPrivateKey *key;
      mp_int g, xa, p, Ya;
      mp_err   err = MP_OKAY;
      SECStatus rv = SECSuccess;
      if (!params || !privKey) {
  	PORT_SetError(SEC_ERROR_INVALID_ARGS);
  	return SECFailure;
      }
      arena = PORT_NewArena(NSS_FREEBL_DEFAULT_CHUNKSIZE);
      if (!arena) {
  	PORT_SetError(SEC_ERROR_NO_MEMORY);
  	return SECFailure;
      }
      key = (DHPrivateKey *)PORT_ArenaZAlloc(arena, sizeof(DHPrivateKey));
      if (!key) {
  	PORT_SetError(SEC_ERROR_NO_MEMORY);
  	PORT_FreeArena(arena, PR_TRUE);
  	return SECFailure;
      }
      key->arena = arena;
      MP_DIGITS(&g)  = 0;
      MP_DIGITS(&xa) = 0;
      MP_DIGITS(&p)  = 0;
      MP_DIGITS(&Ya) = 0;
      CHECK_MPI_OK( mp_init(&g)  );
      CHECK_MPI_OK( mp_init(&xa) );
      CHECK_MPI_OK( mp_init(&p)  );
      CHECK_MPI_OK( mp_init(&Ya) );
      /* Set private key's p */
      CHECK_SEC_OK( SECITEM_CopyItem(arena, &key->prime, &params->prime) );
      SECITEM_TO_MPINT(key->prime, &p);
      /* Set private key's g */
      CHECK_SEC_OK( SECITEM_CopyItem(arena, &key->base, &params->base) );
      SECITEM_TO_MPINT(key->base, &g);
      /* Generate private key xa */
      SECITEM_AllocItem(arena, &key->privateValue,
                        dh_GetSecretKeyLen(params->prime.len));
      RNG_GenerateGlobalRandomBytes(key->privateValue.data, 
                                    key->privateValue.len);
      SECITEM_TO_MPINT( key->privateValue, &xa );
      /* xa < p */
      CHECK_MPI_OK( mp_mod(&xa, &p, &xa) );
      /* Compute public key Ya = g ** xa mod p */
      CHECK_MPI_OK( mp_exptmod(&g, &xa, &p, &Ya) );
      MPINT_TO_SECITEM(&Ya, &key->publicValue, key->arena);
      *privKey = key;
  cleanup:
      mp_clear(&g);
      mp_clear(&xa);
      mp_clear(&p);
      mp_clear(&Ya);
      if (err) {
  	MP_TO_SEC_ERROR(err);
  	rv = SECFailure;
      }
      if (rv)
  	PORT_FreeArena(arena, PR_TRUE);
      return rv;
  }
  
  SECStatus 
  DH_Derive(SECItem *publicValue, 
            SECItem *prime, 
            SECItem *privateValue, 
            SECItem *derivedSecret, 
            unsigned int outBytes)
  {
      mp_int p, Xa, Yb, ZZ, psub1;
      mp_err err = MP_OKAY;
      unsigned int len = 0;
      unsigned int nb;
      unsigned char *secret = NULL;
      if (!publicValue || !prime || !privateValue || !derivedSecret) {
  	PORT_SetError(SEC_ERROR_INVALID_ARGS);
  	return SECFailure;
      }
      memset(derivedSecret, 0, sizeof *derivedSecret);
      MP_DIGITS(&p)  = 0;
      MP_DIGITS(&Xa) = 0;
      MP_DIGITS(&Yb) = 0;
      MP_DIGITS(&ZZ) = 0;
      MP_DIGITS(&psub1) = 0;
      CHECK_MPI_OK( mp_init(&p)  );
      CHECK_MPI_OK( mp_init(&Xa) );
      CHECK_MPI_OK( mp_init(&Yb) );
      CHECK_MPI_OK( mp_init(&ZZ) );
      CHECK_MPI_OK( mp_init(&psub1) );
      SECITEM_TO_MPINT(*publicValue,  &Yb);
      SECITEM_TO_MPINT(*privateValue, &Xa);
      SECITEM_TO_MPINT(*prime,        &p);
      CHECK_MPI_OK( mp_sub_d(&p, 1, &psub1) );
  
      /* We assume that the modulus, p, is a safe prime. That is, p = 2q+1 where
       * q is also a prime. Thus the orders of the subgroups are factors of 2q:
       * namely 1, 2, q and 2q.
       *
       * We check that the peer's public value isn't zero (which isn't in the
       * group), one (subgroup of order one) or p-1 (subgroup of order 2). We
       * also check that the public value is less than p, to avoid being fooled
       * by values like p+1 or 2*p-1.
       *
       * Thus we must be operating in the subgroup of size q or 2q. */
      if (mp_cmp_d(&Yb, 1) <= 0 ||
  	mp_cmp(&Yb, &psub1) >= 0) {
  	err = MP_BADARG;
  	goto cleanup;
      }
  
      /* ZZ = (Yb)**Xa mod p */
      CHECK_MPI_OK( mp_exptmod(&Yb, &Xa, &p, &ZZ) );
      /* number of bytes in the derived secret */
      len = mp_unsigned_octet_size(&ZZ);
      if (len <= 0) {
          err = MP_BADARG;
          goto cleanup;
      }
  
      /*
       * We check to make sure that ZZ is not equal to 1 or -1 mod p.
       * This helps guard against small subgroup attacks, since an attacker
       * using a subgroup of size N will produce 1 or -1 with probability 1/N.
       * When the protocol is executed within a properly large subgroup, the
       * probability of this result will be negligibly small.  For example,
       * with a strong prime of the form 2p+1, the probability will be 1/p.
       *
       * We return MP_BADARG because this is probably the result of a bad
       * public value or a bad prime having been provided.
       */
      if (mp_cmp_d(&ZZ, 1) == 0 ||
          mp_cmp(&ZZ, &psub1) == 0) {
          err = MP_BADARG;
          goto cleanup;
      }
  
      /* allocate a buffer which can hold the entire derived secret. */
      secret = PORT_Alloc(len);
      /* grab the derived secret */
      err = mp_to_unsigned_octets(&ZZ, secret, len);
      if (err >= 0) err = MP_OKAY;
      /* 
      ** if outBytes is 0 take all of the bytes from the derived secret.
      ** if outBytes is not 0 take exactly outBytes from the derived secret, zero
      ** pad at the beginning if necessary, and truncate beginning bytes 
      ** if necessary.
      */
      if (outBytes > 0)
  	nb = outBytes;
      else
  	nb = len;
      SECITEM_AllocItem(NULL, derivedSecret, nb);
      if (len < nb) {
  	unsigned int offset = nb - len;
  	memset(derivedSecret->data, 0, offset);
  	memcpy(derivedSecret->data + offset, secret, len);
      } else {
  	memcpy(derivedSecret->data, secret + len - nb, nb);
      }
  cleanup:
      mp_clear(&p);
      mp_clear(&Xa);
      mp_clear(&Yb);
      mp_clear(&ZZ);
      mp_clear(&psub1);
      if (secret) {
  	/* free the buffer allocated for the full secret. */
  	PORT_ZFree(secret, len);
      }
      if (err) {
  	MP_TO_SEC_ERROR(err);
  	if (derivedSecret->data) 
  	    PORT_ZFree(derivedSecret->data, derivedSecret->len);
  	return SECFailure;
      }
      return SECSuccess;
  }
  
  SECStatus 
  KEA_Derive(SECItem *prime, 
             SECItem *public1, 
             SECItem *public2, 
             SECItem *private1, 
             SECItem *private2,
             SECItem *derivedSecret)
  {
      mp_int p, Y, R, r, x, t, u, w;
      mp_err err;
      unsigned char *secret = NULL;
      unsigned int len = 0, offset;
      if (!prime || !public1 || !public2 || !private1 || !private2 ||
          !derivedSecret) {
  	PORT_SetError(SEC_ERROR_INVALID_ARGS);
  	return SECFailure;
      }
      memset(derivedSecret, 0, sizeof *derivedSecret);
      MP_DIGITS(&p) = 0;
      MP_DIGITS(&Y) = 0;
      MP_DIGITS(&R) = 0;
      MP_DIGITS(&r) = 0;
      MP_DIGITS(&x) = 0;
      MP_DIGITS(&t) = 0;
      MP_DIGITS(&u) = 0;
      MP_DIGITS(&w) = 0;
      CHECK_MPI_OK( mp_init(&p) );
      CHECK_MPI_OK( mp_init(&Y) );
      CHECK_MPI_OK( mp_init(&R) );
      CHECK_MPI_OK( mp_init(&r) );
      CHECK_MPI_OK( mp_init(&x) );
      CHECK_MPI_OK( mp_init(&t) );
      CHECK_MPI_OK( mp_init(&u) );
      CHECK_MPI_OK( mp_init(&w) );
      SECITEM_TO_MPINT(*prime,    &p);
      SECITEM_TO_MPINT(*public1,  &Y);
      SECITEM_TO_MPINT(*public2,  &R);
      SECITEM_TO_MPINT(*private1, &r);
      SECITEM_TO_MPINT(*private2, &x);
      /* t = DH(Y, r, p) = Y ** r mod p */
      CHECK_MPI_OK( mp_exptmod(&Y, &r, &p, &t) );
      /* u = DH(R, x, p) = R ** x mod p */
      CHECK_MPI_OK( mp_exptmod(&R, &x, &p, &u) );
      /* w = (t + u) mod p */
      CHECK_MPI_OK( mp_addmod(&t, &u, &p, &w) );
      /* allocate a buffer for the full derived secret */
      len = mp_unsigned_octet_size(&w);
      secret = PORT_Alloc(len);
      /* grab the secret */
      err = mp_to_unsigned_octets(&w, secret, len);
      if (err > 0) err = MP_OKAY;
      /* allocate output buffer */
      SECITEM_AllocItem(NULL, derivedSecret, KEA_DERIVED_SECRET_LEN);
      memset(derivedSecret->data, 0, derivedSecret->len);
      /* copy in the 128 lsb of the secret */
      if (len >= KEA_DERIVED_SECRET_LEN) {
  	memcpy(derivedSecret->data, secret + (len - KEA_DERIVED_SECRET_LEN),
  	       KEA_DERIVED_SECRET_LEN);
      } else {
  	offset = KEA_DERIVED_SECRET_LEN - len;
  	memcpy(derivedSecret->data + offset, secret, len);
      }
  cleanup:
      mp_clear(&p);
      mp_clear(&Y);
      mp_clear(&R);
      mp_clear(&r);
      mp_clear(&x);
      mp_clear(&t);
      mp_clear(&u);
      mp_clear(&w);
      if (secret)
  	PORT_ZFree(secret, len);
      if (err) {
  	MP_TO_SEC_ERROR(err);
  	return SECFailure;
      }
      return SECSuccess;
  }
  
  PRBool 
  KEA_Verify(SECItem *Y, SECItem *prime, SECItem *subPrime)
  {
      mp_int p, q, y, r;
      mp_err err;
      int cmp = 1;  /* default is false */
      if (!Y || !prime || !subPrime) {
  	PORT_SetError(SEC_ERROR_INVALID_ARGS);
  	return SECFailure;
      }
      MP_DIGITS(&p) = 0;
      MP_DIGITS(&q) = 0;
      MP_DIGITS(&y) = 0;
      MP_DIGITS(&r) = 0;
      CHECK_MPI_OK( mp_init(&p) );
      CHECK_MPI_OK( mp_init(&q) );
      CHECK_MPI_OK( mp_init(&y) );
      CHECK_MPI_OK( mp_init(&r) );
      SECITEM_TO_MPINT(*prime,    &p);
      SECITEM_TO_MPINT(*subPrime, &q);
      SECITEM_TO_MPINT(*Y,        &y);
      /* compute r = y**q mod p */
      CHECK_MPI_OK( mp_exptmod(&y, &q, &p, &r) );
      /* compare to 1 */
      cmp = mp_cmp_d(&r, 1);
  cleanup:
      mp_clear(&p);
      mp_clear(&q);
      mp_clear(&y);
      mp_clear(&r);
      if (err) {
  	MP_TO_SEC_ERROR(err);
  	return PR_FALSE;
      }
      return (cmp == 0) ? PR_TRUE : PR_FALSE;
  }
  