ssl/t1_enc.c

/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
 * All rights reserved.
 *
 * This package is an SSL implementation written
 * by Eric Young (eay@cryptsoft.com).
 * The implementation was written so as to conform with Netscapes SSL.
 *
 * This library is free for commercial and non-commercial use as long as
 * the following conditions are aheared to.  The following conditions
 * apply to all code found in this distribution, be it the RC4, RSA,
 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
 * included with this distribution is covered by the same copyright terms
 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
 *
 * Copyright remains Eric Young's, and as such any Copyright notices in
 * the code are not to be removed.
 * If this package is used in a product, Eric Young should be given attribution
 * as the author of the parts of the library used.
 * This can be in the form of a textual message at program startup or
 * in documentation (online or textual) provided with the package.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    "This product includes cryptographic software written by
 *     Eric Young (eay@cryptsoft.com)"
 *    The word 'cryptographic' can be left out if the rouines from the library
 *    being used are not cryptographic related :-).
 * 4. If you include any Windows specific code (or a derivative thereof) from
 *    the apps directory (application code) you must include an acknowledgement:
 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
 *
 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * The licence and distribution terms for any publically available version or
 * derivative of this code cannot be changed.  i.e. this code cannot simply be
 * copied and put under another distribution licence
 * [including the GNU Public Licence.]
 */
/* ====================================================================
 * Copyright (c) 1998-2007 The OpenSSL Project.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. All advertising materials mentioning features or use of this
 *    software must display the following acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
 *
 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission. For written permission, please contact
 *    openssl-core@openssl.org.
 *
 * 5. Products derived from this software may not be called "OpenSSL"
 *    nor may "OpenSSL" appear in their names without prior written
 *    permission of the OpenSSL Project.
 *
 * 6. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
 *
 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 * ====================================================================
 *
 * This product includes cryptographic software written by Eric Young
 * (eay@cryptsoft.com).  This product includes software written by Tim
 * Hudson (tjh@cryptsoft.com).
 *
 */
/* ====================================================================
 * Copyright 2005 Nokia. All rights reserved.
 *
 * The portions of the attached software ("Contribution") is developed by
 * Nokia Corporation and is licensed pursuant to the OpenSSL open source
 * license.
 *
 * The Contribution, originally written by Mika Kousa and Pasi Eronen of
 * Nokia Corporation, consists of the "PSK" (Pre-Shared Key) ciphersuites
 * support (see RFC 4279) to OpenSSL.
 *
 * No patent licenses or other rights except those expressly stated in
 * the OpenSSL open source license shall be deemed granted or received
 * expressly, by implication, estoppel, or otherwise.
 *
 * No assurances are provided by Nokia that the Contribution does not
 * infringe the patent or other intellectual property rights of any third
 * party or that the license provides you with all the necessary rights
 * to make use of the Contribution.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. IN
 * ADDITION TO THE DISCLAIMERS INCLUDED IN THE LICENSE, NOKIA
 * SPECIFICALLY DISCLAIMS ANY LIABILITY FOR CLAIMS BROUGHT BY YOU OR ANY
 * OTHER ENTITY BASED ON INFRINGEMENT OF INTELLECTUAL PROPERTY RIGHTS OR
 * OTHERWISE. */

#include <openssl/ssl.h>

#include <assert.h>
#include <stdio.h>
#include <string.h>

#include <openssl/err.h>
#include <openssl/evp.h>
#include <openssl/hmac.h>
#include <openssl/md5.h>
#include <openssl/mem.h>
#include <openssl/obj.h>
#include <openssl/rand.h>

#include "internal.h"


/* tls1_P_hash computes the TLS P_<hash> function as described in RFC 5246,
 * section 5. It XORs |out_len| bytes to |out|, using |md| as the hash and
 * |secret| as the secret. |seed1| through |seed3| are concatenated to form the
 * seed parameter. It returns one on success and zero on failure. */
static int tls1_P_hash(uint8_t *out, size_t out_len, const EVP_MD *md,
                       const uint8_t *secret, size_t secret_len,
                       const uint8_t *seed1, size_t seed1_len,
                       const uint8_t *seed2, size_t seed2_len,
                       const uint8_t *seed3, size_t seed3_len) {
  size_t chunk;
  HMAC_CTX ctx, ctx_tmp, ctx_init;
  uint8_t A1[EVP_MAX_MD_SIZE];
  unsigned A1_len;
  int ret = 0;

  chunk = EVP_MD_size(md);

  HMAC_CTX_init(&ctx);
  HMAC_CTX_init(&ctx_tmp);
  HMAC_CTX_init(&ctx_init);
  if (!HMAC_Init_ex(&ctx_init, secret, secret_len, md, NULL) ||
      !HMAC_CTX_copy_ex(&ctx, &ctx_init) ||
      (seed1_len && !HMAC_Update(&ctx, seed1, seed1_len)) ||
      (seed2_len && !HMAC_Update(&ctx, seed2, seed2_len)) ||
      (seed3_len && !HMAC_Update(&ctx, seed3, seed3_len)) ||
      !HMAC_Final(&ctx, A1, &A1_len)) {
    goto err;
  }

  for (;;) {
    /* Reinit mac contexts. */
    if (!HMAC_CTX_copy_ex(&ctx, &ctx_init) ||
        !HMAC_Update(&ctx, A1, A1_len) ||
        (out_len > chunk && !HMAC_CTX_copy_ex(&ctx_tmp, &ctx)) ||
        (seed1_len && !HMAC_Update(&ctx, seed1, seed1_len)) ||
        (seed2_len && !HMAC_Update(&ctx, seed2, seed2_len)) ||
        (seed3_len && !HMAC_Update(&ctx, seed3, seed3_len))) {
      goto err;
    }

    unsigned len;
    uint8_t hmac[EVP_MAX_MD_SIZE];
    if (!HMAC_Final(&ctx, hmac, &len)) {
      goto err;
    }
    assert(len == chunk);

    /* XOR the result into |out|. */
    if (len > out_len) {
      len = out_len;
    }
    unsigned i;
    for (i = 0; i < len; i++) {
      out[i] ^= hmac[i];
    }
    out += len;
    out_len -= len;

    if (out_len == 0) {
      break;
    }

    /* Calculate the next A1 value. */
    if (!HMAC_Final(&ctx_tmp, A1, &A1_len)) {
      goto err;
    }
  }

  ret = 1;

err:
  HMAC_CTX_cleanup(&ctx);
  HMAC_CTX_cleanup(&ctx_tmp);
  HMAC_CTX_cleanup(&ctx_init);
  OPENSSL_cleanse(A1, sizeof(A1));
  return ret;
}

int tls1_prf(SSL *s, uint8_t *out, size_t out_len, const uint8_t *secret,
             size_t secret_len, const char *label, size_t label_len,
             const uint8_t *seed1, size_t seed1_len,
             const uint8_t *seed2, size_t seed2_len) {

  if (out_len == 0) {
    return 1;
  }

  memset(out, 0, out_len);

  uint32_t algorithm_prf = ssl_get_algorithm_prf(s);
  if (algorithm_prf == SSL_HANDSHAKE_MAC_DEFAULT) {
    /* If using the MD5/SHA1 PRF, |secret| is partitioned between SHA-1 and
     * MD5, MD5 first. */
    size_t secret_half = secret_len - (secret_len / 2);
    if (!tls1_P_hash(out, out_len, EVP_md5(), secret, secret_half,
                     (const uint8_t *)label, label_len, seed1, seed1_len, seed2,
                     seed2_len)) {
      return 0;
    }

    /* Note that, if |secret_len| is odd, the two halves share a byte. */
    secret = secret + (secret_len - secret_half);
    secret_len = secret_half;
  }

  if (!tls1_P_hash(out, out_len, ssl_get_handshake_digest(algorithm_prf),
                   secret, secret_len, (const uint8_t *)label, label_len,
                   seed1, seed1_len, seed2, seed2_len)) {
    return 0;
  }

  return 1;
}

static int tls1_generate_key_block(SSL *s, uint8_t *out, size_t out_len) {
  return s->enc_method->prf(s, out, out_len, s->session->master_key,
                            s->session->master_key_length,
                            TLS_MD_KEY_EXPANSION_CONST,
                            TLS_MD_KEY_EXPANSION_CONST_SIZE,
                            s->s3->server_random, SSL3_RANDOM_SIZE,
                            s->s3->client_random,
                            SSL3_RANDOM_SIZE);
}

int tls1_change_cipher_state(SSL *s, int which) {
  /* is_read is true if we have just read a ChangeCipherSpec message - i.e. we
   * need to update the read cipherspec. Otherwise we have just written one. */
  const char is_read = (which & SSL3_CC_READ) != 0;
  /* use_client_keys is true if we wish to use the keys for the "client write"
   * direction. This is the case if we're a client sending a ChangeCipherSpec,
   * or a server reading a client's ChangeCipherSpec. */
  const char use_client_keys = which == SSL3_CHANGE_CIPHER_CLIENT_WRITE ||
                               which == SSL3_CHANGE_CIPHER_SERVER_READ;
  const uint8_t *client_write_mac_secret, *server_write_mac_secret, *mac_secret;
  const uint8_t *client_write_key, *server_write_key, *key;
  const uint8_t *client_write_iv, *server_write_iv, *iv;
  const EVP_AEAD *aead = s->s3->tmp.new_aead;
  size_t key_len, iv_len, mac_secret_len;
  const uint8_t *key_data;

  /* Reset sequence number to zero. */
  if (!SSL_IS_DTLS(s)) {
    memset(is_read ? s->s3->read_sequence : s->s3->write_sequence, 0, 8);
  }

  mac_secret_len = s->s3->tmp.new_mac_secret_len;
  iv_len = s->s3->tmp.new_fixed_iv_len;

  if (aead == NULL) {
    OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
    return 0;
  }

  key_len = EVP_AEAD_key_length(aead);
  if (mac_secret_len > 0) {
    /* For "stateful" AEADs (i.e. compatibility with pre-AEAD cipher
     * suites) the key length reported by |EVP_AEAD_key_length| will
     * include the MAC and IV key bytes. */
    if (key_len < mac_secret_len + iv_len) {
      OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
      return 0;
    }
    key_len -= mac_secret_len + iv_len;
  }

  key_data = s->s3->tmp.key_block;
  client_write_mac_secret = key_data;
  key_data += mac_secret_len;
  server_write_mac_secret = key_data;
  key_data += mac_secret_len;
  client_write_key = key_data;
  key_data += key_len;
  server_write_key = key_data;
  key_data += key_len;
  client_write_iv = key_data;
  key_data += iv_len;
  server_write_iv = key_data;
  key_data += iv_len;

  if (use_client_keys) {
    mac_secret = client_write_mac_secret;
    key = client_write_key;
    iv = client_write_iv;
  } else {
    mac_secret = server_write_mac_secret;
    key = server_write_key;
    iv = server_write_iv;
  }

  if (key_data - s->s3->tmp.key_block != s->s3->tmp.key_block_length) {
    OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
    return 0;
  }

  if (is_read) {
    SSL_AEAD_CTX_free(s->aead_read_ctx);
    s->aead_read_ctx = SSL_AEAD_CTX_new(
        evp_aead_open, ssl3_version_from_wire(s, s->version),
        s->s3->tmp.new_cipher, key, key_len, mac_secret, mac_secret_len, iv,
        iv_len);
    return s->aead_read_ctx != NULL;
  }

  SSL_AEAD_CTX_free(s->aead_write_ctx);
  s->aead_write_ctx = SSL_AEAD_CTX_new(
      evp_aead_seal, ssl3_version_from_wire(s, s->version),
      s->s3->tmp.new_cipher, key, key_len, mac_secret, mac_secret_len, iv,
      iv_len);
  if (s->aead_write_ctx == NULL) {
    return 0;
  }

  s->s3->need_record_splitting = 0;
  if (!SSL_USE_EXPLICIT_IV(s) &&
      (s->mode & SSL_MODE_CBC_RECORD_SPLITTING) != 0 &&
      SSL_CIPHER_is_block_cipher(s->s3->tmp.new_cipher)) {
    /* Enable 1/n-1 record-splitting to randomize the IV. See
     * https://www.openssl.org/~bodo/tls-cbc.txt and the BEAST attack. */
    s->s3->need_record_splitting = 1;
  }
  return 1;
}

int tls1_setup_key_block(SSL *s) {
  uint8_t *p;
  const EVP_AEAD *aead = NULL;
  int ret = 0;
  size_t mac_secret_len, fixed_iv_len, variable_iv_len, key_len;
  size_t key_block_len;

  if (s->s3->tmp.key_block_length != 0) {
    return 1;
  }

  if (s->session->cipher == NULL) {
    goto cipher_unavailable_err;
  }

  if (!ssl_cipher_get_evp_aead(&aead, &mac_secret_len, &fixed_iv_len,
                               s->session->cipher,
                               ssl3_version_from_wire(s, s->version))) {
    goto cipher_unavailable_err;
  }
  key_len = EVP_AEAD_key_length(aead);
  variable_iv_len = EVP_AEAD_nonce_length(aead);
  if (mac_secret_len > 0) {
    /* For "stateful" AEADs (i.e. compatibility with pre-AEAD cipher suites) the
     * key length reported by |EVP_AEAD_key_length| will include the MAC key
     * bytes and initial implicit IV. */
    if (key_len < mac_secret_len + fixed_iv_len) {
      OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
      return 0;
    }
    key_len -= mac_secret_len + fixed_iv_len;
  } else {
    /* The nonce is split into a fixed portion and a variable portion. */
    if (variable_iv_len < fixed_iv_len) {
      OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
      return 0;
    }
    variable_iv_len -= fixed_iv_len;
  }

  assert(mac_secret_len < 256);
  assert(fixed_iv_len < 256);
  assert(variable_iv_len < 256);

  s->s3->tmp.new_aead = aead;
  s->s3->tmp.new_mac_secret_len = (uint8_t)mac_secret_len;
  s->s3->tmp.new_fixed_iv_len = (uint8_t)fixed_iv_len;
  s->s3->tmp.new_variable_iv_len = (uint8_t)variable_iv_len;

  key_block_len = key_len + mac_secret_len + fixed_iv_len;
  key_block_len *= 2;

  ssl3_cleanup_key_block(s);

  p = (uint8_t *)OPENSSL_malloc(key_block_len);
  if (p == NULL) {
    OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
    goto err;
  }

  s->s3->tmp.key_block_length = key_block_len;
  s->s3->tmp.key_block = p;

  if (!tls1_generate_key_block(s, p, key_block_len)) {
    goto err;
  }

  ret = 1;

err:
  return ret;

cipher_unavailable_err:
  OPENSSL_PUT_ERROR(SSL, SSL_R_CIPHER_OR_HASH_UNAVAILABLE);
  return 0;
}

int tls1_cert_verify_mac(SSL *s, int md_nid, uint8_t *out) {
  const EVP_MD_CTX *ctx_template;
  if (md_nid == NID_md5) {
    ctx_template = &s->s3->handshake_md5;
  } else if (md_nid == EVP_MD_CTX_type(&s->s3->handshake_hash)) {
    ctx_template = &s->s3->handshake_hash;
  } else {
    OPENSSL_PUT_ERROR(SSL, SSL_R_NO_REQUIRED_DIGEST);
    return 0;
  }

  EVP_MD_CTX ctx;
  EVP_MD_CTX_init(&ctx);
  if (!EVP_MD_CTX_copy_ex(&ctx, ctx_template)) {
    EVP_MD_CTX_cleanup(&ctx);
    return 0;
  }
  unsigned ret;
  EVP_DigestFinal_ex(&ctx, out, &ret);
  EVP_MD_CTX_cleanup(&ctx);
  return ret;
}

static int append_digest(const EVP_MD_CTX *ctx, uint8_t *out, size_t *out_len,
                         size_t max_out) {
  int ret = 0;
  EVP_MD_CTX ctx_copy;
  EVP_MD_CTX_init(&ctx_copy);

  if (EVP_MD_CTX_size(ctx) > max_out) {
    OPENSSL_PUT_ERROR(SSL, SSL_R_BUFFER_TOO_SMALL);
    goto err;
  }
  unsigned len;
  if (!EVP_MD_CTX_copy_ex(&ctx_copy, ctx) ||
      !EVP_DigestFinal_ex(&ctx_copy, out, &len)) {
    goto err;
  }
  assert(len == EVP_MD_CTX_size(ctx));

  *out_len = len;
  ret = 1;

err:
  EVP_MD_CTX_cleanup(&ctx_copy);
  return ret;
}

/* tls1_handshake_digest calculates the current handshake hash and writes it to
 * |out|, which has space for |out_len| bytes. It returns the number of bytes
 * written or -1 in the event of an error. This function works on a copy of the
 * underlying digests so can be called multiple times and prior to the final
 * update etc. */
int tls1_handshake_digest(SSL *s, uint8_t *out, size_t out_len) {
  size_t md5_len = 0;
  if (EVP_MD_CTX_md(&s->s3->handshake_md5) != NULL &&
      !append_digest(&s->s3->handshake_md5, out, &md5_len, out_len)) {
    return -1;
  }

  size_t len;
  if (!append_digest(&s->s3->handshake_hash, out + md5_len, &len,
                     out_len - md5_len)) {
    return -1;
  }

  return (int)(md5_len + len);
}

int tls1_final_finish_mac(SSL *s, const char *str, int slen, uint8_t *out) {
  uint8_t buf[2 * EVP_MAX_MD_SIZE];
  int err = 0;
  int digests_len;

  /* At this point, the handshake should have released the handshake buffer on
   * its own. */
  assert(s->s3->handshake_buffer == NULL);

  digests_len = tls1_handshake_digest(s, buf, sizeof(buf));
  if (digests_len < 0) {
    err = 1;
    digests_len = 0;
  }

  if (!s->enc_method->prf(s, out, 12, s->session->master_key,
                          s->session->master_key_length, str, slen, buf,
                          digests_len, NULL, 0)) {
    err = 1;
  }

  if (err) {
    return 0;
  } else {
    return 12;
  }
}

int tls1_generate_master_secret(SSL *s, uint8_t *out, const uint8_t *premaster,
                                size_t premaster_len) {
  if (s->s3->tmp.extended_master_secret) {
    uint8_t digests[2 * EVP_MAX_MD_SIZE];
    int digests_len = tls1_handshake_digest(s, digests, sizeof(digests));
    if (digests_len == -1) {
      return 0;
    }

    if (!s->enc_method->prf(s, out, SSL3_MASTER_SECRET_SIZE, premaster,
                            premaster_len, TLS_MD_EXTENDED_MASTER_SECRET_CONST,
                            TLS_MD_EXTENDED_MASTER_SECRET_CONST_SIZE, digests,
                            digests_len, NULL, 0)) {
      return 0;
    }
  } else {
    if (!s->enc_method->prf(s, out, SSL3_MASTER_SECRET_SIZE, premaster,
                            premaster_len, TLS_MD_MASTER_SECRET_CONST,
                            TLS_MD_MASTER_SECRET_CONST_SIZE,
                            s->s3->client_random, SSL3_RANDOM_SIZE,
                            s->s3->server_random, SSL3_RANDOM_SIZE)) {
      return 0;
    }
  }

  return SSL3_MASTER_SECRET_SIZE;
}

int tls1_export_keying_material(SSL *s, uint8_t *out, size_t out_len,
                                const char *label, size_t label_len,
                                const uint8_t *context, size_t context_len,
                                int use_context) {
  if (!s->s3->have_version || s->version == SSL3_VERSION) {
    OPENSSL_PUT_ERROR(SSL, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED);
    return 0;
  }

  size_t seed_len = 2 * SSL3_RANDOM_SIZE;
  if (use_context) {
    if (context_len >= 1u << 16) {
      OPENSSL_PUT_ERROR(SSL, ERR_R_OVERFLOW);
      return 0;
    }
    seed_len += 2 + context_len;
  }
  uint8_t *seed = OPENSSL_malloc(seed_len);
  if (seed == NULL) {
    OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
    return 0;
  }

  memcpy(seed, s->s3->client_random, SSL3_RANDOM_SIZE);
  memcpy(seed + SSL3_RANDOM_SIZE, s->s3->server_random, SSL3_RANDOM_SIZE);
  if (use_context) {
    seed[2 * SSL3_RANDOM_SIZE] = (uint8_t)(context_len >> 8);
    seed[2 * SSL3_RANDOM_SIZE + 1] = (uint8_t)context_len;
    memcpy(seed + 2 * SSL3_RANDOM_SIZE + 2, context, context_len);
  }

  int ret = s->enc_method->prf(s, out, out_len, s->session->master_key,
                               s->session->master_key_length, label, label_len,
                               seed, seed_len, NULL, 0);
  OPENSSL_free(seed);
  return ret;
}

int tls1_alert_code(int code) {
  switch (code) {
    case SSL_AD_CLOSE_NOTIFY:
      return SSL3_AD_CLOSE_NOTIFY;

    case SSL_AD_UNEXPECTED_MESSAGE:
      return SSL3_AD_UNEXPECTED_MESSAGE;

    case SSL_AD_BAD_RECORD_MAC:
      return SSL3_AD_BAD_RECORD_MAC;

    case SSL_AD_DECRYPTION_FAILED:
      return TLS1_AD_DECRYPTION_FAILED;

    case SSL_AD_RECORD_OVERFLOW:
      return TLS1_AD_RECORD_OVERFLOW;

    case SSL_AD_DECOMPRESSION_FAILURE:
      return SSL3_AD_DECOMPRESSION_FAILURE;

    case SSL_AD_HANDSHAKE_FAILURE:
      return SSL3_AD_HANDSHAKE_FAILURE;

    case SSL_AD_NO_CERTIFICATE:
      return -1;

    case SSL_AD_BAD_CERTIFICATE:
      return SSL3_AD_BAD_CERTIFICATE;

    case SSL_AD_UNSUPPORTED_CERTIFICATE:
      return SSL3_AD_UNSUPPORTED_CERTIFICATE;

    case SSL_AD_CERTIFICATE_REVOKED:
      return SSL3_AD_CERTIFICATE_REVOKED;

    case SSL_AD_CERTIFICATE_EXPIRED:
      return SSL3_AD_CERTIFICATE_EXPIRED;

    case SSL_AD_CERTIFICATE_UNKNOWN:
      return SSL3_AD_CERTIFICATE_UNKNOWN;

    case SSL_AD_ILLEGAL_PARAMETER:
      return SSL3_AD_ILLEGAL_PARAMETER;

    case SSL_AD_UNKNOWN_CA:
      return TLS1_AD_UNKNOWN_CA;

    case SSL_AD_ACCESS_DENIED:
      return TLS1_AD_ACCESS_DENIED;

    case SSL_AD_DECODE_ERROR:
      return TLS1_AD_DECODE_ERROR;

    case SSL_AD_DECRYPT_ERROR:
      return TLS1_AD_DECRYPT_ERROR;
    case SSL_AD_EXPORT_RESTRICTION:
      return TLS1_AD_EXPORT_RESTRICTION;

    case SSL_AD_PROTOCOL_VERSION:
      return TLS1_AD_PROTOCOL_VERSION;

    case SSL_AD_INSUFFICIENT_SECURITY:
      return TLS1_AD_INSUFFICIENT_SECURITY;

    case SSL_AD_INTERNAL_ERROR:
      return TLS1_AD_INTERNAL_ERROR;

    case SSL_AD_USER_CANCELLED:
      return TLS1_AD_USER_CANCELLED;

    case SSL_AD_NO_RENEGOTIATION:
      return TLS1_AD_NO_RENEGOTIATION;

    case SSL_AD_UNSUPPORTED_EXTENSION:
      return TLS1_AD_UNSUPPORTED_EXTENSION;

    case SSL_AD_CERTIFICATE_UNOBTAINABLE:
      return TLS1_AD_CERTIFICATE_UNOBTAINABLE;

    case SSL_AD_UNRECOGNIZED_NAME:
      return TLS1_AD_UNRECOGNIZED_NAME;

    case SSL_AD_BAD_CERTIFICATE_STATUS_RESPONSE:
      return TLS1_AD_BAD_CERTIFICATE_STATUS_RESPONSE;

    case SSL_AD_BAD_CERTIFICATE_HASH_VALUE:
      return TLS1_AD_BAD_CERTIFICATE_HASH_VALUE;

    case SSL_AD_UNKNOWN_PSK_IDENTITY:
      return TLS1_AD_UNKNOWN_PSK_IDENTITY;

    case SSL_AD_INAPPROPRIATE_FALLBACK:
      return SSL3_AD_INAPPROPRIATE_FALLBACK;

    default:
      return -1;
  }
}