crypto/fipsmodule/hkdf/hkdf.cc.inc

// Copyright 2014 The BoringSSL Authors
//
// 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
//
//     https://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.

#include <openssl/hkdf.h>

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

#include <openssl/err.h>
#include <openssl/hmac.h>

#include "../../internal.h"


int HKDF(uint8_t *out_key, size_t out_len, const EVP_MD *digest,
         const uint8_t *secret, size_t secret_len, const uint8_t *salt,
         size_t salt_len, const uint8_t *info, size_t info_len) {
  // https://tools.ietf.org/html/rfc5869#section-2
  uint8_t prk[EVP_MAX_MD_SIZE];
  size_t prk_len;

  if (!HKDF_extract(prk, &prk_len, digest, secret, secret_len, salt,
                    salt_len) ||
      !HKDF_expand(out_key, out_len, digest, prk, prk_len, info, info_len)) {
    return 0;
  }

  return 1;
}

int HKDF_extract(uint8_t *out_key, size_t *out_len, const EVP_MD *digest,
                 const uint8_t *secret, size_t secret_len, const uint8_t *salt,
                 size_t salt_len) {
  // https://tools.ietf.org/html/rfc5869#section-2.2

  // If salt is not given, HashLength zeros are used. However, HMAC does that
  // internally already so we can ignore it.
  unsigned len;
  if (HMAC(digest, salt, salt_len, secret, secret_len, out_key, &len) == NULL) {
    OPENSSL_PUT_ERROR(HKDF, ERR_R_HMAC_LIB);
    return 0;
  }
  *out_len = len;
  assert(*out_len == EVP_MD_size(digest));
  return 1;
}

int HKDF_expand(uint8_t *out_key, size_t out_len, const EVP_MD *digest,
                const uint8_t *prk, size_t prk_len, const uint8_t *info,
                size_t info_len) {
  // https://tools.ietf.org/html/rfc5869#section-2.3
  const size_t digest_len = EVP_MD_size(digest);
  uint8_t previous[EVP_MAX_MD_SIZE];
  size_t n, done = 0;
  unsigned i;
  int ret = 0;
  HMAC_CTX hmac;

  // Expand key material to desired length.
  n = (out_len + digest_len - 1) / digest_len;
  if (out_len + digest_len < out_len || n > 255) {
    OPENSSL_PUT_ERROR(HKDF, HKDF_R_OUTPUT_TOO_LARGE);
    return 0;
  }

  HMAC_CTX_init(&hmac);
  if (!HMAC_Init_ex(&hmac, prk, prk_len, digest, NULL)) {
    goto out;
  }

  for (i = 0; i < n; i++) {
    uint8_t ctr = i + 1;
    size_t todo;

    if (i != 0 && (!HMAC_Init_ex(&hmac, NULL, 0, NULL, NULL) ||
                   !HMAC_Update(&hmac, previous, digest_len))) {
      goto out;
    }
    if (!HMAC_Update(&hmac, info, info_len) ||
        !HMAC_Update(&hmac, &ctr, 1) ||
        !HMAC_Final(&hmac, previous, NULL)) {
      goto out;
    }

    todo = digest_len;
    if (todo > out_len - done) {
      todo = out_len - done;
    }
    OPENSSL_memcpy(out_key + done, previous, todo);
    done += todo;
  }

  ret = 1;

out:
  HMAC_CTX_cleanup(&hmac);
  if (ret != 1) {
    OPENSSL_PUT_ERROR(HKDF, ERR_R_HMAC_LIB);
  }
  return ret;
}