third_party/libuweave/src/crypto_hmac.c

// Copyright 2015 The Weave Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "src/crypto_hmac.h"

#include <stddef.h>
#include <stdint.h>
#include <string.h>

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

bool uw_crypto_hmac_(const uint8_t* key,
                     size_t key_len,
                     const UwCryptoHmacMsg messages[],
                     size_t num_messages,
                     uint8_t* truncated_digest,
                     size_t truncated_digest_len) {
  HMAC_CTX context = {0};
  HMAC_CTX_init(&context);
  if (!HMAC_Init(&context, key, key_len, EVP_sha256()))
    return false;

  for (size_t i = 0; i < num_messages; ++i) {
    if (messages[i].num_bytes &&
        (!messages[i].bytes ||
         !HMAC_Update(&context, messages[i].bytes, messages[i].num_bytes))) {
      return false;
    }
  }

  const size_t kFullDigestLen = (size_t)EVP_MD_size(EVP_sha256());
  if (truncated_digest_len > kFullDigestLen) {
    return false;
  }

  uint8_t digest[kFullDigestLen];
  uint32_t len = kFullDigestLen;

  bool result = HMAC_Final(&context, digest, &len) && kFullDigestLen == len;
  HMAC_CTX_cleanup(&context);
  if (result) {
    memcpy(truncated_digest, digest, truncated_digest_len);
  }
  return result;
}