Function cupsHMACData

cups/hash.c:129–185

//

ssize_t					// O - The length of the HMAC or `-1` on error
cupsHMACData(
    const char          *algorithm,	// I - Hash algorithm
    const unsigned char *key,		// I - Key
    size_t              keylen,		// I - Length of key
    const void          *data,		// I - Data to hash
    size_t              datalen,	// I - Length of data to hash
    unsigned char       *hmac,		// I - HMAC buffer
    size_t              hmacsize)	// I - Size of HMAC buffer
{
  size_t	i,			// Looping var
		b;			// Block size
  unsigned char	buffer[128],		// Intermediate buffer
		hash[128],		// Hash buffer
		hkey[128];		// Hashed key buffer
  ssize_t	hashlen;		// Length of hash


  // Range check input...
  if (!algorithm || !key || keylen == 0 || !data || datalen == 0 || !hmac || hmacsize < 32)
    return (-1);

  // Determine the block size...
  if (!strcmp(algorithm, "sha2-384") || !strncmp(algorithm, "sha2-512", 8))
    b = 128;
  else
    b = 64;

  // If the key length is larger than the block size, hash it and use that
  // instead...
  if (keylen > b)
  {
    if ((hashlen = hash_data(algorithm, hkey, sizeof(hkey), key, keylen, NULL, 0)) < 0)
      return (-1);

    key    = hkey;
    keylen = (size_t)hashlen;
  }

  // HMAC = H(K' ^ opad, H(K' ^ ipad, data))
  // K'   = Klen > b ? H(K) : K, padded with 0's
  // opad = 0x5c, ipad = 0x36
  for (i = 0; i < b && i < keylen; i ++)
    buffer[i] = key[i] ^ 0x36;
  for (; i < b; i ++)
    buffer[i] = 0x36;

  if ((hashlen = hash_data(algorithm, hash, sizeof(hash), buffer, b, data, datalen)) < 0)
    return (-1);

  for (i = 0; i < b && i < keylen; i ++)
    buffer[i] = key[i] ^ 0x5c;
  for (; i < b; i ++)
    buffer[i] = 0x5c;

  return (hash_data(algorithm, hmac, hmacsize, buffer, b, hash, (size_t)hashlen));
}