Cryptography and SSL/TLS Toolkit





Support for computing KMAC MACs through the EVP_MAC API.


These implementations are identified with one of these names and properties, to be used with EVP_MAC_fetch():

"KMAC-128", "provider=default" or "provider=fips"
"KMAC-256", "provider=default" or "provider=fips"

Supported parameters

The general description of these parameters can be found in "PARAMETERS" in EVP_MAC(3).

All these parameters can be set with EVP_MAC_CTX_set_params(). Furthermore, the "size" parameter can be retrieved with EVP_MAC_CTX_get_params(), or with EVP_MAC_CTX_get_mac_size(). The length of the "size" parameter should not exceed that of a size_t.

"key" (OSSL_MAC_PARAM_KEY) <octet string>

Sets the MAC key. Setting this parameter is identical to passing a key to EVP_MAC_init(3).

"custom" (OSSL_MAC_PARAM_CUSTOM) <octet string>

Sets the custom value. It is an optional value of at most 256 bytes, and is empty by default.

"size" (OSSL_MAC_PARAM_SIZE) <unsigned integer>

Sets the MAC size. By default, it is 16 for KMAC-128 and 32 for KMAC-256.

"xof" (OSSL_MAC_PARAM_XOF) <integer>

The "xof" parameter value is expected to be 1 or 0. Use 1 to enable XOF mode. The default value is 0.

The "custom" parameter must be set as part of or before the EVP_MAC_init() call. The "xof" and "size" parameters can be set at any time before EVP_MAC_final(). The "key" parameter is set as part of the EVP_MAC_init() call, but can be set before it instead.


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

  static int do_kmac(const unsigned char *in, size_t in_len,
                     const unsigned char *key, size_t key_len,
                     const unsigned char *custom, size_t custom_len,
                     int xof_enabled, unsigned char *out, int out_len)
      EVP_MAC_CTX *ctx = NULL;
      EVP_MAC *mac = NULL;
      OSSL_PARAM params[4], *p;
      int ret = 0;
      size_t l = 0;

      mac = EVP_MAC_fetch(NULL, "KMAC-128", NULL);
      if (mac == NULL)
          goto err;
      ctx = EVP_MAC_CTX_new(mac);
      /* The mac can be freed after it is used by EVP_MAC_CTX_new */
      if (ctx == NULL)
          goto err;

       * Setup parameters required before calling EVP_MAC_init()
       * The parameters OSSL_MAC_PARAM_XOF and OSSL_MAC_PARAM_SIZE may also be
       * used at this point.
      p = params;
      *p++ = OSSL_PARAM_construct_octet_string(OSSL_MAC_PARAM_KEY,
                                               (void *)key, key_len);
      if (custom != NULL && custom_len != 0)
        *p++ = OSSL_PARAM_construct_octet_string(OSSL_MAC_PARAM_CUSTOM,
                                                 (void *)custom, custom_len);
      *p = OSSL_PARAM_construct_end();
      if (!EVP_MAC_CTX_set_params(ctx, params))
          goto err;

      if (!EVP_MAC_init(ctx))
          goto err;

       * Note: the following optional parameters can be set any time
       * before EVP_MAC_final().
      p = params;
      *p++ = OSSL_PARAM_construct_int(OSSL_MAC_PARAM_XOF, &xof_enabled);
      *p++ = OSSL_PARAM_construct_int(OSSL_MAC_PARAM_SIZE, &out_len);
      *p = OSSL_PARAM_construct_end();
      if (!EVP_MAC_CTX_set_params(ctx, params))
          goto err;

      /* The update may be called multiple times here for streamed input */
      if (!EVP_MAC_update(ctx, in, in_len))
          goto err;
      if (!EVP_MAC_final(ctx, out, &l, out_len))
          goto err;
      ret = 1;
      return ret;


EVP_MAC_CTX_get_params(3), EVP_MAC_CTX_set_params(3), "PARAMETERS" in EVP_MAC(3), OSSL_PARAM(3)

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