# man > EVP_MAC-KMAC(7)

[_EVP_MAC-KMAC_(7SSL)](https://www.chedong.com/phpMan.php/man/EVPMAC-KMAC/7SSL/markdown)                             OpenSSL                            [_EVP_MAC-KMAC_(7SSL)](https://www.chedong.com/phpMan.php/man/EVPMAC-KMAC/7SSL/markdown)

## NAME
       EVP_MAC-KMAC, EVP_MAC-KMAC128, EVP_MAC-KMAC256 - The KMAC EVP_MAC implementations

## DESCRIPTION
       Support for computing KMAC MACs through the **EVP_MAC **API.

### Identity
       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)](https://www.chedong.com/phpMan.php/man/EVPMAC/3/markdown).

       All  these  parameters  (except  for  "block-size") 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**.  Likewise, the "block-size" parameter can be retrieved with **EVP_MAC_CTX_get_params()**,
       or with **EVP_MAC_CTX_get_block_size()**.

       "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)](https://www.chedong.com/phpMan.php/man/EVPMACinit/3/markdown).  The length of the key (in bytes) must be in the range 4...512.

       "custom" (**OSSL_MAC_PARAM_CUSTOM**) <octet string>
           Sets  the  customization  string.   It  is an optional value with a length of at most 512
           bytes, and is empty by default.

       "size" (**OSSL_MAC_PARAM_SIZE**) <unsigned integer>
           Sets the MAC size.  By default, it is 32 for "KMAC-128" and 64 for "KMAC-256".

       "block-size" (**OSSL_MAC_PARAM_BLOCK_SIZE**) <unsigned integer>
           Gets the MAC block size.  It is 168 for "KMAC-128" and 136 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.

## EXAMPLES
         #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 */
             EVP_MAC_free(mac);
             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;
         err:
             EVP_MAC_CTX_free(ctx);
             return ret;
         }

## SEE ALSO
       [**EVP_MAC_CTX_get_params**(3)](https://www.chedong.com/phpMan.php/man/EVPMACCTXgetparams/3/markdown),    [**EVP_MAC_CTX_set_params**(3)](https://www.chedong.com/phpMan.php/man/EVPMACCTXsetparams/3/markdown),    "PARAMETERS"    in    [**EVP_MAC**(3)](https://www.chedong.com/phpMan.php/man/EVPMAC/3/markdown),
       [**OSSL_PARAM**(3)](https://www.chedong.com/phpMan.php/man/OSSLPARAM/3/markdown)

## COPYRIGHT
       Copyright 2018-2021 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (the "License").  You may not use this file  except  in
       compliance  with  the  License.   You  can  obtain  a  copy in the file LICENSE in the source
       distribution or at <<https://www.openssl.org/source/license.html>>.

3.0.13                                       2026-07-29                           [_EVP_MAC-KMAC_(7SSL)](https://www.chedong.com/phpMan.php/man/EVPMAC-KMAC/7SSL/markdown)