Updated: 2025/Nov/16

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EVP_MD-SHAKE(7)                     OpenSSL                    EVP_MD-SHAKE(7)


NAME
       EVP_MD-SHAKE, EVP_MD-KECCAK-KMAC - The SHAKE / KECCAK family EVP_MD
       implementations

DESCRIPTION
       Support for computing SHAKE or KECCAK-KMAC digests through the EVP_MD
       API.

       KECCAK-KMAC is an Extendable Output Function (XOF), with a definition
       similar to SHAKE, used by the KMAC EVP_MAC implementation (see
       EVP_MAC-KMAC(7)).

   Identities
       This implementation is available in the FIPS provider as well as the
       default provider, and includes the following varieties:

       KECCAK-KMAC-128
           Known names are "KECCAK-KMAC-128" and "KECCAK-KMAC128".  This is
           used by EVP_MAC-KMAC128(7).  Using the notation from NIST FIPS 202
           (Section 6.2), we have KECCAK-KMAC-128(M, d) =
           KECCAK[256](M || 00, d) (see the description of KMAC128 in Appendix
           A of NIST SP 800-185).

       KECCAK-KMAC-256
           Known names are "KECCAK-KMAC-256" and "KECCAK-KMAC256".  This is
           used by EVP_MAC-KMAC256(7).  Using the notation from NIST FIPS 202
           (Section 6.2), we have KECCAK-KMAC-256(M, d) =
           KECCAK[512](M || 00, d) (see the description of KMAC256 in Appendix
           A of NIST SP 800-185).

       SHAKE-128
           Known names are "SHAKE-128" and "SHAKE128".

       SHAKE-256
           Known names are "SHAKE-256" and "SHAKE256".

   Parameters
       This implementation supports the following OSSL_PARAM(3) entries:

       "xoflen" (OSSL_DIGEST_PARAM_XOFLEN) <unsigned integer>
           Sets or Gets the digest length for extendable output functions.
           The length of the "xoflen" parameter should not exceed that of a
           size_t.

           The SHAKE-128 and SHAKE-256 implementations do not have any default
           digest length.

           This parameter must be set before calling either
           EVP_DigestFinal_ex() or EVP_DigestFinal(), since these functions
           were not designed to handle variable length output. It is
           recommended to either use EVP_DigestSqueeze() or
           EVP_DigestFinalXOF() instead.

       "size" (OSSL_DIGEST_PARAM_SIZE) <unsigned integer>
           An alias of "xoflen".

       See "PARAMETERS" in EVP_DigestInit(3) for further information related
       to parameters

NOTES
       For SHAKE-128, to ensure the maximum security strength of 128 bits, the
       output length passed to EVP_DigestFinalXOF() should be at least 32.

       For SHAKE-256, to ensure the maximum security strength of 256 bits, the
       output length passed to EVP_DigestFinalXOF() should be at least 64.

SEE ALSO
       EVP_MD_CTX_set_params(3), provider-digest(7), OSSL_PROVIDER-default(7)

HISTORY
       Since OpenSSL 3.4 the SHAKE-128 and SHAKE-256 implementations have no
       default digest length.

COPYRIGHT
       Copyright 2020-2024 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>.

3.5.1                             2025-07-01                   EVP_MD-SHAKE(7)