EVP_MD-SHAKE(7)

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>.

2026-04-07 | 3.5.6