- NAME
- DESCRIPTION
  - Identities
  - Gettable Parameters
  - Settable Context Parameters
- NOTES
- SEE ALSO
- COPYRIGHT

# 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".

## Gettable Parameters

This implementation supports the common gettable parameters described in EVP_MD-common(7).

## Settable Context Parameters

These implementations support the following OSSL_PARAM(3) entries, settable for an EVP_MD_CTX with EVP_MD_CTX_set_params(3):

"xoflen" (OSSL_DIGEST_PARAM_XOFLEN) <unsigned integer>

  Sets the digest length for extendable output functions. The length of the "xoflen" parameter should not exceed that of a size_t.

  For backwards compatibility reasons the default xoflen length for SHAKE-128 is 16 (bytes) which results in a security strength of only 64 bits. To ensure the maximum security strength of 128 bits, the xoflen should be set to at least 32.

  For backwards compatibility reasons the default xoflen length for SHAKE-256 is 32 (bytes) which results in a security strength of only 128 bits. To ensure the maximum security strength of 256 bits, the xoflen should be set to at least 64.

  This parameter may be used when 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.

# 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)

# COPYRIGHT

Copyright 2020-2023 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.