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EVP_MD-SHAKE, EVP_MD-CSHAKE, EVP_MD-CSHAKE-KECCAK,

The SHAKE / KECCAK family EVP_MD implementations

Support for computing SHAKE, CSHAKE or CSHAKE-KECCAK digests through the EVP_MD API.

CSHAKE is an Extendable Output Function (XOF), that allows custom strings "n" and "s". If these strings are both empty then it is identical to SHAKE, otherwise it uses CSHAKE-KECCAK.

CSHAKE-KECCAK is an Extendable Output Function (XOF), with a definition similar to SHAKE but appends 2 extra zero bits. It is used internally by CSHAKE.

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

Known names are "SHAKE-128" and "SHAKE128".
Known names are "SHAKE-256" and "SHAKE256".
Known names are "CSHAKE-128" and "CSHAKE128".
Known names are "CSHAKE-256" and "CSHAKE256".
Other 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).
Other 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).

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.

The CSHAKE-128 and CSHAKE-256 implementations have default digest lengths of 32 and 64 bytes respectively (which correspond to security strengths of 128 and 256 bits respectively).

For SHAKE 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. If it is not set CSHAKE will use the default value. It is recommended to either use EVP_DigestSqueeze() or EVP_DigestFinalXOF() instead.

"size" (OSSL_DIGEST_PARAM_SIZE) <unsigned integer>
An alias of "xoflen".
"function-name" (OSSL_DIGEST_PARAM_FUNCTION_NAME)<UTF8 string>
Sets the function name string used by CSHAKE that can be set to one of "", "TupleHash", "ParallelHash" or "KMAC". The default value is "".
"customization" (OSSL_DIGEST_PARAM_CUSTOMIZATION)<UTF8 string>
Sets a customisation string used by CSHAKE. It is an optional value with a length of at most 512 bytes, and is empty by default.
"properties" (OSSL_DIGEST_PARAM_PROPERTIES) <UTF8 string>
An optional property used internally by CSHAKE when fetching either SHAKE or KECCAK algorithms.

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

For SHAKE-128 and CSHAKE-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 and CSHAKE-256, to ensure the maximum security strength of 256 bits, the output length passed to EVP_DigestFinalXOF() should be at least 64.

The SHA3 specification allows bit strings to be used, but OpenSSL only allows byte strings for inputs, and outputs.

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

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

CSHAKE-128 and CSHAKE-256 were added in OpenSSL 4.0

Copyright 2020-2026 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>.