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.\"
.IX Title "EVP_MD-SHAKE 7ossl"
.TH EVP_MD-SHAKE 7ossl "2026-01-27" "3.5.5" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH "NAME"
EVP_MD\-SHAKE, EVP_MD\-KECCAK\-KMAC
\&\- The SHAKE / KECCAK family EVP_MD implementations
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Support for computing \s-1SHAKE\s0 or KECCAK-KMAC digests through the
\&\fB\s-1EVP_MD\s0\fR \s-1API.\s0
.PP
KECCAK-KMAC is an Extendable Output Function (\s-1XOF\s0), with a definition
similar to \s-1SHAKE,\s0 used by the \s-1KMAC EVP_MAC\s0 implementation (see
\&\s-1\fBEVP_MAC\-KMAC\s0\fR\|(7)).
.SS "Identities"
.IX Subsection "Identities"
This implementation is available in the \s-1FIPS\s0 provider as well as the default
provider, and includes the following varieties:
.IP "\s-1KECCAK\-KMAC\-128\s0" 4
.IX Item "KECCAK-KMAC-128"
Known names are \*(L"\s-1KECCAK\-KMAC\-128\*(R"\s0 and \*(L"\s-1KECCAK\-KMAC128\*(R".\s0  This is used
by \s-1\fBEVP_MAC\-KMAC128\s0\fR\|(7).  Using the notation from \s-1NIST FIPS 202\s0
(Section 6.2), we have \s-1KECCAK\-KMAC\-128\s0(M,\ d) = KECCAK[256](M\ ||\ 00,\ d)
(see the description of \s-1KMAC128\s0 in Appendix A of \s-1NIST SP 800\-185\s0).
.IP "\s-1KECCAK\-KMAC\-256\s0" 4
.IX Item "KECCAK-KMAC-256"
Known names are \*(L"\s-1KECCAK\-KMAC\-256\*(R"\s0 and \*(L"\s-1KECCAK\-KMAC256\*(R".\s0  This is used
by \s-1\fBEVP_MAC\-KMAC256\s0\fR\|(7).  Using the notation from \s-1NIST FIPS 202\s0
(Section 6.2), we have \s-1KECCAK\-KMAC\-256\s0(M,\ d) = KECCAK[512](M\ ||\ 00,\ d)
(see the description of \s-1KMAC256\s0 in Appendix A of \s-1NIST SP 800\-185\s0).
.IP "\s-1SHAKE\-128\s0" 4
.IX Item "SHAKE-128"
Known names are \*(L"\s-1SHAKE\-128\*(R"\s0 and \*(L"\s-1SHAKE128\*(R".\s0
.IP "\s-1SHAKE\-256\s0" 4
.IX Item "SHAKE-256"
Known names are \*(L"\s-1SHAKE\-256\*(R"\s0 and \*(L"\s-1SHAKE256\*(R".\s0
.SS "Parameters"
.IX Subsection "Parameters"
This implementation supports the following \s-1\fBOSSL_PARAM\s0\fR\|(3) entries:
.ie n .IP """xoflen"" (\fB\s-1OSSL_DIGEST_PARAM_XOFLEN\s0\fR) <unsigned integer>" 4
.el .IP "``xoflen'' (\fB\s-1OSSL_DIGEST_PARAM_XOFLEN\s0\fR) <unsigned integer>" 4
.IX Item "xoflen (OSSL_DIGEST_PARAM_XOFLEN) <unsigned integer>"
Sets or Gets the digest length for extendable output functions.
The length of the \*(L"xoflen\*(R" parameter should not exceed that of a \fBsize_t\fR.
.Sp
The \s-1SHAKE\-128\s0 and \s-1SHAKE\-256\s0 implementations do not have any default digest
length.
.Sp
This parameter must be set before calling either \fBEVP_DigestFinal_ex()\fR or
\&\fBEVP_DigestFinal()\fR, since these functions were not designed to handle variable
length output. It is recommended to either use \fBEVP_DigestSqueeze()\fR or
\&\fBEVP_DigestFinalXOF()\fR instead.
.ie n .IP """size"" (\fB\s-1OSSL_DIGEST_PARAM_SIZE\s0\fR) <unsigned integer>" 4
.el .IP "``size'' (\fB\s-1OSSL_DIGEST_PARAM_SIZE\s0\fR) <unsigned integer>" 4
.IX Item "size (OSSL_DIGEST_PARAM_SIZE) <unsigned integer>"
An alias of \*(L"xoflen\*(R".
.PP
See \*(L"\s-1PARAMETERS\*(R"\s0 in \fBEVP_DigestInit\fR\|(3) for further information related to parameters
.SH "NOTES"
.IX Header "NOTES"
For \s-1SHAKE\-128,\s0 to ensure the maximum security strength of 128 bits, the output
length passed to \fBEVP_DigestFinalXOF()\fR should be at least 32.
.PP
For \s-1SHAKE\-256,\s0 to ensure the maximum security strength of 256 bits, the output
length passed to \fBEVP_DigestFinalXOF()\fR should be at least 64.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBEVP_MD_CTX_set_params\fR\|(3), \fBprovider\-digest\fR\|(7), \fBOSSL_PROVIDER\-default\fR\|(7)
.SH "HISTORY"
.IX Header "HISTORY"
Since OpenSSL 3.4 the \s-1SHAKE\-128\s0 and \s-1SHAKE\-256\s0 implementations have no default
digest length.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2020\-2024 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the Apache License 2.0 (the \*(L"License\*(R").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.
