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.\"
.IX Title "EVP_MAC-GMAC 7"
.TH EVP_MAC-GMAC 7 "2023-05-07" "3.0.12" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH "NAME"
EVP_MAC\-GMAC \- The GMAC EVP_MAC implementation
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Support for computing \s-1GMAC\s0 MACs through the \fB\s-1EVP_MAC\s0\fR \s-1API.\s0
.PP
This implementation uses \s-1EVP_CIPHER\s0 functions to get access to the underlying
cipher.
.SS "Identity"
.IX Subsection "Identity"
This implementation is identified with this name and properties, to be
used with \fBEVP_MAC_fetch()\fR:
.ie n .IP """\s-1GMAC"",\s0 ""provider=default"" or ""provider=fips""" 4
.el .IP "``\s-1GMAC'',\s0 ``provider=default'' or ``provider=fips''" 4
.IX Item "GMAC, provider=default or provider=fips"
.SS "Supported parameters"
.IX Subsection "Supported parameters"
The general description of these parameters can be found in
\&\*(L"\s-1PARAMETERS\*(R"\s0 in \s-1\fBEVP_MAC\s0\fR\|(3).
.PP
The following parameter can be set with \fBEVP_MAC_CTX_set_params()\fR:
.ie n .IP """key"" (\fB\s-1OSSL_MAC_PARAM_KEY\s0\fR) <octet string>" 4
.el .IP "``key'' (\fB\s-1OSSL_MAC_PARAM_KEY\s0\fR) <octet string>" 4
.IX Item "key (OSSL_MAC_PARAM_KEY) <octet string>"
Sets the \s-1MAC\s0 key.
Setting this parameter is identical to passing a \fIkey\fR to \fBEVP_MAC_init\fR\|(3).
.ie n .IP """iv"" (\fB\s-1OSSL_MAC_PARAM_IV\s0\fR) <octet string>" 4
.el .IP "``iv'' (\fB\s-1OSSL_MAC_PARAM_IV\s0\fR) <octet string>" 4
.IX Item "iv (OSSL_MAC_PARAM_IV) <octet string>"
Sets the \s-1IV\s0 of the underlying cipher, when applicable.
.ie n .IP """cipher"" (\fB\s-1OSSL_MAC_PARAM_CIPHER\s0\fR) <\s-1UTF8\s0 string>" 4
.el .IP "``cipher'' (\fB\s-1OSSL_MAC_PARAM_CIPHER\s0\fR) <\s-1UTF8\s0 string>" 4
.IX Item "cipher (OSSL_MAC_PARAM_CIPHER) <UTF8 string>"
Sets the name of the underlying cipher to be used.
.ie n .IP """properties"" (\fB\s-1OSSL_MAC_PARAM_PROPERTIES\s0\fR) <\s-1UTF8\s0 string>" 4
.el .IP "``properties'' (\fB\s-1OSSL_MAC_PARAM_PROPERTIES\s0\fR) <\s-1UTF8\s0 string>" 4
.IX Item "properties (OSSL_MAC_PARAM_PROPERTIES) <UTF8 string>"
Sets the properties to be queried when trying to fetch the underlying cipher.
This must be given together with the cipher naming parameter to be considered
valid.
.PP
The following parameters can be retrieved with
\&\fBEVP_MAC_CTX_get_params()\fR:
.ie n .IP """size"" (\fB\s-1OSSL_MAC_PARAM_SIZE\s0\fR) <unsigned integer>" 4
.el .IP "``size'' (\fB\s-1OSSL_MAC_PARAM_SIZE\s0\fR) <unsigned integer>" 4
.IX Item "size (OSSL_MAC_PARAM_SIZE) <unsigned integer>"
Gets the \s-1MAC\s0 size.
.PP
The \*(L"size\*(R" parameter can also be retrieved with \fBEVP_MAC_CTX_get_mac_size()\fR.
The length of the \*(L"size\*(R" parameter is equal to that of an \fBunsigned int\fR.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBEVP_MAC_CTX_get_params\fR\|(3), \fBEVP_MAC_CTX_set_params\fR\|(3),
\&\*(L"\s-1PARAMETERS\*(R"\s0 in \s-1\fBEVP_MAC\s0\fR\|(3), \s-1\fBOSSL_PARAM\s0\fR\|(3)
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2018\-2021 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>.