Android_verify/third_party/android-libs/share/man/man3/HMAC.3ossl

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.\" ========================================================================
.\"
.IX Title "HMAC 3ossl"
.TH HMAC 3ossl "2024-09-03" "3.3.2" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
HMAC,
HMAC_CTX_new,
HMAC_CTX_reset,
HMAC_CTX_free,
HMAC_Init,
HMAC_Init_ex,
HMAC_Update,
HMAC_Final,
HMAC_CTX_copy,
HMAC_CTX_set_flags,
HMAC_CTX_get_md,
HMAC_size
\&\- HMAC message authentication code
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/hmac.h>
\&
\& unsigned char *HMAC(const EVP_MD *evp_md, const void *key, int key_len,
\&                     const unsigned char *data, size_t data_len,
\&                     unsigned char *md, unsigned int *md_len);
.Ve
.PP
The following functions have been deprecated since OpenSSL 3.0, and can be
hidden entirely by defining \fB\s-1OPENSSL_API_COMPAT\s0\fR with a suitable version value,
see \fBopenssl_user_macros\fR\|(7):
.PP
.Vb 2
\& HMAC_CTX *HMAC_CTX_new(void);
\& int HMAC_CTX_reset(HMAC_CTX *ctx);
\&
\& int HMAC_Init_ex(HMAC_CTX *ctx, const void *key, int key_len,
\&                  const EVP_MD *md, ENGINE *impl);
\& int HMAC_Update(HMAC_CTX *ctx, const unsigned char *data, size_t len);
\& int HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len);
\&
\& void HMAC_CTX_free(HMAC_CTX *ctx);
\&
\& int HMAC_CTX_copy(HMAC_CTX *dctx, HMAC_CTX *sctx);
\& void HMAC_CTX_set_flags(HMAC_CTX *ctx, unsigned long flags);
\& const EVP_MD *HMAC_CTX_get_md(const HMAC_CTX *ctx);
\&
\& size_t HMAC_size(const HMAC_CTX *e);
.Ve
.PP
The following function has been deprecated since OpenSSL 1.1.0, and can be
hidden entirely by defining \fB\s-1OPENSSL_API_COMPAT\s0\fR with a suitable version value,
see \fBopenssl_user_macros\fR\|(7):
.PP
.Vb 2
\& int HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len,
\&               const EVP_MD *md);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\s-1HMAC\s0 is a \s-1MAC\s0 (message authentication code), i.e. a keyed hash
function used for message authentication, which is based on a hash
function.
.PP
\&\s-1\fBHMAC\s0()\fR computes the message authentication code of the \fIdata_len\fR bytes at
\&\fIdata\fR using the hash function \fIevp_md\fR and the key \fIkey\fR which is
\&\fIkey_len\fR bytes long. The \fIkey\fR may also be \s-1NULL\s0 with \fIkey_len\fR being 0.
.PP
It places the result in \fImd\fR (which must have space for the output of
the hash function, which is no more than \fB\s-1EVP_MAX_MD_SIZE\s0\fR bytes).
If \fImd\fR is \s-1NULL,\s0 the digest is placed in a static array.  The size of
the output is placed in \fImd_len\fR, unless it is \s-1NULL.\s0 Note: passing a \s-1NULL\s0
value for \fImd\fR to use the static array is not thread safe.
.PP
\&\fIevp_md\fR is a message digest such as \fBEVP_sha1()\fR, \fBEVP_ripemd160()\fR etc.
\&\s-1HMAC\s0 does not support variable output length digests such as \fBEVP_shake128()\fR and
\&\fBEVP_shake256()\fR.
.PP
\&\s-1\fBHMAC\s0()\fR uses the default \fB\s-1OSSL_LIB_CTX\s0\fR.
Use \fBEVP_Q_mac\fR\|(3) instead if a library context is required.
.PP
All of the functions described below are deprecated.
Applications should instead use \fBEVP_MAC_CTX_new\fR\|(3), \fBEVP_MAC_CTX_free\fR\|(3),
\&\fBEVP_MAC_init\fR\|(3), \fBEVP_MAC_update\fR\|(3) and \fBEVP_MAC_final\fR\|(3)
or the 'quick' single-shot \s-1MAC\s0 function \fBEVP_Q_mac\fR\|(3).
.PP
\&\fBHMAC_CTX_new()\fR creates a new \s-1HMAC_CTX\s0 in heap memory.
.PP
\&\fBHMAC_CTX_reset()\fR clears an existing \fB\s-1HMAC_CTX\s0\fR and associated
resources, making it suitable for new computations as if it was newly
created with \fBHMAC_CTX_new()\fR.
.PP
\&\fBHMAC_CTX_free()\fR erases the key and other data from the \fB\s-1HMAC_CTX\s0\fR,
releases any associated resources and finally frees the \fB\s-1HMAC_CTX\s0\fR
itself. If the argument is \s-1NULL,\s0 nothing is done.
.PP
The following functions may be used if the message is not completely
stored in memory:
.PP
\&\fBHMAC_Init_ex()\fR initializes or reuses a \fB\s-1HMAC_CTX\s0\fR structure to use the hash
function \fIevp_md\fR and key \fIkey\fR. If both are \s-1NULL,\s0 or if \fIkey\fR is \s-1NULL\s0
and \fIevp_md\fR is the same as the previous call, then the
existing key is
reused. \fIctx\fR must have been created with \fBHMAC_CTX_new()\fR before the first use
of an \fB\s-1HMAC_CTX\s0\fR in this function.
.PP
If \fBHMAC_Init_ex()\fR is called with \fIkey\fR \s-1NULL\s0 and \fIevp_md\fR is not the
same as the previous digest used by \fIctx\fR then an error is returned
because reuse of an existing key with a different digest is not supported.
.PP
\&\fBHMAC_Init()\fR initializes a \fB\s-1HMAC_CTX\s0\fR structure to use the hash
function \fIevp_md\fR and the key \fIkey\fR which is \fIkey_len\fR bytes
long.
.PP
\&\fBHMAC_Update()\fR can be called repeatedly with chunks of the message to
be authenticated (\fIlen\fR bytes at \fIdata\fR).
.PP
\&\fBHMAC_Final()\fR places the message authentication code in \fImd\fR, which
must have space for the hash function output.
.PP
\&\fBHMAC_CTX_copy()\fR copies all of the internal state from \fIsctx\fR into \fIdctx\fR.
.PP
\&\fBHMAC_CTX_set_flags()\fR applies the specified flags to the internal EVP_MD_CTXs.
These flags have the same meaning as for \fBEVP_MD_CTX_set_flags\fR\|(3).
.PP
\&\fBHMAC_CTX_get_md()\fR returns the \s-1EVP_MD\s0 that has previously been set for the
supplied \s-1HMAC_CTX.\s0
.PP
\&\fBHMAC_size()\fR returns the length in bytes of the underlying hash function output.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\s-1\fBHMAC\s0()\fR returns a pointer to the message authentication code or \s-1NULL\s0 if
an error occurred.
.PP
\&\fBHMAC_CTX_new()\fR returns a pointer to a new \fB\s-1HMAC_CTX\s0\fR on success or
\&\s-1NULL\s0 if an error occurred.
.PP
\&\fBHMAC_CTX_reset()\fR, \fBHMAC_Init_ex()\fR, \fBHMAC_Update()\fR, \fBHMAC_Final()\fR and
\&\fBHMAC_CTX_copy()\fR return 1 for success or 0 if an error occurred.
.PP
\&\fBHMAC_CTX_get_md()\fR return the \s-1EVP_MD\s0 previously set for the supplied \s-1HMAC_CTX\s0 or
\&\s-1NULL\s0 if no \s-1EVP_MD\s0 has been set.
.PP
\&\fBHMAC_size()\fR returns the length in bytes of the underlying hash function output
or zero on error.
.SH "CONFORMING TO"
.IX Header "CONFORMING TO"
\&\s-1RFC 2104\s0
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\s-1\fBSHA1\s0\fR\|(3), \fBEVP_Q_mac\fR\|(3), \fBevp\fR\|(7)
.SH "HISTORY"
.IX Header "HISTORY"
All functions except for \s-1\fBHMAC\s0()\fR were deprecated in OpenSSL 3.0.
.PP
\&\fBHMAC_CTX_init()\fR was replaced with \fBHMAC_CTX_reset()\fR in OpenSSL 1.1.0.
.PP
\&\fBHMAC_CTX_cleanup()\fR existed in OpenSSL before version 1.1.0.
.PP
\&\fBHMAC_CTX_new()\fR, \fBHMAC_CTX_free()\fR and \fBHMAC_CTX_get_md()\fR are new in OpenSSL 1.1.0.
.PP
\&\fBHMAC_Init_ex()\fR, \fBHMAC_Update()\fR and \fBHMAC_Final()\fR did not return values in
OpenSSL before version 1.0.0.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2000\-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>.