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.\" ========================================================================
.\"
.IX Title "hmac 3openssl"
.TH hmac 3openssl "2016-06-23" "1.0.1t" "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_init, HMAC_Init, HMAC_Init_ex, HMAC_Update, HMAC_Final, HMAC_CTX_cleanup, HMAC_cleanup \- 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 *d, int n,
\&               unsigned char *md, unsigned int *md_len);
\&
\& void HMAC_CTX_init(HMAC_CTX *ctx);
\&
\& int HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len,
\&               const EVP_MD *md);
\& 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, int len);
\& int HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len);
\&
\& void HMAC_CTX_cleanup(HMAC_CTX *ctx);
\& void HMAC_cleanup(HMAC_CTX *ctx);
.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\fIHMAC\s0()\fR computes the message authentication code of the \fBn\fR bytes at
\&\fBd\fR using the hash function \fBevp_md\fR and the key \fBkey\fR which is
\&\fBkey_len\fR bytes long.
.PP
It places the result in \fBmd\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 \fBmd\fR is \s-1NULL\s0, the digest is placed in a static array.  The size of
the output is placed in \fBmd_len\fR, unless it is \fB\s-1NULL\s0\fR.
.PP
\&\fBevp_md\fR can be \fIEVP_sha1()\fR, \fIEVP_ripemd160()\fR etc.
.PP
\&\fIHMAC_CTX_init()\fR initialises a \fB\s-1HMAC_CTX\s0\fR before first use. It must be
called.
.PP
\&\fIHMAC_CTX_cleanup()\fR erases the key and other data from the \fB\s-1HMAC_CTX\s0\fR
and releases any associated resources. It must be called when an
\&\fB\s-1HMAC_CTX\s0\fR is no longer required.
.PP
\&\fIHMAC_cleanup()\fR is an alias for \fIHMAC_CTX_cleanup()\fR included for back
compatibility with 0.9.6b, it is deprecated.
.PP
The following functions may be used if the message is not completely
stored in memory:
.PP
\&\fIHMAC_Init()\fR initializes a \fB\s-1HMAC_CTX\s0\fR structure to use the hash
function \fBevp_md\fR and the key \fBkey\fR which is \fBkey_len\fR bytes
long. It is deprecated and only included for backward compatibility
with OpenSSL 0.9.6b.
.PP
\&\fIHMAC_Init_ex()\fR initializes or reuses a \fB\s-1HMAC_CTX\s0\fR structure to use
the function \fBevp_md\fR and key \fBkey\fR. Either can be \s-1NULL\s0, in which
case the existing one will be reused. \fIHMAC_CTX_init()\fR must have been
called before the first use of an \fB\s-1HMAC_CTX\s0\fR in this
function. \fBN.B. \f(BIHMAC_Init()\fB had this undocumented behaviour in
previous versions of OpenSSL \- failure to switch to \f(BIHMAC_Init_ex()\fB in
programs that expect it will cause them to stop working\fR.
.PP
\&\fIHMAC_Update()\fR can be called repeatedly with chunks of the message to
be authenticated (\fBlen\fR bytes at \fBdata\fR).
.PP
\&\fIHMAC_Final()\fR places the message authentication code in \fBmd\fR, which
must have space for the hash function output.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\s-1\fIHMAC\s0()\fR returns a pointer to the message authentication code or \s-1NULL\s0 if
an error occurred.
.PP
\&\fIHMAC_Init_ex()\fR, \fIHMAC_Update()\fR and \fIHMAC_Final()\fR return 1 for success or 0 if
an error occurred.
.PP
\&\fIHMAC_CTX_init()\fR and \fIHMAC_CTX_cleanup()\fR do not return values.
.SH "CONFORMING TO"
.IX Header "CONFORMING TO"
\&\s-1RFC\s0 2104

.\" Oracle has added the ARC stability level to this manual page
.SH ATTRIBUTES
See
.BR attributes (5)
for descriptions of the following attributes:
.sp
.TS
box;
cbp-1 | cbp-1
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE 
=
Availability	library/security/openssl
=
Stability	Uncommitted
.TE 
.PP
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIsha\fR\|(3), \fIevp\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
\&\s-1\fIHMAC\s0()\fR, \fIHMAC_Init()\fR, \fIHMAC_Update()\fR, \fIHMAC_Final()\fR and \fIHMAC_cleanup()\fR
are available since SSLeay 0.9.0.
.PP
\&\fIHMAC_CTX_init()\fR, \fIHMAC_Init_ex()\fR and \fIHMAC_CTX_cleanup()\fR are available
since OpenSSL 0.9.7.
.PP
\&\fIHMAC_Init_ex()\fR, \fIHMAC_Update()\fR and \fIHMAC_Final()\fR did not return values in
versions of OpenSSL before 1.0.0.


.SH NOTES

.\" Oracle has added source availability information to this manual page
This software was built from source available at https://java.net/projects/solaris-userland.  The original community source was downloaded from  http://www.openssl.org/source/openssl-1.0.1t.tar.gz

Further information about this software can be found on the open source community website at http://www.openssl.org/.