path: root/lib/libcrypto/man/HMAC.3

.\"	$OpenBSD: HMAC.3,v 1.4 2016/11/27 15:58:47 schwarze Exp $
.\"	OpenSSL a528d4f0 Oct 27 13:40:11 2015 -0400
.\"
.\" This file was written by Ulf Moeller <ulf@openssl.org>.
.\" Copyright (c) 2000-2002, 2006, 2008, 2009, 2013, 2016 The OpenSSL Project.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\"
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\"
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in
.\"    the documentation and/or other materials provided with the
.\"    distribution.
.\"
.\" 3. All advertising materials mentioning features or use of this
.\"    software must display the following acknowledgment:
.\"    "This product includes software developed by the OpenSSL Project
.\"    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
.\"
.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
.\"    endorse or promote products derived from this software without
.\"    prior written permission. For written permission, please contact
.\"    openssl-core@openssl.org.
.\"
.\" 5. Products derived from this software may not be called "OpenSSL"
.\"    nor may "OpenSSL" appear in their names without prior written
.\"    permission of the OpenSSL Project.
.\"
.\" 6. Redistributions of any form whatsoever must retain the following
.\"    acknowledgment:
.\"    "This product includes software developed by the OpenSSL Project
.\"    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
.\" OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd $Mdocdate: November 27 2016 $
.Dt HMAC 3
.Os
.Sh NAME
.Nm HMAC ,
.Nm HMAC_CTX_init ,
.Nm HMAC_Init ,
.Nm HMAC_Init_ex ,
.Nm HMAC_Update ,
.Nm HMAC_Final ,
.Nm HMAC_CTX_cleanup ,
.Nm HMAC_cleanup
.Nd HMAC message authentication code
.Sh SYNOPSIS
.In openssl/hmac.h
.Ft unsigned char *
.Fo HMAC
.Fa "const EVP_MD *evp_md"
.Fa "const void *key"
.Fa "int key_len"
.Fa "const unsigned char *d"
.Fa "int n"
.Fa "unsigned char *md"
.Fa "unsigned int *md_len"
.Fc
.Ft void
.Fo HMAC_CTX_init
.Fa "HMAC_CTX *ctx"
.Fc
.Ft int
.Fo HMAC_Init
.Fa "HMAC_CTX *ctx"
.Fa "const void *key"
.Fa "int key_len"
.Fa "const EVP_MD *md"
.Fc
.Ft int
.Fo HMAC_Init_ex
.Fa "HMAC_CTX *ctx"
.Fa "const void *key"
.Fa "int key_len"
.Fa "const EVP_MD *md"
.Fa "ENGINE *impl"
.Fc
.Ft int
.Fo HMAC_Update
.Fa "HMAC_CTX *ctx"
.Fa "const unsigned char *data"
.Fa "int len"
.Fc
.Ft int
.Fo HMAC_Final
.Fa "HMAC_CTX *ctx"
.Fa "unsigned char *md"
.Fa "unsigned int *len"
.Fc
.Ft void
.Fo HMAC_CTX_cleanup
.Fa "HMAC_CTX *ctx"
.Fc
.Ft void
.Fo HMAC_cleanup
.Fa "HMAC_CTX *ctx"
.Fc
.Ft int
.Fo HMAC_CTX_copy
.Fa "HMAC_CTX *dctx"
.Fa "HMAC_CTX *sctx"
.Fc
.Ft void
.Fo HMAC_CTX_set_flags
.Fa "HMAC_CTX *ctx"
.Fa "unsigned long flags"
.Fc
.Ft size_t
.Fo HMAC_size
.Fa "const HMAC_CTX *e"
.Fc
.Sh DESCRIPTION
HMAC is a MAC (message authentication code), i.e. a keyed hash
function used for message authentication, which is based on a hash
function.
.Pp
.Fn HMAC
computes the message authentication code of the
.Fa n
bytes at
.Fa d
using the hash function
.Fa evp_md
and the key
.Fa key
which is
.Fa key_len
bytes long.
.Pp
It places the result in
.Fa md ,
which must have space for the output of the hash function, which is no
more than
.Dv EVP_MAX_MD_SIZE
bytes.
If
.Fa md
is
.Dv NULL ,
the digest is placed in a static array.
The size of the output is placed in
.Fa md_len ,
unless it is
.Dv NULL .
.Pp
.Fa evp_md
can be
.Xr EVP_sha1 3 ,
.Xr EVP_ripemd160 3 ,
etc.
.Pp
.Fn HMAC_CTX_init
initialises a
.Vt HMAC_CTX
before first use.
It must be called.
.Pp
.Fn HMAC_CTX_cleanup
erases the key and other data from the
.Vt HMAC_CTX
and releases any associated resources.
It must be called when an
.Vt HMAC_CTX
is no longer required.
.Pp
.Fn HMAC_cleanup
is an alias for
.Fn HMAC_CTX_cleanup
included for backward compatibility with 0.9.6b.
It is deprecated and implemented as a macro.
.Pp
The following functions may be used if the message is not completely
stored in memory:
.Pp
.Fn HMAC_Init
initializes a
.Vt HMAC_CTX
structure to use the hash function
.Fa evp_md
and the key
.Fa key
which is
.Fa key_len
bytes long.
It is deprecated and only included for backward compatibility with
OpenSSL 0.9.6b.
.Pp
.Fn HMAC_Init_ex
initializes or reuses a
.Vt HMAC_CTX
structure to use the function
.Fa evp_md
and key
.Fa key .
Either can be
.Dv NULL ,
in which case the existing one will be reused.
.Fn HMAC_CTX_init
must have been called before the first use of an
.Vt HMAC_CTX
in this function.
.Sy N.B.
.Fn HMAC_Init
had this undocumented behaviour in previous versions of OpenSSL -
failure to switch to
.Fn HMAC_Init_ex
in programs that expect it will cause them to stop working.
.Pp
.Fn HMAC_Update
can be called repeatedly with chunks of the message to be authenticated
.Pq Fa len No bytes at Fa data .
.Pp
.Fn HMAC_Final
places the message authentication code in
.Fa md ,
which must have space for the hash function output.
.Pp
.Fn HMAC_CTX_copy
copies all of the internal state from
.Fa sctx
into
.Fa dctx .
.Pp
.Fn HMAC_CTX_set_flags
applies the specified flags to the internal
.Vt EVP_MD_CTX Ns s.
These flags have the same meaning as for
.Xr EVP_MD_CTX_set_flags 3 .
.Pp
.Fn HMAC_size
returns the length in bytes of the underlying hash function output.
It is implemented as a macro.
.Sh RETURN VALUES
.Fn HMAC
returns a pointer to the message authentication code or
.Dv NULL
if an error occurred.
.Pp
.Fn HMAC_Init_ex ,
.Fn HMAC_Update ,
.Fn HMAC_Final ,
and
.Fn HMAC_CTX_copy
return 1 for success or 0 if an error occurred.
.Pp
.Fn HMAC_size
returns the length in bytes of the underlying hash function output
or 0 on error.
.Sh SEE ALSO
.Xr evp 3
.Sh STANDARDS
RFC 2104
.Sh HISTORY
.Fn HMAC ,
.Fn HMAC_Init ,
.Fn HMAC_Update ,
.Fn HMAC_Final ,
and
.Fn HMAC_cleanup
are available since SSLeay 0.9.0.
.Pp
.Fn HMAC_CTX_init ,
.Fn HMAC_Init_ex ,
and
.Fn HMAC_CTX_cleanup
are available since OpenSSL 0.9.7.
.Pp
.Fn HMAC_Init_ex ,
.Fn HMAC_Update ,
and
.Fn HMAC_Final
did not return values in versions of OpenSSL before 1.0.0.