1.\" $NetBSD: hmac.3,v 1.6 2018/05/23 02:08:40 christos Exp $ 2.\" 3.\" Copyright (c) 2016 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to The NetBSD Foundation 7.\" by Christos Zoulas. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 19.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 20.\"TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 21.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 22.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 23.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 24.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 25.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 26.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 27.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 28.\" POSSIBILITY OF SUCH DAMAGE. 29.\" 30.Dd May 22, 2018 31.Dt HMAC 3 32.Os 33.Sh NAME 34.Nm hmac 35.Nd compute a key-Hash Message Authentication Code 36.Sh LIBRARY 37.Lb libc 38.Sh SYNOPSIS 39.In stdlib.h 40.Ft ssize_t 41.Fn hmac "const char *hname" "const void *key" "size_t klen" "const void *text" "size_t tlen" "void *digest" "size_t dlen" 42.Sh DESCRIPTION 43The 44.Fn hmac 45function computes the key-Hash Message Authentication Code per 46.Tn RFC 2104 47and places the result in 48.Fa digest 49writing up to 50.Fa dlen 51bytes. 52The actual number of bytes that would be written is returned. 53.Pp 54The hash functions supported are: md2, md4, md5, rmd160, sha1, sha224, 55sha256, sha384, and sha512. 56.Sh RETURN VALUES 57The 58.Fn hmac 59function returns 60.Dv \-1 61if the 62.Fa hname 63is not found. 64Otherwise the actual length of the digest string is returned (which could 65be bigger or smaller than 66.Fa dlen ) . 67This length depends on the hashing function selected. 68.Sh SEE ALSO 69.Xr md2 3 , 70.Xr md4 3 , 71.Xr md5 3 , 72.Xr openssl_HMAC 3 , 73.Xr openssl_MD2 3 , 74.Xr openssl_MD4 3 , 75.Xr openssl_MD5 3 , 76.Xr rmd160 3 , 77.Xr sha1 3 , 78.Xr sha2 3 79.Sh STANDARDS 80.Rs 81.%R RFC 2104 82.Re 83.Sh NOTES 84The maximum digest length has been extended from 85.Dv 64 86to 87.Dv 128 88bytes to handle SHA2. 89.Sh HISTORY 90The 91.Fn hmac 92function appeared in 93.Nx 8 . 94