1.\" $OpenBSD: PKCS5_PBKDF2_HMAC.3,v 1.9 2019/06/07 20:46:25 schwarze Exp $ 2.\" OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100 3.\" 4.\" This file was written by Jeffrey Walton <noloader@gmail.com>. 5.\" Copyright (c) 2014, 2015 The OpenSSL Project. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in 16.\" the documentation and/or other materials provided with the 17.\" distribution. 18.\" 19.\" 3. 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Redistributions of any form whatsoever must retain the following 34.\" acknowledgment: 35.\" "This product includes software developed by the OpenSSL Project 36.\" for use in the OpenSSL Toolkit (http://www.openssl.org/)" 37.\" 38.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY 39.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 40.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 41.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR 42.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 43.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 44.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 45.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 46.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 47.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 48.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED 49.\" OF THE POSSIBILITY OF SUCH DAMAGE. 50.\" 51.Dd $Mdocdate: June 7 2019 $ 52.Dt PKCS5_PBKDF2_HMAC 3 53.Os 54.Sh NAME 55.Nm PKCS5_PBKDF2_HMAC , 56.Nm PKCS5_PBKDF2_HMAC_SHA1 57.Nd password based derivation routines with salt and iteration count 58.Sh SYNOPSIS 59.In openssl/evp.h 60.Ft int 61.Fo PKCS5_PBKDF2_HMAC 62.Fa "const char *pass" 63.Fa "int passlen" 64.Fa "const unsigned char *salt" 65.Fa "int saltlen" 66.Fa "int iter" 67.Fa "const EVP_MD *digest" 68.Fa "int keylen" 69.Fa "unsigned char *out" 70.Fc 71.Ft int 72.Fo PKCS5_PBKDF2_HMAC_SHA1 73.Fa "const char *pass" 74.Fa "int passlen" 75.Fa "const unsigned char *salt" 76.Fa "int saltlen" 77.Fa "int iter" 78.Fa "int keylen" 79.Fa "unsigned char *out" 80.Fc 81.Sh DESCRIPTION 82.Fn PKCS5_PBKDF2_HMAC 83derives a key from a password using a salt and iteration count as 84specified in RFC 2898. 85.Pp 86.Fa pass 87is the password used in the derivation of length 88.Fa passlen . 89.Fa pass 90is an optional parameter and can be 91.Dv NULL . 92If 93.Fa passlen 94is -1, then the function will calculate the length of 95.Fa pass 96using 97.Xr strlen 3 . 98.Pp 99.Fa salt 100is the salt used in the derivation of length 101.Fa saltlen . 102If the 103.Fa salt 104is 105.Dv NULL , 106then 107.Fa saltlen 108must be 0. 109The function will not attempt to calculate the length of the 110.Fa salt 111because it is not assumed to be NUL terminated. 112.Pp 113.Fa iter 114is the iteration count and its value should be greater than or equal to 1. 115RFC 2898 suggests an iteration count of at least 1000. 116Any 117.Fa iter 118less than 1 is treated as a single iteration. 119.Pp 120.Fa digest 121is the message digest function used in the derivation. 122Values include any of the EVP_* message digests. 123.Fn PKCS5_PBKDF2_HMAC_SHA1 124calls 125.Fn PKCS5_PBKDF2_HMAC 126with 127.Xr EVP_sha1 3 . 128.Pp 129The derived key will be written to 130.Fa out . 131The size of the 132.Fa out 133buffer is specified via 134.Fa keylen . 135.Pp 136A typical application of this function is to derive keying material for 137an encryption algorithm from a password in the 138.Fa pass , 139a salt in 140.Fa salt , 141and an iteration count. 142.Pp 143Increasing the 144.Fa iter 145parameter slows down the algorithm which makes it harder for an attacker 146to perform a brute force attack using a large number of candidate 147passwords. 148.Sh RETURN VALUES 149.Fn PKCS5_PBKDF2_HMAC 150and 151.Fn PBKCS5_PBKDF2_HMAC_SHA1 152return 1 on success or 0 on error. 153.Sh SEE ALSO 154.Xr EVP_BytesToKey 3 , 155.Xr EVP_DigestInit 3 156.Sh HISTORY 157.Fn PKCS5_PBKDF2_HMAC_SHA1 158first appeared in OpenSSL 0.9.4 and has been available since 159.Ox 2.6 . 160.Pp 161.Fn PKCS5_PBKDF2_HMAC 162first appeared in OpenSSL 1.0.0 and has been available since 163.Ox 4.9 . 164