1.\" FreeSec: libcrypt for NetBSD 2.\" 3.\" Copyright (c) 1994 David Burren 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 4. Neither the name of the author nor the names of other contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" $FreeBSD: src/lib/libcrypt/crypt.3,v 1.6.2.14 2002/12/29 16:35:35 schweikh Exp $ 31.\" $DragonFly: src/lib/libcrypt/crypt.3,v 1.5 2006/03/26 22:56:56 swildner Exp $ 32.\" 33.\" Manual page, using -mandoc macros 34.\" 35.Dd January 19, 1997 36.Dt CRYPT 3 37.Os 38.Sh NAME 39.Nm crypt 40.Nd Trapdoor encryption 41.Sh LIBRARY 42.Lb libcrypt 43.Sh SYNOPSIS 44.In unistd.h 45.Ft char * 46.Fn crypt "const char *key" "const char *salt" 47.Ft const char * 48.Fn crypt_get_format "void" 49.Ft int 50.Fn crypt_set_format "const char *string" 51.Sh DESCRIPTION 52The 53.Fn crypt 54function performs password hashing with additional code added to 55deter key search attempts. Different algorithms can be used to 56in the hash. 57.\" 58.\" NOTICE: 59.\" If you add more algorithms, make sure to update this list 60.\" and the default used for the Traditional format, below. 61.\" 62Currently these include the 63.Tn NBS 64.Tn Data Encryption Standard (DES) , 65.Tn MD5 66and 67.Tn Blowfish . 68The algorithm used will depend upon the format of the Salt (following 69the Modular Crypt Format (MCF)), if 70.Tn DES 71and/or 72.Tn Blowfish 73is installed or not, and whether 74.Fn crypt_set_format 75has been called to change the default. 76.Pp 77The first argument to 78.Nm 79is the data to hash (usually a password), in a 80.Dv null Ns -terminated 81string. 82The second is the salt, in one of three forms: 83.Pp 84.Bl -tag -width Traditional -compact -offset indent 85.It Extended 86If it begins with an underscore 87.Pq Dq _ 88then the 89.Tn DES 90Extended Format 91is used in interpreting both the key and the salt, as outlined below. 92.It Modular 93If it begins with the string 94.Dq $digit$ 95then the Modular Crypt Format is used, as outlined below. 96.It Traditional 97If neither of the above is true, it assumes the Traditional Format, 98using the entire string as the salt (or the first portion). 99.El 100.Pp 101All routines are designed to be time-consuming. A brief test on a 102.Tn Pentium 103166/MMX shows the 104.Tn DES 105crypt to do approximately 2640 crypts 106a CPU second and MD5 to do about 62 crypts a CPU second. 107.Ss DES Extended Format: 108The 109.Ar key 110is divided into groups of 8 characters (the last group is null-padded) 111and the low-order 7 bits of each character (56 bits per group) are 112used to form the 113.Tn DES 114key as follows: 115the first group of 56 bits becomes the initial 116.Tn DES 117key. 118For each additional group, the XOR of the encryption of the current 119.Tn DES 120key with itself and the group bits becomes the next 121.Tn DES 122key. 123.Pp 124The salt is a 9-character array consisting of an underscore followed 125by 4 bytes of iteration count and 4 bytes of salt. 126These are encoded as printable characters, 6 bits per character, 127least significant character first. 128The values 0 to 63 are encoded as ``./0-9A-Za-z''. 129This allows 24 bits for both 130.Fa count 131and 132.Fa salt . 133.Pp 134The 135.Fa salt 136introduces disorder in the 137.Tn DES 138algorithm in one of 16777216 or 4096 possible ways 139(ie. with 24 or 12 bits: if bit 140.Em i 141of the 142.Ar salt 143is set, then bits 144.Em i 145and 146.Em i+24 147are swapped in the 148.Tn DES 149E-box output). 150.Pp 151The 152.Tn DES 153key is used to encrypt a 64-bit constant using 154.Ar count 155iterations of 156.Tn DES . 157The value returned is a 158.Dv null Ns -terminated 159string, 20 or 13 bytes (plus null) in length, consisting of the 160.Ar salt 161followed by the encoded 64-bit encryption. 162.Ss "Modular" crypt: 163If the salt begins with the string 164.Fa $digit$ 165then the Modular Crypt Format is used. The 166.Fa digit 167represents which algorithm is used in encryption. Following the token is 168the actual salt to use in the encryption. The length of the salt is limited 169to 8 characters--because the length of the returned output is also limited 170(_PASSWORD_LEN). The salt must be terminated with the end of the string 171(NULL) or a dollar sign. Any characters after the dollar sign are ignored. 172.Pp 173Currently supported algorithms are: 174.Pp 175.Bl -enum -compact -offset indent 176.It 177MD5 178.It 179Blowfish 180.El 181.Pp 182Other crypt formats may be easily added. An example salt would be: 183.Bl -tag -offset indent 184.It Cm "$3$thesalt$rest" 185.El 186.Ss "Traditional" crypt: 187The algorithm used will depend upon whether 188.Fn crypt_set_format 189has been called and whether a global default format has been specified. 190Unless a global default has been specified or 191.Fn crypt_set_format 192has set the format to something else, the built-in default format is 193used. 194This is currently 195.\" 196.\" NOTICE: Also make sure to update this 197.\" 198DES 199if it is available, or MD5 if not. 200.Pp 201How the salt is used will depend upon the algorithm for the hash. For 202best results, specify at least two characters of salt. 203.Pp 204The 205.Fn crypt_get_format 206function returns a constant string that represents the name of the 207algorithm currently used. 208Valid values are 209.\" 210.\" NOTICE: Also make sure to update this, too, as well 211.\" 212.Ql des , 213.Ql blf 214and 215.Ql md5 . 216.Pp 217The 218.Fn crypt_set_format 219function sets the default encoding format according to the supplied 220.Fa string . 221.Pp 222The global default format can be set using the 223.Pa /etc/auth.conf 224file using the 225.Va crypt_default 226property. 227.Sh RETURN VALUES 228.Fn crypt 229returns a pointer to the encrypted value on success, and NULL on failure. 230Note: this is not a standard behaviour, AT&T 231.Fn crypt 232will always return a pointer to a string. 233.Pp 234.Fn crypt_set_format 235will return 1 if the supplied encoding format was valid. 236Otherwise, a value of 0 is returned. 237.Sh SEE ALSO 238.Xr login 1 , 239.Xr passwd 1 , 240.Xr auth_getval 3 , 241.Xr cipher 3 , 242.Xr getpass 3 , 243.Xr auth.conf 5 , 244.Xr passwd 5 245.Sh HISTORY 246A rotor-based 247.Fn crypt 248function appeared in 249.At v6 . 250The current style 251.Fn crypt 252first appeared in 253.At v7 . 254.Pp 255The 256.Tn DES 257section of the code (FreeSec 1.0) was developed outside the United 258States of America as an unencumbered replacement for the U.S.-only 259.Nx 260libcrypt encryption library. 261.Sh AUTHORS 262.An -nosplit 263Originally written by 264.An David Burren Aq davidb@werj.com.au , 265later additions and changes by 266.An Poul-Henning Kamp , 267.An Mark R V Murray , 268.An Kris Kennaway , 269.An Brian Feldman , 270.An Paul Herman 271and 272.An Niels Provos . 273.Sh BUGS 274The 275.Fn crypt 276function returns a pointer to static data, and subsequent calls to 277.Fn crypt 278will modify the same data. Likewise, 279.Fn crypt_set_format 280modifies static data. 281