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.\" $FreeBSD$ 31.\" 32.\" Manual page, using -mandoc macros 33.\" 34.Dd January 19, 1997 35.Dt CRYPT 3 36.Os "FreeSec 1.0" 37.Sh NAME 38.Nm crypt 39.Nd Trapdoor encryption 40.Sh LIBRARY 41.Lb libcrypt 42.Sh SYNOPSIS 43.Fd #include <unistd.h> 44.Ft char * 45.Fn crypt "const char *key" "const char *salt" 46.Ft const char * 47.Fn crypt_get_format "void" 48.Ft int 49.Fn crypt_set_format "const char *string" 50.Sh DESCRIPTION 51The 52.Fn crypt 53function performs password hashing with additional code added to 54deter key search attempts. Different algorithms can be used to 55in the hash. 56.\" 57.\" NOTICE: 58.\" If you add more algorithms, make sure to update this list 59.\" and the default used for the Traditional format, below. 60.\" 61Currently these include the 62.Tn NBS 63.Tn Data Encryption Standard (DES) , 64and 65.Tn MD5 . 66The algorithm used will depend upon the format of the Salt (following 67the Modular Crypt Format (MCF)), if 68.Tn DES 69is installed or not, and whether 70.Fn crypt_set_format 71has been called to change the default. 72.Pp 73The first argument to 74.Nm 75is the data to hash (usually a password), in a 76.Dv null Ns -terminated 77string. 78The second is the salt, in one of three forms: 79.Pp 80.Bl -tag -width Traditional -compact -offset indent 81.It Extended 82If it begins with an underscore 83.Pq Dq _ 84then the 85.Tn DES 86Extended Format 87is used in interpreting both the the key and the salt, as outlined below. 88.It Modular 89If it begins with the string 90.Dq $digit$ 91then the Modular Crypt Format is used, as outlined below. 92.It Traditional 93If neither of the above is true, it assumes the Traditional Format, 94using the entire string as the salt (or the first portion). 95.El 96.Pp 97All routines are designed to be time-consuming. A brief test on a 98.Tn Pentium 99166/MMX shows the 100.Tn DES 101crypt to do approximately 2640 crypts 102a CPU second and MD5 to do about 62 crypts a CPU second. 103.Ss DES Extended Format: 104.Pp 105The 106.Ar key 107is divided into groups of 8 characters (the last group is null-padded) 108and the low-order 7 bits of each each character (56 bits per group) are 109used to form the 110.Tn DES 111key as follows: 112the first group of 56 bits becomes the initial 113.Tn DES 114key. 115For each additional group, the XOR of the encryption of the current 116.Tn DES 117key with itself and the group bits becomes the next 118.Tn DES 119key. 120.Pp 121The salt is a 9-character array consisting of an underscore followed 122by 4 bytes of iteration count and 4 bytes of salt. 123These are encoded as printable characters, 6 bits per character, 124least significant character first. 125The values 0 to 63 are encoded as ``./0-9A-Za-z''. 126This allows 24 bits for both 127.Fa count 128and 129.Fa salt . 130.Pp 131The 132.Fa salt 133introduces disorder in the 134.Tn DES 135algorithm in one of 16777216 or 4096 possible ways 136(ie. with 24 or 12 bits: if bit 137.Em i 138of the 139.Ar salt 140is set, then bits 141.Em i 142and 143.Em i+24 144are swapped in the 145.Tn DES 146E-box output). 147.Pp 148The 149.Tn DES 150key is used to encrypt a 64-bit constant using 151.Ar count 152iterations of 153.Tn DES . 154The value returned is a 155.Dv null Ns -terminated 156string, 20 or 13 bytes (plus null) in length, consisting of the 157.Ar salt 158followed by the encoded 64-bit encryption. 159.Ss "Modular" crypt: 160.Pp 161If the salt begins with the string 162.Fa $digit$ 163then the Modular Crypt Format is used. The 164.Fa digit 165represents which algorithm is used in encryption. Following the token is 166the actual salt to use in the encryption. The length of the salt is limited 167to 16 characters--because the length of the returned output is also limited 168(_PASSWORD_LEN). The salt must be terminated with the end of the string 169(NULL) or a dollar sign. Any characters after the dollar sign are ignored. 170.Pp 171Currently supported algorithms are: 172.Pp 173.Bl -tag -width 012345678 -compact -offset indent 174.It 1 175MD5 176.El 177.Pp 178Other crypt formats may be easilly added. An example salt would be: 179.Bl -tag -offset indent 180.It Cm "$3$thesalt$rest" 181.El 182.Pp 183.Ss "Traditional" crypt: 184.Pp 185The algorithm used will depend upon whether 186.Fn crypt_set_format 187has been called and whether 188.Tn DES 189is installed or not. If 190.Tn DES 191is installed and 192.Fn crypt_set_format 193has not set the format to something else, it will be used. 194Otherwise, the best algorithm is used, which is currently 195.\" 196.\" NOTICE: Also make sure to update this 197.\" 198MD5. 199.Pp 200How the salt is used will depend upon the algorithm for the hash. For 201best results, specify at least two characters of salt. 202.Pp 203The 204.Fn crypt_get_format 205function returns a constant string that represents the name of the 206algorithm currently used. 207Valid values are 208.\" 209.\" NOTICE: Also make sure to update this, too, as well 210.\" 211.Ql des 212and 213.Ql md5 . 214.Pp 215The 216.Fn crypt_set_format 217function sets the default encoding format according to the supplied 218.Fa string . 219.Sh RETURN VALUES 220.Pp 221.Fn crypt 222returns a pointer to the encrypted value on success, and NULL on failure. 223Note: this is not a standard behaviour, AT&T 224.Fn crypt 225will always return a pointer to a string. 226.Pp 227.Fn crypt_set_format 228will return 1 if the supplied encoding format was valid. 229Otherwise, a value of 0 is returned. 230.Sh SEE ALSO 231.Xr login 1 , 232.Xr passwd 1 , 233.Xr cipher 3 , 234.Xr getpass 3 , 235.Xr passwd 5 , 236.Sh BUGS 237The 238.Fn crypt 239function returns a pointer to static data, and subsequent calls to 240.Fn crypt 241will modify the same data. Likewise, 242.Fn crypt_set_format 243modifies static data. 244.Sh HISTORY 245A rotor-based 246.Fn crypt 247function appeared in 248.At v6 . 249The current style 250.Fn crypt 251first appeared in 252.At v7 . 253.Pp 254The 255.Tn DES 256section of the code (FreeSec 1.0) was developed outside the United 257States of America as an unencumbered replacement for the U.S.-only 258.Nx 259libcrypt encryption library. 260Users should be aware that this code (and programs staticly linked with it) 261may not be exported from the U.S., although it apparently can be imported. 262.Sh AUTHORS 263.An -nosplit 264Originally written by 265.An David Burren Aq davidb@werj.com.au , 266later additions and changes by 267.An Poul-Henning Kamp , 268.An Mark R V Murray , 269.An Kris Kennaway 270and 271.An Brian Feldman . 272