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 SYNOPSIS 41.Ft char 42.Fn *crypt "const char *key" "const char *salt" 43.Sh DESCRIPTION 44The 45.Fn crypt 46function performs password hashing with additional code added to 47deter key search attempts. Different algorithms can be used to 48in the hash. 49.\" 50.\" NOTICE: 51.\" If you add more algorithms, make sure to update this list 52.\" and the default used for the Traditional format, below. 53.\" 54Currently these include the 55.Tn NBS 56Data Encryption Standard (DES), MD5 or SHS. The algorithm 57used will depend upon the format of the Salt--following the Modular 58Crypt Format (MCF)--and if DES is installed or not. 59.Pp 60The first argument to 61.Nm crypt 62is the data to hash (usually a password), in a 63.Dv null Ns -terminated 64string. 65The second is the salt, in one of three forms: 66.Pp 67.Bl -tag -width Traditional -compact -offset indent 68.It Extended 69If it begins with an underscore (``_'') then the DES Extended Format 70is used in interpreting both the the key and the salt, as outlined below. 71.It Modular 72If it begins with the string ``$digit$'' then the Modular Crypt Format 73is used, as outlined below. 74.It Traditional 75If neither of the above is true, it assumes the Traditional Format, 76using the entire string as the salt (or the first portion). 77.El 78.Pp 79All routines are designed to be time-consuming. A brief test on a 80Pentium 166/MMX shows the DES crypt to do approximately 2640 crypts 81a CPU second, MD5 to do about 62 crypts a CPU second and SHA1 82to do about 18 crypts a CPU second. 83.Ss DES Extended Format: 84.Pp 85The 86.Ar key 87is divided into groups of 8 characters (the last group is null-padded) 88and the low-order 7 bits of each each character (56 bits per group) are 89used to form the DES key as follows: 90the first group of 56 bits becomes the initial DES key. 91For each additional group, the XOR of the encryption of the current DES 92key with itself and the group bits becomes the next DES key. 93.Pp 94The salt is a 9-character array consisting of an underscore followed 95by 4 bytes of iteration count and 4 bytes of salt. 96These are encoded as printable characters, 6 bits per character, 97least significant character first. 98The values 0 to 63 are encoded as ``./0-9A-Za-z''. 99This allows 24 bits for both 100.Fa count 101and 102.Fa salt . 103.Pp 104The 105.Fa salt 106introduces disorder in the 107.Tn DES 108algorithm in one of 16777216 or 4096 possible ways 109(ie. with 24 or 12 bits: if bit 110.Em i 111of the 112.Ar salt 113is set, then bits 114.Em i 115and 116.Em i+24 117are swapped in the 118.Tn DES 119E-box output). 120.Pp 121The DES key is used to encrypt a 64-bit constant using 122.Ar count 123iterations of 124.Tn DES . 125The value returned is a 126.Dv null Ns -terminated 127string, 20 or 13 bytes (plus null) in length, consisting of the 128.Ar salt 129followed by the encoded 64-bit encryption. 130.Ss "Modular" crypt: 131.Pp 132If the salt begins with the string 133.Fa $digit$ 134then the Modular Crypt Format is used. The 135.Fa digit 136represents which algorithm is used in encryption. Following the token is 137the actual salt to use in the encryption. The length of the salt is limited 138to 16 characters--because the length of the returned output is also limited 139(_PASSWORD_LEN). The salt must be terminated with the end of the string 140(NULL) or a dollar sign. Any characters after the dollar sign are ignored. 141.Pp 142Currently supported algorithms are: 143.Pp 144.Bl -tag -width 012345678 -compact -offset indent 145.It 1 146MD5 147.It 3 148SHA1 149.El 150.Pp 151Other crypt formats may be easilly added. An example salt would be: 152.Bl -tag -offset indent 153.It Cm "$3$thesalt$rest" 154.El 155.Pp 156.Ss "Traditional" crypt: 157.Pp 158The algorithm used will depend upon whether DES is installed or not. If it is, 159DES will be used. Otherwise, the best algorithm is used, which is currently 160.\" 161.\" NOTICE: Also make sure to update this 162.\" 163SHA-1. 164.Pp 165How the salt is used will depend upon the algorithm for the hash. For 166best results, specify at least two characters of salt. 167.Sh RETURN VALUES 168.Pp 169.Fn crypt 170returns a pointer to the encrypted value on success, and NULL on failure. 171Note: this is not a standard behaviour, AT&T 172.Fn crypt 173will always return a pointer to a string. 174.Sh SEE ALSO 175.Xr login 1 , 176.Xr passwd 1 , 177.Xr getpass 3 , 178.Xr passwd 5 , 179.Xr shs 3 , 180.Sh BUGS 181The 182.Fn crypt 183function returns a pointer to static data, and subsequent calls to 184.Fn crypt 185will modify the same data. 186.Sh HISTORY 187A rotor-based 188.Fn crypt 189function appeared in 190.At v6 . 191The current style 192.Fn crypt 193first appeared in 194.At v7 . 195.Pp 196The DES section of the code (FreeSec 1.0) was developed outside the United 197States of America as an unencumbered replacement for the U.S.-only NetBSD 198libcrypt encryption library. 199Users should be aware that this code (and programs staticly linked with it) 200may not be exported from the U.S., although it apparently can be imported. 201.Sh AUTHORS 202Originally written by David Burren <davidb@werj.com.au>, later additions 203and changes by Brandon Gillespie, Poul-henning Kamp and Mark R V Murray. 204