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.\" 32.\" Manual page, using -mandoc macros 33.\" 34.Dd January 19, 1997 35.Dt CRYPT 3 36.Os 37.Sh NAME 38.Nm crypt 39.Nd Trapdoor encryption 40.Sh LIBRARY 41.Lb libcrypt 42.Sh SYNOPSIS 43.In 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) , 64.Tn MD5 65and 66.Tn Blowfish . 67The algorithm used will depend upon the format of the Salt (following 68the Modular Crypt Format (MCF)), if 69.Tn DES 70and/or 71.Tn Blowfish 72is installed or not, and whether 73.Fn crypt_set_format 74has been called to change the default. 75.Pp 76The first argument to 77.Nm 78is the data to hash (usually a password), in a 79.Dv null Ns -terminated 80string. 81The second is the salt, in one of three forms: 82.Pp 83.Bl -tag -width Traditional -compact -offset indent 84.It Extended 85If it begins with an underscore 86.Pq Dq _ 87then the 88.Tn DES 89Extended Format 90is used in interpreting both the key and the salt, as outlined below. 91.It Modular 92If it begins with the string 93.Dq $digit$ 94then the Modular Crypt Format is used, as outlined below. 95.It Traditional 96If neither of the above is true, it assumes the Traditional Format, 97using the entire string as the salt (or the first portion). 98.El 99.Pp 100All routines are designed to be time-consuming. A brief test on a 101.Tn Pentium 102166/MMX shows the 103.Tn DES 104crypt to do approximately 2640 crypts 105a CPU second and MD5 to do about 62 crypts a CPU second. 106.Ss DES Extended Format: 107.Pp 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: 163.Pp 164If the salt begins with the string 165.Fa $digit$ 166then the Modular Crypt Format is used. The 167.Fa digit 168represents which algorithm is used in encryption. Following the token is 169the actual salt to use in the encryption. The length of the salt is limited 170to 8 characters--because the length of the returned output is also limited 171(_PASSWORD_LEN). The salt must be terminated with the end of the string 172(NULL) or a dollar sign. Any characters after the dollar sign are ignored. 173.Pp 174Currently supported algorithms are: 175.Pp 176.Bl -enum -compact -offset indent 177.It 178MD5 179.It 180Blowfish 181.El 182.Pp 183Other crypt formats may be easily added. An example salt would be: 184.Bl -tag -offset indent 185.It Cm "$3$thesalt$rest" 186.El 187.Pp 188.Ss "Traditional" crypt: 189.Pp 190The algorithm used will depend upon whether 191.Fn crypt_set_format 192has been called and whether a global default format has been specified. 193Unless a global default has been specified or 194.Fn crypt_set_format 195has set the format to something else, the built-in default format is 196used. 197This is currently 198.\" 199.\" NOTICE: Also make sure to update this 200.\" 201DES 202if it is available, or MD5 if not. 203.Pp 204How the salt is used will depend upon the algorithm for the hash. For 205best results, specify at least two characters of salt. 206.Pp 207The 208.Fn crypt_get_format 209function returns a constant string that represents the name of the 210algorithm currently used. 211Valid values are 212.\" 213.\" NOTICE: Also make sure to update this, too, as well 214.\" 215.Ql des , 216.Ql blf 217and 218.Ql md5 . 219.Pp 220The 221.Fn crypt_set_format 222function sets the default encoding format according to the supplied 223.Fa string . 224.Pp 225The global default format can be set using the 226.Pa /etc/auth.conf 227file using the 228.Va crypt_default 229property. 230.Sh RETURN VALUES 231.Fn crypt 232returns a pointer to the encrypted value on success, and NULL on failure. 233Note: this is not a standard behaviour, AT&T 234.Fn crypt 235will always return a pointer to a string. 236.Pp 237.Fn crypt_set_format 238will return 1 if the supplied encoding format was valid. 239Otherwise, a value of 0 is returned. 240.Sh SEE ALSO 241.Xr login 1 , 242.Xr passwd 1 , 243.Xr auth_getval 3 , 244.Xr cipher 3 , 245.Xr getpass 3 , 246.Xr auth.conf 5 , 247.Xr passwd 5 248.Sh BUGS 249The 250.Fn crypt 251function returns a pointer to static data, and subsequent calls to 252.Fn crypt 253will modify the same data. Likewise, 254.Fn crypt_set_format 255modifies static data. 256.Sh HISTORY 257A rotor-based 258.Fn crypt 259function appeared in 260.At v6 . 261The current style 262.Fn crypt 263first appeared in 264.At v7 . 265.Pp 266The 267.Tn DES 268section of the code (FreeSec 1.0) was developed outside the United 269States of America as an unencumbered replacement for the U.S.-only 270.Nx 271libcrypt encryption library. 272.Sh AUTHORS 273.An -nosplit 274Originally written by 275.An David Burren Aq davidb@werj.com.au , 276later additions and changes by 277.An Poul-Henning Kamp , 278.An Mark R V Murray , 279.An Kris Kennaway , 280.An Brian Feldman , 281.An Paul Herman 282and 283.An Niels Provos . 284