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 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 65hash, 66.Tn NT-Hash 67(compatible with Microsoft's NT scheme) 68and 69.Tn Blowfish . 70The algorithm used will depend upon the format of the Salt (following 71the Modular Crypt Format (MCF)), if 72.Tn DES 73and/or 74.Tn Blowfish 75is installed or not, and whether 76.Fn crypt_set_format 77has been called to change the default. 78.Pp 79The first argument to 80.Nm 81is the data to hash (usually a password), in a 82.Dv null Ns -terminated 83string. 84The second is the salt, in one of three forms: 85.Pp 86.Bl -tag -width Traditional -compact -offset indent 87.It Extended 88If it begins with an underscore 89.Pq Dq _ 90then the 91.Tn DES 92Extended Format 93is used in interpreting both the key and the salt, as outlined below. 94.It Modular 95If it begins with the string 96.Dq $digit$ 97then the Modular Crypt Format is used, as outlined below. 98.It Traditional 99If neither of the above is true, it assumes the Traditional Format, 100using the entire string as the salt (or the first portion). 101.El 102.Pp 103All routines are designed to be time-consuming. A brief test on a 104.Tn Pentium 105166/MMX shows the 106.Tn DES 107crypt to do approximately 2640 crypts 108a CPU second and MD5 to do about 62 crypts a CPU second. 109.Ss DES Extended Format: 110.Pp 111The 112.Ar key 113is divided into groups of 8 characters (the last group is null-padded) 114and the low-order 7 bits of each character (56 bits per group) are 115used to form the 116.Tn DES 117key as follows: 118the first group of 56 bits becomes the initial 119.Tn DES 120key. 121For each additional group, the XOR of the encryption of the current 122.Tn DES 123key with itself and the group bits becomes the next 124.Tn DES 125key. 126.Pp 127The salt is a 9-character array consisting of an underscore followed 128by 4 bytes of iteration count and 4 bytes of salt. 129These are encoded as printable characters, 6 bits per character, 130least significant character first. 131The values 0 to 63 are encoded as ``./0-9A-Za-z''. 132This allows 24 bits for both 133.Fa count 134and 135.Fa salt . 136.Pp 137The 138.Fa salt 139introduces disorder in the 140.Tn DES 141algorithm in one of 16777216 or 4096 possible ways 142(ie. with 24 or 12 bits: if bit 143.Em i 144of the 145.Ar salt 146is set, then bits 147.Em i 148and 149.Em i+24 150are swapped in the 151.Tn DES 152E-box output). 153.Pp 154The 155.Tn DES 156key is used to encrypt a 64-bit constant using 157.Ar count 158iterations of 159.Tn DES . 160The value returned is a 161.Dv null Ns -terminated 162string, 20 or 13 bytes (plus null) in length, consisting of the 163.Ar salt 164followed by the encoded 64-bit encryption. 165.Ss "Modular" crypt: 166.Pp 167If the salt begins with the string 168.Fa $digit$ 169then the Modular Crypt Format is used. The 170.Fa digit 171represents which algorithm is used in encryption. Following the token is 172the actual salt to use in the encryption. The length of the salt is limited 173to 8 characters--because the length of the returned output is also limited 174(_PASSWORD_LEN). The salt must be terminated with the end of the string 175(NULL) or a dollar sign. Any characters after the dollar sign are ignored. 176.Pp 177Currently supported algorithms are: 178.Pp 179.Bl -enum -compact -offset indent 180.It 181MD5 182.It 183Blowfish 184.It 185NT-Hash 186.El 187.Pp 188Other crypt formats may be easily added. An example salt would be: 189.Bl -tag -offset indent 190.It Cm "$4$thesalt$rest" 191.El 192.Pp 193.Ss "Traditional" crypt: 194.Pp 195The algorithm used will depend upon whether 196.Fn crypt_set_format 197has been called and whether a global default format has been specified. 198Unless a global default has been specified or 199.Fn crypt_set_format 200has set the format to something else, the built-in default format is 201used. 202This is currently 203.\" 204.\" NOTICE: Also make sure to update this 205.\" 206DES 207if it is available, or MD5 if not. 208.Pp 209How the salt is used will depend upon the algorithm for the hash. For 210best results, specify at least two characters of salt. 211.Pp 212The 213.Fn crypt_get_format 214function returns a constant string that represents the name of the 215algorithm currently used. 216Valid values are 217.\" 218.\" NOTICE: Also make sure to update this, too, as well 219.\" 220.Ql des , 221.Ql blf , 222.Ql md5 223and 224.Ql nth . 225.Pp 226The 227.Fn crypt_set_format 228function sets the default encoding format according to the supplied 229.Fa string . 230.Pp 231The global default format can be set using the 232.Pa /etc/auth.conf 233file using the 234.Va crypt_default 235property. 236.Sh RETURN VALUES 237The 238.Fn crypt 239function returns a pointer to the encrypted value on success, and NULL on 240failure. 241Note: this is not a standard behaviour, AT&T 242.Fn crypt 243will always return a pointer to a string. 244.Pp 245The 246.Fn crypt_set_format 247function will return 1 if the supplied encoding format was valid. 248Otherwise, a value of 0 is returned. 249.Sh SEE ALSO 250.Xr login 1 , 251.Xr passwd 1 , 252.Xr auth_getval 3 , 253.Xr cipher 3 , 254.Xr getpass 3 , 255.Xr auth.conf 5 , 256.Xr passwd 5 257.Sh BUGS 258The 259.Fn crypt 260function returns a pointer to static data, and subsequent calls to 261.Fn crypt 262will modify the same data. Likewise, 263.Fn crypt_set_format 264modifies static data. 265.Pp 266The NT-hash scheme does not use a salt, 267and is not hard 268for a competent attacker 269to break. 270Its use is not recommended. 271.Sh HISTORY 272A rotor-based 273.Fn crypt 274function appeared in 275.At v6 . 276The current style 277.Fn crypt 278first appeared in 279.At v7 . 280.Pp 281The 282.Tn DES 283section of the code (FreeSec 1.0) was developed outside the United 284States of America as an unencumbered replacement for the U.S.-only 285.Nx 286libcrypt encryption library. 287.Sh AUTHORS 288.An -nosplit 289Originally written by 290.An David Burren Aq davidb@werj.com.au , 291later additions and changes by 292.An Poul-Henning Kamp , 293.An Mark R V Murray , 294.An Michael Bretterklieber , 295.An Kris Kennaway , 296.An Brian Feldman , 297.An Paul Herman 298and 299.An Niels Provos . 300