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Makefile.depend
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crypt-md5.c
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crypt.3
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crypt.c
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crypt.h
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tests
Editing: crypt.3
.\" FreeSec: libcrypt for NetBSD .\" .\" Copyright (c) 1994 David Burren .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. Neither the name of the author nor the names of other contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" $FreeBSD$ .\" .Dd May 26, 2019 .Dt CRYPT 3 .Os .Sh NAME .Nm crypt .Nd Trapdoor encryption .Sh LIBRARY .Lb libcrypt .Sh SYNOPSIS .In unistd.h .Ft char * .Fn crypt "const char *key" "const char *salt" .Ft char * .Fn crypt_r "const char *key" "const char *salt" "struct crypt_data *data" .Ft const char * .Fn crypt_get_format "void" .Ft int .Fn crypt_set_format "const char *string" .Sh DESCRIPTION The .Fn crypt function performs password hashing with additional code added to deter key search attempts. Different algorithms can be used to in the hash. .\" .\" NOTICE: .\" If you add more algorithms, make sure to update this list .\" and the default used for the Traditional format, below. .\" Currently these include the .Tn NBS .Tn Data Encryption Standard (DES) , .Tn MD5 hash, .Tn NT-Hash .Pq compatible with Microsoft's NT scheme and .Tn Blowfish . The algorithm used will depend upon the format of the Salt .Po following the Modular Crypt Format .Pq MCF .Pc , if .Tn DES and/or .Tn Blowfish is installed or not, and whether .Fn crypt_set_format has been called to change the default. .Pp The first argument to .Nm is the data to hash .Pq usually a password , in a .Dv NUL Ns -terminated string. The second is the salt, in one of three forms: .Pp .Bl -tag -width Traditional -compact -offset indent .It Extended If it begins with an underscore .Pq Dq _ then the .Tn DES Extended Format is used in interpreting both the key and the salt, as outlined below. .It Modular If it begins with the string .Dq $digit$ then the Modular Crypt Format is used, as outlined below. .It Traditional If neither of the above is true, it assumes the Traditional Format, using the entire string as the salt .Pq or the first portion . .El .Pp All routines are designed to be time-consuming. .Ss DES Extended Format: The .Ar key is divided into groups of 8 characters .Pq the last group is NUL-padded and the low-order 7 bits of each character .Pq 56 bits per group are used to form the .Tn DES key as follows: the first group of 56 bits becomes the initial .Tn DES key. For each additional group, the XOR of the encryption of the current .Tn DES key with itself and the group bits becomes the next .Tn DES key. .Pp The salt is a 9-character array consisting of an underscore followed by 4 bytes of iteration count and 4 bytes of salt. These are encoded as printable characters, 6 bits per character, least significant character first. The values 0 to 63 are encoded as .Dq ./0-9A-Za-z . This allows 24 bits for both .Fa count and .Fa salt . .Pp The .Fa salt introduces disorder in the .Tn DES algorithm in one of 16777216 or 4096 possible ways .Po i.e., with 24 or 12 bits: if bit .Em i of the .Ar salt is set, then bits .Em i and .Em i+24 are swapped in the .Tn DES E-box output .Pc . .Pp The .Tn DES key is used to encrypt a 64-bit constant using .Ar count iterations of .Tn DES . The value returned is a .Dv NUL Ns -terminated string, 20 or 13 bytes .Pq plus NUL in length, consisting of the .Ar salt followed by the encoded 64-bit encryption. .Ss Modular crypt: If the salt begins with the string .Fa $digit$ then the Modular Crypt Format is used. The .Fa digit represents which algorithm is used in encryption. Following the token is the actual salt to use in the encryption. The maximum length of the salt used depends upon the module. The salt must be terminated with the end of the string character .Pq NUL or a dollar sign. Any characters after the dollar sign are ignored. .Pp Currently supported algorithms are: .Pp .Bl -enum -compact -offset indent .It MD5 .It Blowfish .It NT-Hash .It (unused) .It SHA-256 .It SHA-512 .El .Pp Other crypt formats may be easily added. An example salt would be: .Bl -tag -width 6n -offset indent .It Cm "$4$thesalt$rest" .El .Ss Traditional crypt: The algorithm used will depend upon whether .Fn crypt_set_format has been called and whether a global default format has been specified. Unless a global default has been specified or .Fn crypt_set_format has set the format to something else, the built-in default format is used. This is currently .\" .\" NOTICE: Also make sure to update this .\" DES if it is available, or SHA-512 if not. .Pp How the salt is used will depend upon the algorithm for the hash. For best results, specify at least eight characters of salt. .Pp The .Fn crypt_get_format function returns a constant string that represents the name of the algorithm currently used. Valid values are .\" .\" NOTICE: Also make sure to update this, too, as well .\" .Ql des , .Ql blf , .Ql md5 , .Ql sha256 , .Ql sha512 and .Ql nth . .Pp The .Fn crypt_set_format function sets the default encoding format according to the supplied .Fa string . .Pp The .Fn crypt_r function behaves identically to .Fn crypt , except that the resulting string is stored in .Fa data , making it thread-safe. .Sh RETURN VALUES The .Fn crypt and .Fn crypt_r functions return a pointer to the encrypted value on success, and NULL on failure. Note: this is not a standard behaviour, AT&T .Fn crypt will always return a pointer to a string. .Pp The .Fn crypt_set_format function will return 1 if the supplied encoding format was valid. Otherwise, a value of 0 is returned. .Sh SEE ALSO .Xr login 1 , .Xr passwd 1 , .Xr getpass 3 , .Xr passwd 5 .Sh HISTORY A rotor-based .Fn crypt function appeared in .At v6 . The current style .Fn crypt first appeared in .At v7 . .Pp The .Tn DES section of the code (FreeSec 1.0) was developed outside the United States of America as an unencumbered replacement for the U.S.-only .Nx libcrypt encryption library. .Pp The .Fn crypt_r function was added in .Fx 12.0 . .Sh AUTHORS .An -nosplit Originally written by .An David Burren Aq Mt davidb@werj.com.au , later additions and changes by .An Poul-Henning Kamp , .An Mark R V Murray , .An Michael Bretterklieber , .An Kris Kennaway , .An Brian Feldman , .An Paul Herman and .An Niels Provos . .Sh BUGS The .Fn crypt function returns a pointer to static data, and subsequent calls to .Fn crypt will modify the same data. Likewise, .Fn crypt_set_format modifies static data. .Pp The NT-hash scheme does not use a salt, and is not hard for a competent attacker to break. Its use is not recommended.
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