298 lines
6.9 KiB
Groff
298 lines
6.9 KiB
Groff
.\" Copyright (c) 1989, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)crypt.3 8.2 (Berkeley) 12/11/93
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.\"
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.Dd December 11, 1993
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.Dt CRYPT 3
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.Os
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.Sh NAME
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.Nm crypt ,
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.Nm setkey ,
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.Nm encrypt ,
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.Nm des_setkey ,
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.Nm des_cipher
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.Nd DES encryption
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.Sh SYNOPSIS
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.Ft char
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.Fn *crypt "const char *key" "const char *setting"
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.Ft int
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.Fn setkey "char *key"
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.Ft int
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.Fn encrypt "char *block" "int flag"
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.Ft int
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.Fn des_setkey "const char *key"
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.Ft int
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.Fn des_cipher "const char *in" "char *out" "long salt" "int count"
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.Sh DESCRIPTION
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The
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.Xr crypt
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function
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performs password encryption.
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It is derived from the
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.Tn NBS
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Data Encryption Standard.
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Additional code has been added to deter
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key search attempts.
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The first argument to
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.Nm crypt
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is
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a
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.Dv NUL Ns -terminated
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string (normally a password typed by a user).
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The second is a character array, 9 bytes in length, consisting of an
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underscore (``_'') followed by 4 bytes of iteration count and 4 bytes
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of salt.
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Both the iteration
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.Fa count
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and the
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.Fa salt
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are encoded with 6 bits per character, least significant bits first.
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The values 0 to 63 are encoded by the characters ``./0-9A-Za-z'',
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respectively.
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.Pp
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The
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.Fa salt
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is used to induce disorder in to the
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.Tn DES
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algorithm
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in one of 16777216
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possible ways
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(specifically, if bit
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.Em i
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of the
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.Ar salt
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is set then bits
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.Em i
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and
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.Em i+24
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are swapped in the
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.Tn DES
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``E'' box output).
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The
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.Ar key
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is divided into groups of 8 characters (a short final group is null-padded)
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and the low-order 7 bits of each character (56 bits per group) are
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used to form the DES key as follows: the first group of 56 bits becomes the
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initial DES key.
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For each additional group, the XOR of the group bits and the encryption of
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the DES key with itself becomes the next DES key.
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Then the final DES key is used to perform
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.Ar count
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cumulative encryptions of a 64-bit constant.
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The value returned is a
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.Dv NUL Ns -terminated
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string, 20 bytes in length, consisting
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of the
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.Ar setting
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followed by the encoded 64-bit encryption.
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.Pp
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For compatibility with historical versions of
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.Xr crypt 3 ,
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the
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.Ar setting
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may consist of 2 bytes of salt, encoded as above, in which case an
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iteration
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.Ar count
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of 25 is used, fewer perturbations of
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.Tn DES
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are available, at most 8
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characters of
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.Ar key
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are used, and the returned value is a
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.Dv NUL Ns -terminated
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string 13 bytes in length.
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.Pp
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The
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functions,
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.Fn encrypt ,
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.Fn setkey ,
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.Fn des_setkey
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and
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.Fn des_cipher
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allow limited access to the
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.Tn DES
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algorithm itself.
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The
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.Ar key
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argument to
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.Fn setkey
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is a 64 character array of
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binary values (numeric 0 or 1).
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A 56-bit key is derived from this array by dividing the array
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into groups of 8 and ignoring the last bit in each group.
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.Pp
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The
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.Fn encrypt
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argument
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.Fa block
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is also a 64 character array of
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binary values.
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If the value of
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.Fa flag
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is 0,
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the argument
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.Fa block
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is encrypted, otherwise it
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is decrypted.
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The encryption or decryption is returned in the original
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array
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.Fa block
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after using the
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key specified
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by
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.Fn setkey
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to process it.
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.Pp
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The
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.Fn des_setkey
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and
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.Fn des_cipher
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functions are faster but less portable than
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.Fn setkey
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and
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.Fn encrypt .
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The argument to
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.Fn des_setkey
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is a character array of length 8.
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The
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.Em least
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significant bit in each character is ignored and the next 7 bits of each
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character are concatenated to yield a 56-bit key.
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The function
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.Fn des_cipher
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encrypts (or decrypts if
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.Fa count
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is negative) the 64-bits stored in the 8 characters at
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.Fa in
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using
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.Xr abs 3
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of
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.Fa count
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iterations of
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.Tn DES
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and stores the 64-bit result in the 8 characters at
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.Fa out .
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The
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.Fa salt
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specifies perturbations to
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.Tn DES
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as described above.
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.Pp
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The function
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.Fn crypt
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returns a pointer to the encrypted value on success and NULL on failure.
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The functions
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.Fn setkey ,
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.Fn encrypt ,
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.Fn des_setkey ,
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and
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.Fn des_cipher
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return 0 on success and 1 on failure.
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Historically, the functions
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.Fn setkey
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and
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.Fn encrypt
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did not return any value.
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They have been provided return values primarily to distinguish
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implementations where hardware support is provided but not
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available or where the DES encryption is not available due to the
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usual political silliness.
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.Pp
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Use of
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.Fn crypt
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requires linking with the
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.Nm libcrypt
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library. The
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.Fn setkey ,
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.Fn encrypt ,
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.Fn des_setkey
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and
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.Fn des_cipher
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can be found in the
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.Nm libcipher
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library (the standard C library,
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.Nm libc ,
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only contains stubs to these routines).
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.Sh SEE ALSO
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.Xr login 1 ,
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.Xr passwd 1 ,
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.Xr getpass 3 ,
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.Xr passwd 5
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.sp
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.Rs
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.%T "Mathematical Cryptology for Computer Scientists and Mathematicians"
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.%A Wayne Patterson
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.%D 1987
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.%N ISBN 0-8476-7438-X
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.Re
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.Rs
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.%T "Password Security: A Case History"
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.%A R. Morris
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.%A Ken Thompson
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.%J "Communications of the ACM"
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.%V vol. 22
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.%P pp. 594-597
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.%D Nov. 1979
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.Re
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.Rs
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.%T "DES will be Totally Insecure within Ten Years"
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.%A M.E. Hellman
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.%J "IEEE Spectrum"
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.%V vol. 16
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.%P pp. 32-39
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.%D July 1979
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.Re
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.Sh HISTORY
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A rotor-based
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.Fn crypt
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function appeared in
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.At v6 .
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The current style
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.Fn crypt
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first appeared in
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.At v7 .
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.Sh BUGS
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Dropping the
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.Em least
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significant bit in each character of the argument to
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.Fn des_setkey
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is ridiculous.
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.Pp
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The
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.Fn crypt
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function leaves its result in an internal static object and returns
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a pointer to that object.
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Subsequent calls to
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.Fn crypt
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will modify the same object.
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