407 lines
9.6 KiB
Groff
407 lines
9.6 KiB
Groff
.\" $NetBSD: crypt.3,v 1.27 2012/03/23 18:08:35 njoly Exp $
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.\"
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.\" 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. 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 January 1, 2012
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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 password encryption
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.Sh LIBRARY
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.Lb libcrypt
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.Sh SYNOPSIS
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.In unistd.h
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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 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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.In stdlib.h
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.Ft int
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.Fn setkey "const char *key"
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.Sh DESCRIPTION
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The
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.Fn crypt
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function
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performs password encryption.
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The encryption scheme used by
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.Fn crypt
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is dependent upon the contents of the
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.Dv NUL Ns -terminated
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string
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.Ar setting .
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If it begins
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with a string character
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.Pq Ql $
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and a number then a different algorithm is used depending on the number.
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At the moment a
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.Ql $1
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chooses MD5 hashing and a
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.Ql $2
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chooses Blowfish hashing; see below for more information.
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If
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.Ar setting
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begins with the ``_'' character, DES encryption with a user specified number
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of perturbations is selected.
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If
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.Ar setting
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begins with any other character, DES encryption with a fixed number
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of perturbations is selected.
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.Ss DES encryption
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The DES encryption scheme 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 key search attempts and to use
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stronger hashing algorithms.
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In the DES case, the second argument to
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.Fn crypt
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is a character array, 9 bytes in length, consisting of an underscore (``_'')
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followed by 4 bytes of iteration count and 4 bytes 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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.Fn crypt ,
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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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.Ss MD5 encryption
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For the
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.Tn MD5
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encryption scheme, the version number (in this case ``1''),
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.Fa salt
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and the hashed password are separated
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by the ``$'' character.
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A valid password looks like this:
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.Pp
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``$1$2qGr5PPQ$eT08WBFev3RPLNChixg0H.''.
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.Pp
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The entire password string is passed as
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.Fa setting
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for interpretation.
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.Ss "Blowfish" crypt
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The
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.Tn Blowfish
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version of
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.Fn crypt
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has 128 bits of
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.Fa salt
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in order to make building dictionaries of common passwords space consuming.
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The initial state of the
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.Tn Blowfish
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cipher is expanded using the
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.Fa salt
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and the
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.Fa password
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repeating the process a variable number of rounds, which is encoded in
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the password string.
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The maximum password length is 72.
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The final Blowfish password entry is created by encrypting the string
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.Pp
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.Dq OrpheanBeholderScryDoubt
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.Pp
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with the
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.Tn Blowfish
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state 64 times.
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.Pp
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The version number, the logarithm of the number of rounds and
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the concatenation of salt and hashed password are separated by the
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.Ql $
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character.
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An encoded
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.Sq 8
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would specify 256 rounds.
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A valid Blowfish password looks like this:
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.Pp
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.Dq $2a$12$eIAq8PR8sIUnJ1HaohxX2O9x9Qlm2vK97LJ5dsXdmB.eXF42qjchC .
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.Pp
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The whole Blowfish password string is passed as
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.Fa setting
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for interpretation.
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.Sh RETURN VALUES
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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.
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.Pp
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The behavior of
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.Fn crypt
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on errors isn't well standardized.
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Some implementations simply can't fail (unless the process dies, in which
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case they obviously can't return), others return
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.Dv NULL
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or a fixed string.
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Most implementations don't set
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.Va errno ,
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but some do.
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.St -susv2
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specifies
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only returning
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.Dv NULL
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and setting
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.Va errno
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as a valid behavior, and defines
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only one possible error
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.Er ( ENOSYS ,
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.Dq "The functionality is not supported on this implementation." )
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Unfortunately, most existing applications aren't prepared to handle
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.Dv NULL
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returns from
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.Fn crypt .
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The description below corresponds to this implementation of
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.Fn crypt
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only.
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The behavior may change to match standards, other implementations or existing
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applications.
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.Pp
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.Fn crypt
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may only fail (and return) when passed an invalid or unsupported
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.Fa setting ,
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in which case it returns a pointer to a magic string that is shorter than 13
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characters and is guaranteed to differ from
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.Fa setting .
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This behavior is safe for older applications which assume that
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.Fn crypt
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can't fail, when both setting new passwords and authenticating against
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existing password hashes.
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.Pp
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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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.Sh SEE ALSO
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.Xr login 1 ,
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.Xr passwd 1 ,
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.Xr pwhash 1 ,
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.Xr getpass 3 ,
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.Xr md5 3 ,
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.Xr passwd 5 ,
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.Xr passwd.conf 5
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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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.Pp
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Before
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.Nx 6.0
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.Fn crypt
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returned either
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.Dv NULL
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or
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.Dv \&:
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on error.
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