fbbd9655e5
Renumber cluase 4 to 3, per what everybody else did when BSD granted them permission to remove clause 3. My insistance on keeping the same numbering for legal reasons is too pedantic, so give up on that point. Submitted by: Jan Schaumann <jschauma@stevens.edu> Pull Request: https://github.com/freebsd/freebsd/pull/96
328 lines
7.6 KiB
Groff
328 lines
7.6 KiB
Groff
.\" FreeSec: libcrypt for NetBSD
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.\"
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.\" Copyright (c) 1994 David Burren
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.\" 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 author nor the names of other 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 AUTHOR 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 AUTHOR 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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.\" $FreeBSD$
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.\"
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.Dd August 10, 2016
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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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.Nd Trapdoor 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 *salt"
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.Ft char *
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.Fn crypt_r "const char *key" "const char *salt" "struct crypt_data *data"
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.Ft const char *
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.Fn crypt_get_format "void"
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.Ft int
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.Fn crypt_set_format "const char *string"
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.Sh DESCRIPTION
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The
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.Fn crypt
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function performs password hashing with additional code added to
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deter key search attempts.
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Different algorithms can be used to
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in the hash.
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.\"
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.\" NOTICE:
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.\" If you add more algorithms, make sure to update this list
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.\" and the default used for the Traditional format, below.
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.\"
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Currently these include the
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.Tn NBS
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.Tn Data Encryption Standard (DES) ,
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.Tn MD5
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hash,
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.Tn NT-Hash
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.Pq compatible with Microsoft's NT scheme
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and
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.Tn Blowfish .
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The algorithm used will depend upon the format of the Salt
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.Po
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following
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the Modular Crypt Format
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.Pq MCF
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.Pc ,
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if
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.Tn DES
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and/or
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.Tn Blowfish
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is installed or not, and whether
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.Fn crypt_set_format
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has been called to change the default.
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.Pp
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The first argument to
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.Nm
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is the data to hash
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.Pq usually a password ,
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in a
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.Dv NUL Ns -terminated
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string.
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The second is the salt, in one of three forms:
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.Pp
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.Bl -tag -width Traditional -compact -offset indent
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.It Extended
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If it begins with an underscore
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.Pq Dq _
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then the
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.Tn DES
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Extended Format
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is used in interpreting both the key and the salt, as outlined below.
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.It Modular
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If it begins with the string
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.Dq $digit$
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then the Modular Crypt Format is used, as outlined below.
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.It Traditional
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If neither of the above is true, it assumes the Traditional Format,
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using the entire string as the salt
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.Pq or the first portion .
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.El
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.Pp
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All routines are designed to be time-consuming.
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.Ss DES Extended Format:
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The
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.Ar key
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is divided into groups of 8 characters
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.Pq the last group is NUL-padded
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and the low-order 7 bits of each character
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.Pq 56 bits per group
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are used to form the
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.Tn DES
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key as follows:
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the first group of 56 bits becomes the initial
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.Tn DES
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key.
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For each additional group, the XOR of the encryption of the current
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.Tn DES
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key with itself and the group bits becomes the next
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.Tn DES
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key.
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.Pp
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The salt is a 9-character array consisting of an underscore followed
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by 4 bytes of iteration count and 4 bytes of salt.
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These are encoded as printable characters, 6 bits per character,
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least significant character first.
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The values 0 to 63 are encoded as
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.Dq ./0-9A-Za-z .
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This allows 24 bits for both
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.Fa count
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and
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.Fa salt .
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.Pp
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The
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.Fa salt
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introduces disorder in the
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.Tn DES
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algorithm in one of 16777216 or 4096 possible ways
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.Po
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i.e., with 24 or 12 bits: 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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.Pc .
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.Pp
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The
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.Tn DES
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key is used to encrypt a 64-bit constant using
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.Ar count
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iterations of
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.Tn DES .
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The value returned is a
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.Dv NUL Ns -terminated
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string, 20 or 13 bytes
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.Pq plus NUL
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in length, consisting of the
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.Ar salt
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followed by the encoded 64-bit encryption.
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.Ss Modular crypt:
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If the salt begins with the string
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.Fa $digit$
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then the Modular Crypt Format is used.
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The
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.Fa digit
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represents which algorithm is used in encryption.
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Following the token is
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the actual salt to use in the encryption.
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The maximum length of the salt used depends upon the module.
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The salt must be terminated with the end of the string character
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.Pq NUL
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or a dollar sign.
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Any characters after the dollar sign are ignored.
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.Pp
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Currently supported algorithms are:
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.Pp
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.Bl -enum -compact -offset indent
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.It
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MD5
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.It
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Blowfish
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.It
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NT-Hash
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.It
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(unused)
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.It
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SHA-256
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.It
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SHA-512
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.El
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.Pp
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Other crypt formats may be easily added.
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An example salt would be:
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.Bl -tag -width 6n -offset indent
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.It Cm "$4$thesalt$rest"
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.El
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.Ss Traditional crypt:
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The algorithm used will depend upon whether
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.Fn crypt_set_format
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has been called and whether a global default format has been specified.
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Unless a global default has been specified or
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.Fn crypt_set_format
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has set the format to something else, the built-in default format is
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used.
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This is currently
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.\"
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.\" NOTICE: Also make sure to update this
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.\"
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DES
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if it is available, or MD5 if not.
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.Pp
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How the salt is used will depend upon the algorithm for the hash.
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For
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best results, specify at least eight characters of salt.
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.Pp
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The
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.Fn crypt_get_format
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function returns a constant string that represents the name of the
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algorithm currently used.
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Valid values are
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.\"
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.\" NOTICE: Also make sure to update this, too, as well
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.\"
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.Ql des ,
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.Ql blf ,
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.Ql md5 ,
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.Ql sha256 ,
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.Ql sha512
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and
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.Ql nth .
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.Pp
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The
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.Fn crypt_set_format
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function sets the default encoding format according to the supplied
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.Fa string .
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.Pp
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The
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.Fn crypt_r
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function behaves identically to
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.Fn crypt ,
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except that the resulting string is stored in
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.Fa data ,
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making it thread-safe.
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.Sh RETURN VALUES
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The
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.Fn crypt
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and
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.Fn crypt_r
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functions return a pointer to the encrypted value on success, and NULL on
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failure.
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Note: this is not a standard behaviour, AT&T
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.Fn crypt
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will always return a pointer to a string.
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.Pp
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The
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.Fn crypt_set_format
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function will return 1 if the supplied encoding format was valid.
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Otherwise, a value of 0 is returned.
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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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.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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.Pp
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The
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.Tn DES
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section of the code (FreeSec 1.0) was developed outside the United
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States of America as an unencumbered replacement for the U.S.-only
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.Nx
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libcrypt encryption library.
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.Pp
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The
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.Fn crypt_r
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function was added in
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.Fx 12.0 .
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.Sh AUTHORS
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.An -nosplit
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Originally written by
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.An David Burren Aq Mt davidb@werj.com.au ,
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later additions and changes by
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.An Poul-Henning Kamp ,
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.An Mark R V Murray ,
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.An Michael Bretterklieber ,
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.An Kris Kennaway ,
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.An Brian Feldman ,
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.An Paul Herman
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and
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.An Niels Provos .
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.Sh BUGS
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The
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.Fn crypt
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function returns a pointer to static data, and subsequent calls to
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.Fn crypt
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will modify the same data.
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Likewise,
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.Fn crypt_set_format
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modifies static data.
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.Pp
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The NT-hash scheme does not use a salt,
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and is not hard
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for a competent attacker
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to break.
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Its use is not recommended.
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