HardenedBSD/secure/lib/libcrypt/crypt.3

.\" FreeSec: libcrypt for NetBSD
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.\" Copyright (c) 1994 David Burren
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.\"	$Id: crypt.3,v 1.5 1995/12/16 09:01:49 markm Exp $
.\"
.\" Manual page, using -mandoc macros
.\"
.Dd March 9, 1994
.Dt CRYPT 3
.Os "FreeSec 1.0"
.Sh NAME
.Nm crypt
.Nd DES trapdoor encryption
.Sh SYNOPSIS
.Ft char
.Fn *crypt "const char *key" "const char *setting"
.Sh DESCRIPTION
The
.Fn crypt
function performs password encryption, based on the
.Tn NBS
Data Encryption Standard (DES).
Additional code has been added to deter key search attempts.
The first argument to
.Nm crypt
is a
.Dv null Ns -terminated
string, typically a user's typed password.
The second is in one of three forms:
if it begins with an underscore (``_'') then an extended format is used
in interpreting both the the key and the setting, as outlined below.
if it begins with the string ``$1$'' then an exportable format is used.
.Ss Extended crypt:
.Pp
The
.Ar key
is divided into groups of 8 characters (the last group is null-padded)
and the low-order 7 bits of each each character (56 bits per group) are
used to form the DES key as follows:
the first group of 56 bits becomes the initial DES key.
For each additional group, the XOR of the encryption of the current DES
key with itself and the group bits becomes the next DES key.
.Pp
The setting 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 ``./0-9A-Za-z''.
This allows 24 bits for both
.Fa count
and
.Fa salt .
.Ss "Traditional" crypt:
.Pp
The first 8 bytes of the key are null-padded, and the low-order 7 bits of
each character is used to form the 56-bit
.Tn DES
key.
.Pp
The setting is a 2-character array of the ASCII-encoded salt.
Thus only 12 bits of
.Fa salt
are used.
.Fa count
is set to 25.
.Ss "FreeBSD" or "Exportable" crypt:
.Pp
If the salt begins with ``$1$'' then the freely exportable 
.Tn MD5
algorithm is used to calculate a hash value, from which the password string
is generated. The
.Tn MD5
derived routine is designed to be time-consuming like the DES based version.
.Ss Algorithm:
.Pp
The
.Fa salt
introduces disorder in the
.Tn DES
algorithm in one of 16777216 or 4096 possible ways
(ie. 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).
.Pp
The DES key is used to encrypt a 64-bit constant using
.Ar count
iterations of
.Tn DES .
The value returned is a
.Dv null Ns -terminated
string, 20 or 13 bytes (plus null) in length, consisting of the
.Ar setting
followed by the encoded 64-bit encryption.
.Pp
The function
.Fn crypt
returns a pointer to the encrypted value on success, and NULL on failure.
.Sh SEE ALSO
.Xr login 1 ,
.Xr passwd 1 ,
.Xr getpass 3 ,
.Xr passwd 5
.Sh BUGS
The
.Fn crypt
function returns a pointer to static data, and subsequent calls to
.Fn crypt
will modify the same object.
.Sh HISTORY
A rotor-based
.Fn crypt
function appeared in
.At v6 .
The current style
.Fn crypt
first appeared in
.At v7 .
.Pp
This library (FreeSec 1.0) was developed outside the United States of America
as an unencumbered replacement for the U.S.-only NetBSD libcrypt encryption
library.
Users should be aware that this code (and programs staticly linked with it)
may not be exported from the U.S., although it apparently can be imported.
.Sh AUTHOR
David Burren <davidb@werj.com.au>