bionic (3) Authen::Passphrase::DESCrypt.3pm.gz
NAME
Authen::Passphrase::DESCrypt - passphrases using the DES-based Unix crypt()
SYNOPSIS
use Authen::Passphrase::DESCrypt;
$ppr = Authen::Passphrase::DESCrypt->new(
salt_base64 => "my",
hash_base64 => "TYK.j.88/9s");
$ppr = Authen::Passphrase::DESCrypt->new(
salt_random => 12,
passphrase => "passphrase");
$ppr = Authen::Passphrase::DESCrypt
->from_crypt('myTYK.j.88/9s');
$ppr = Authen::Passphrase::DESCrypt->new(
fold => 1,
initial => "xyzzy!!!",
nrounds => 500,
salt_base64 => "quux",
hash_base64 => "QCKcHlgVsRY");
$fold = $ppr->fold;
$initial = $ppr->initial;
$initial_base64 = $ppr->initial_base64;
$nrounds = $ppr->nrounds;
$nrounds_base64 = $ppr->nrounds_base64_4;
$salt = $ppr->salt;
$salt_base64 = $ppr->salt_base64_2;
$salt_base64 = $ppr->salt_base64_4;
$hash = $ppr->hash;
$hash_base64 = $ppr->hash_base64;
if($ppr->match($passphrase)) { ...
$passwd = $ppr->as_crypt;
$userPassword = $ppr->as_rfc2307;
DESCRIPTION
An object of this class encapsulates a passphrase hashed using some form of the DES-based Unix crypt()
hash function. This is a subclass of Authen::Passphrase, and this document assumes that the reader is
familiar with the documentation for that class.
The crypt() function in a modern Unix actually supports several different passphrase schemes. That is
not what this class is about. This class is concerned only with one family of schemes, variants of the
DES-based scheme that crypt() originally implemented, which confusingly is usually referred to merely as
"crypt()". To handle the whole range of passphrase schemes supported by the modern crypt(), see the
from_crypt constructor and the as_crypt method in Authen::Passphrase.
Warning: this password scheme is weak by modern standards, and in any case does not support a large
password space. Cracking crypt()ed passwords has been a routine activity since the early 1990s. This
scheme is supported for compatibility reasons only, and should not be used except when compatibility is
required. Do not use this in the design of any new system or for new passwords in any system that
supports better passphrase schemes.
The traditional DES-based Unix crypt() password scheme
The traditional Unix crypt() password scheme is based on the DES block encryption algorithm. Using the
password as a 56-bit key, it passes a 64-bit data block, initialised to zero, through the encryption
function 25 times, and the hash is the 64-bit output of this process. A 12-bit salt is used to tweak the
encryption algorithm.
The 56-bit key is extracted from the password in a very poor way. Only the first eight bytes of the
password are used, and any remainder is ignored. This makes it impossible to use a passphrase, rather
than a password, hence the terminology in this section. Of the eight bytes used, the top bit is also
ignored; this function hails from the days of pure ASCII.
A password hash of this scheme is conventionally represented in ASCII as a 13-character string using a
base 64 encoding. The base 64 digits are ".", "/", "0" to "9", "A" to "Z", "a" to "z" (in ASCII order).
The first two characters give the 12-bit salt. The remaining eleven characters give the 64-bit hash.
Because the base 64 encoding can represent 66 bits in eleven digits, more than the 64 required, the last
character of the string can only take sixteen of the base 64 digit values.
Variant DES-based Unix crypt() passphrase schemes
To make password cracking more difficult, historically some Unix sites modified the crypt() function to
be incompatible with the standard one. This was easily achieved by initialising the data block to
something other than the standard all-bits-zero. Another variation used was to increase the number of
encryption rounds, which makes cracking take longer in addition to being non-standard. Password hashes
on such a system looked normal but were not interoperable with standard crypt() implementations. To
interpret them properly it is necessary to know the modified parameters.
BSDi standardised an extended DES-based scheme. The salt is extended to 24 bits, and the number of
encryption rounds is variable. Passphrases longer than 8 characters are handled by an additional step
that folds (hashes) them down to 8 characters, rather than just throwing away the characters after the
eighth. Passphrase hashes in this scheme are conventionally represented in ASCII as a "_" followed by 19
characters of base 64. The first four base 64 digits give the number of encryption rounds, the next four
give the salt, and the remaining eleven give the hash.
CONSTRUCTORS
Authen::Passphrase::DESCrypt->new(ATTR => VALUE, ...)
Generates a new passphrase recogniser object using the generalised DES-based crypt() algorithm. The
following attributes may be given:
fold
Truth value indicating whether the BSDi passphrase folding scheme should be used for long
passphrases. Default false, for compatibility with the original DES-based scheme.
initial
The initial data block to encrypt, as a string of exactly eight bytes. Default all bits zero,
for compatibility with the original DES-based scheme.
initial_base64
The initial data block to encrypt, as a string of eleven base 64 digits.
nrounds
The number of encryption rounds to use, as a Perl integer. Default 25, for compatibility with
the original DES-based scheme.
nrounds_base64
The number of encryption rounds to use, as a string of four base 64 digits.
salt
The salt, as an integer in the range [0, 16777216).
salt_base64
The salt, as a string of two or four base 64 digits.
salt_random
Causes salt to be generated randomly. The value given for this attribute must be either 12 or
24, giving the number of bits of salt to generate. The source of randomness may be controlled by
the facility described in Data::Entropy.
hash
The hash (output of encryption), as a string of exactly eight bytes.
hash_base64
The hash, as a string of eleven base 64 digits.
passphrase
A passphrase that will be accepted.
The salt must be given, and either the hash or the passphrase. The other parameters default to those
used in the original DES-based crypt().
Authen::Passphrase::DESCrypt->from_crypt(PASSWD)
Generates a new passphrase recogniser object using the DES-based crypt() algorithm, from a crypt
string. Two forms of crypt string are supported.
The first form of crypt string must consist of 13 base 64 digits. The first two give the salt, and
the next eleven give the hash. Long passphrases are not folded, the initial block is all bits zero,
and 25 encryption rounds are performed.
The second form of crypt string must consist of an "_" followed by 19 base 64 digits. The first four
give the number of encryption rounds, the next four give the salt, and the next eleven give the hash.
Long passphrases are folded, and the initial block is all bits zero.
Authen::Passphrase::DESCrypt->from_rfc2307(USERPASSWORD)
Generates a new passphrase recogniser object using the DES-based crypt() algorithm, from an RFC 2307
string. The string must consist of "{CRYPT}" (case insensitive) followed by an acceptable crypt
string.
METHODS
$ppr->fold
Returns a truth value indicating whether passphrase folding is used.
$ppr->initial
Returns the initial block, as a string of eight bytes.
$ppr->initial_base64
Returns the initial block, as a string of eleven base 64 digits.
$ppr->nrounds
Returns the number of encryption rounds, as a Perl integer.
$ppr->nrounds_base64_4
Returns the number of encryption rounds, as a string of four base 64 digits.
$ppr->salt
Returns the salt, as a Perl integer.
$ppr->salt_base64_2
Returns the salt, as a string of two base 64 digits. "die"s if it doesn't fit into two digits.
$ppr->salt_base64_4
Returns the salt, as a string of four base 64 digits.
$ppr->hash
Returns the hash value, as a string of eight bytes.
$ppr->hash_base64
Returns the hash value, as a string of eleven base 64 digits.
$ppr->match(PASSPHRASE)
$ppr->as_crypt
$ppr->as_rfc2307
These methods are part of the standard Authen::Passphrase interface.
SEE ALSO
Authen::Passphrase, Crypt::UnixCrypt_XS
AUTHOR
Andrew Main (Zefram) <zefram@fysh.org>
COPYRIGHT
Copyright (C) 2006, 2007, 2009, 2010, 2012 Andrew Main (Zefram) <zefram@fysh.org>
LICENSE
This module is free software; you can redistribute it and/or modify it under the same terms as Perl
itself.