1Authen::Passphrase::DESUCsreyrptC(o3n)tributed Perl DocuAmuetnhteant:i:oPnassphrase::DESCrypt(3)
2
6 Authen::Passphrase::DESCrypt - passphrases using the DES-based Unix
7 crypt()
8
10 use Authen::Passphrase::DESCrypt;
11 $ppr = Authen::Passphrase::DESCrypt->new(
13 salt_base64 => "my",
14 hash_base64 => "TYK.j.88/9s");
15 $ppr = Authen::Passphrase::DESCrypt->new(
17 salt_random => 12,
18 passphrase => "passphrase");
19 $ppr = Authen::Passphrase::DESCrypt
21 ->from_crypt('myTYK.j.88/9s');
22 $ppr = Authen::Passphrase::DESCrypt->new(
24 fold => 1,
25 initial => "xyzzy!!!",
26 nrounds => 500,
27 salt_base64 => "quux",
28 hash_base64 => "QCKcHlgVsRY");
29 $fold = $ppr->fold;
31 $initial = $ppr->initial;
32 $initial_base64 = $ppr->initial_base64;
33 $nrounds = $ppr->nrounds;
34 $nrounds_base64 = $ppr->nrounds_base64_4;
35 $salt = $ppr->salt;
36 $salt_base64 = $ppr->salt_base64_2;
37 $salt_base64 = $ppr->salt_base64_4;
38 $hash = $ppr->hash;
39 $hash_base64 = $ppr->hash_base64;
40 if($ppr->match($passphrase)) { ...
42 $passwd = $ppr->as_crypt;
44 $userPassword = $ppr->as_rfc2307;
45
47 An object of this class encapsulates a passphrase hashed using some
48 form of the DES-based Unix crypt() hash function. This is a subclass
49 of Authen::Passphrase, and this document assumes that the reader is
50 familiar with the documentation for that class.
51 The crypt() function in a modern Unix actually supports several
53 different passphrase schemes. That is not what this class is about.
54 This class is concerned only with one family of schemes, variants of
55 the DES-based scheme that crypt() originally implemented, which
56 confusingly is usually referred to merely as "crypt()". To handle the
57 whole range of passphrase schemes supported by the modern crypt(), see
58 the from_crypt constructor and the as_crypt method in
59 Authen::Passphrase.
60 Warning: this password scheme is weak by modern standards, and in any
62 case does not support a large password space. Cracking crypt()ed
63 passwords has been a routine activity since the early 1990s. This
64 scheme is supported for compatibility reasons only, and should not be
65 used except when compatibility is required. Do not use this in the
66 design of any new system or for new passwords in any system that
67 supports better passphrase schemes.
68 The traditional DES-based Unix crypt() password scheme
70 The traditional Unix crypt() password scheme is based on the DES block
71 encryption algorithm. Using the password as a 56-bit key, it passes a
72 64-bit data block, initialised to zero, through the encryption function
73 25 times, and the hash is the 64-bit output of this process. A 12-bit
74 salt is used to tweak the encryption algorithm.
75 The 56-bit key is extracted from the password in a very poor way. Only
77 the first eight bytes of the password are used, and any remainder is
78 ignored. This makes it impossible to use a passphrase, rather than a
79 password, hence the terminology in this section. Of the eight bytes
80 used, the top bit is also ignored; this function hails from the days of
81 pure ASCII.
82 A password hash of this scheme is conventionally represented in ASCII
84 as a 13-character string using a base 64 encoding. The base 64 digits
85 are ".", "/", "0" to "9", "A" to "Z", "a" to "z" (in ASCII order). The
86 first two characters give the 12-bit salt. The remaining eleven
87 characters give the 64-bit hash. Because the base 64 encoding can
88 represent 66 bits in eleven digits, more than the 64 required, the last
89 character of the string can only take sixteen of the base 64 digit
90 values.
91 Variant DES-based Unix crypt() passphrase schemes
93 To make password cracking more difficult, historically some Unix sites
94 modified the crypt() function to be incompatible with the standard one.
95 This was easily achieved by initialising the data block to something
96 other than the standard all-bits-zero. Another variation used was to
97 increase the number of encryption rounds, which makes cracking take
98 longer in addition to being non-standard. Password hashes on such a
99 system looked normal but were not interoperable with standard crypt()
100 implementations. To interpret them properly it is necessary to know
101 the modified parameters.
102 BSDi standardised an extended DES-based scheme. The salt is extended
104 to 24 bits, and the number of encryption rounds is variable.
105 Passphrases longer than 8 characters are handled by an additional step
106 that folds (hashes) them down to 8 characters, rather than just
107 throwing away the characters after the eighth. Passphrase hashes in
108 this scheme are conventionally represented in ASCII as a "_" followed
109 by 19 characters of base 64. The first four base 64 digits give the
110 number of encryption rounds, the next four give the salt, and the
111 remaining eleven give the hash.
112
114 Authen::Passphrase::DESCrypt->new(ATTR => VALUE, ...)
115 Generates a new passphrase recogniser object using the generalised
116 DES-based crypt() algorithm. The following attributes may be
117 given:
118 fold
120 Truth value indicating whether the BSDi passphrase folding
121 scheme should be used for long passphrases. Default false, for
122 compatibility with the original DES-based scheme.
123 initial
125 The initial data block to encrypt, as a string of exactly eight
126 bytes. Default all bits zero, for compatibility with the
127 original DES-based scheme.
128 initial_base64
130 The initial data block to encrypt, as a string of eleven base
131 64 digits.
132 nrounds
134 The number of encryption rounds to use, as a Perl integer.
135 Default 25, for compatibility with the original DES-based
136 scheme.
137 nrounds_base64
139 The number of encryption rounds to use, as a string of four
140 base 64 digits.
141 salt
143 The salt, as an integer in the range [0, 16777216).
144 salt_base64
146 The salt, as a string of two or four base 64 digits.
147 salt_random
149 Causes salt to be generated randomly. The value given for this
150 attribute must be either 12 or 24, giving the number of bits of
151 salt to generate. The source of randomness may be controlled
152 by the facility described in Data::Entropy.
153 hash
155 The hash (output of encryption), as a string of exactly eight
156 bytes.
157 hash_base64
159 The hash, as a string of eleven base 64 digits.
160 passphrase
162 A passphrase that will be accepted.
163 The salt must be given, and either the hash or the passphrase. The
165 other parameters default to those used in the original DES-based
166 crypt().
167 Authen::Passphrase::DESCrypt->from_crypt(PASSWD)
169 Generates a new passphrase recogniser object using the DES-based
170 crypt() algorithm, from a crypt string. Two forms of crypt string
171 are supported.
172 The first form of crypt string must consist of 13 base 64 digits.
174 The first two give the salt, and the next eleven give the hash.
175 Long passphrases are not folded, the initial block is all bits
176 zero, and 25 encryption rounds are performed.
177 The second form of crypt string must consist of an "_" followed by
179 19 base 64 digits. The first four give the number of encryption
180 rounds, the next four give the salt, and the next eleven give the
181 hash. Long passphrases are folded, and the initial block is all
182 bits zero.
183 Authen::Passphrase::DESCrypt->from_rfc2307(USERPASSWORD)
185 Generates a new passphrase recogniser object using the DES-based
186 crypt() algorithm, from an RFC 2307 string. The string must
187 consist of "{CRYPT}" (case insensitive) followed by an acceptable
188 crypt string.
189
191 $ppr->fold
192 Returns a truth value indicating whether passphrase folding is
193 used.
194 $ppr->initial
196 Returns the initial block, as a string of eight bytes.
197 $ppr->initial_base64
199 Returns the initial block, as a string of eleven base 64 digits.
200 $ppr->nrounds
202 Returns the number of encryption rounds, as a Perl integer.
203 $ppr->nrounds_base64_4
205 Returns the number of encryption rounds, as a string of four base
206 64 digits.
207 $ppr->salt
209 Returns the salt, as a Perl integer.
210 $ppr->salt_base64_2
212 Returns the salt, as a string of two base 64 digits. "die"s if it
213 doesn't fit into two digits.
214 $ppr->salt_base64_4
216 Returns the salt, as a string of four base 64 digits.
217 $ppr->hash
219 Returns the hash value, as a string of eight bytes.
220 $ppr->hash_base64
222 Returns the hash value, as a string of eleven base 64 digits.
223 $ppr->match(PASSPHRASE)
225 $ppr->as_crypt
226 $ppr->as_rfc2307
227 These methods are part of the standard Authen::Passphrase
228 interface.
229
231 Authen::Passphrase, Crypt::UnixCrypt_XS
232
234 Andrew Main (Zefram) <zefram@fysh.org>
235
237 Copyright (C) 2006, 2007, 2009, 2010, 2012 Andrew Main (Zefram)
238 <zefram@fysh.org>
239
241 This module is free software; you can redistribute it and/or modify it
242 under the same terms as Perl itself.
243perl v5.30.1 2020-01-29 Authen::Passphrase::DESCrypt(3)