1Digest(3pm) Perl Programmers Reference Guide Digest(3pm)
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6 Digest - Modules that calculate message digests
7
9 $md5 = Digest->new("MD5");
10 $sha1 = Digest->new("SHA-1");
11 $sha256 = Digest->new("SHA-256");
12 $sha384 = Digest->new("SHA-384");
13 $sha512 = Digest->new("SHA-512");
14 $hmac = Digest->HMAC_MD5($key);
16
18 The "Digest::" modules calculate digests, also called "fingerprints" or
19 "hashes", of some data, called a message. The digest is (usually) some
20 small/fixed size string. The actual size of the digest depend of the
21 algorithm used. The message is simply a sequence of arbitrary bytes or
22 bits.
23 An important property of the digest algorithms is that the digest is
25 likely to change if the message change in some way. Another property
26 is that digest functions are one-way functions, that is it should be
27 hard to find a message that correspond to some given digest.
28 Algorithms differ in how "likely" and how "hard", as well as how
29 efficient they are to compute.
30 Note that the properties of the algorithms change over time, as the
32 algorithms are analyzed and machines grow faster. If your application
33 for instance depends on it being "impossible" to generate the same
34 digest for a different message it is wise to make it easy to plug in
35 stronger algorithms as the one used grow weaker. Using the interface
36 documented here should make it easy to change algorithms later.
37 All "Digest::" modules provide the same programming interface. A
39 functional interface for simple use, as well as an object oriented
40 interface that can handle messages of arbitrary length and which can
41 read files directly.
42 The digest can be delivered in three formats:
44 binary This is the most compact form, but it is not well suited for
46 printing or embedding in places that can't handle arbitrary
47 data.
48 hex A twice as long string of lowercase hexadecimal digits.
50 base64 A string of portable printable characters. This is the base64
52 encoded representation of the digest with any trailing padding
53 removed. The string will be about 30% longer than the binary
54 version. MIME::Base64 tells you more about this encoding.
55 The functional interface is simply importable functions with the same
57 name as the algorithm. The functions take the message as argument and
58 return the digest. Example:
59 use Digest::MD5 qw(md5);
61 $digest = md5($message);
62 There are also versions of the functions with "_hex" or "_base64"
64 appended to the name, which returns the digest in the indicated form.
65
67 The following methods are available for all "Digest::" modules:
68 $ctx = Digest->XXX($arg,...)
70 $ctx = Digest->new(XXX => $arg,...)
71 $ctx = Digest::XXX->new($arg,...)
72 The constructor returns some object that encapsulate the state of
73 the message-digest algorithm. You can add data to the object and
74 finally ask for the digest. The "XXX" should of course be replaced
75 by the proper name of the digest algorithm you want to use.
76 The two first forms are simply syntactic sugar which automatically
78 load the right module on first use. The second form allow you to
79 use algorithm names which contains letters which are not legal perl
80 identifiers, e.g. "SHA-1". If no implementation for the given
81 algorithm can be found, then an exception is raised.
82 If new() is called as an instance method (i.e. $ctx->new) it will
84 just reset the state the object to the state of a newly created
85 object. No new object is created in this case, and the return
86 value is the reference to the object (i.e. $ctx).
87 $other_ctx = $ctx->clone
89 The clone method creates a copy of the digest state object and
90 returns a reference to the copy.
91 $ctx->reset
93 This is just an alias for $ctx->new.
94 $ctx->add( $data )
96 $ctx->add( $chunk1, $chunk2, ... )
97 The string value of the $data provided as argument is appended to
98 the message we calculate the digest for. The return value is the
99 $ctx object itself.
100 If more arguments are provided then they are all appended to the
102 message, thus all these lines will have the same effect on the
103 state of the $ctx object:
104 $ctx->add("a"); $ctx->add("b"); $ctx->add("c");
106 $ctx->add("a")->add("b")->add("c");
107 $ctx->add("a", "b", "c");
108 $ctx->add("abc");
109 Most algorithms are only defined for strings of bytes and this
111 method might therefore croak if the provided arguments contain
112 chars with ordinal number above 255.
113 $ctx->addfile( $io_handle )
115 The $io_handle is read until EOF and the content is appended to the
116 message we calculate the digest for. The return value is the $ctx
117 object itself.
118 The addfile() method will croak() if it fails reading data for some
120 reason. If it croaks it is unpredictable what the state of the
121 $ctx object will be in. The addfile() method might have been able
122 to read the file partially before it failed. It is probably wise
123 to discard or reset the $ctx object if this occurs.
124 In most cases you want to make sure that the $io_handle is in
126 "binmode" before you pass it as argument to the addfile() method.
127 $ctx->add_bits( $data, $nbits )
129 $ctx->add_bits( $bitstring )
130 The add_bits() method is an alternative to add() that allow partial
131 bytes to be appended to the message. Most users should just ignore
132 this method as partial bytes is very unlikely to be of any
133 practical use.
134 The two argument form of add_bits() will add the first $nbits bits
136 from $data. For the last potentially partial byte only the high
137 order "$nbits % 8" bits are used. If $nbits is greater than
138 "length($data) * 8", then this method would do the same as
139 "$ctx->add($data)".
140 The one argument form of add_bits() takes a $bitstring of "1" and
142 "0" chars as argument. It's a shorthand for
143 "$ctx->add_bits(pack("B*", $bitstring), length($bitstring))".
144 The return value is the $ctx object itself.
146 This example shows two calls that should have the same effect:
148 $ctx->add_bits("111100001010");
150 $ctx->add_bits("\xF0\xA0", 12);
151 Most digest algorithms are byte based and for these it is not
153 possible to add bits that are not a multiple of 8, and the
154 add_bits() method will croak if you try.
155 $ctx->digest
157 Return the binary digest for the message.
158 Note that the "digest" operation is effectively a destructive,
160 read-once operation. Once it has been performed, the $ctx object is
161 automatically "reset" and can be used to calculate another digest
162 value. Call $ctx->clone->digest if you want to calculate the
163 digest without resetting the digest state.
164 $ctx->hexdigest
166 Same as $ctx->digest, but will return the digest in hexadecimal
167 form.
168 $ctx->b64digest
170 Same as $ctx->digest, but will return the digest as a base64
171 encoded string.
172
174 This table should give some indication on the relative speed of
175 different algorithms. It is sorted by throughput based on a benchmark
176 done with of some implementations of this API:
177 Algorithm Size Implementation MB/s
179 MD4 128 Digest::MD4 v1.3 165.0
181 MD5 128 Digest::MD5 v2.33 98.8
182 SHA-256 256 Digest::SHA2 v1.1.0 66.7
183 SHA-1 160 Digest::SHA v4.3.1 58.9
184 SHA-1 160 Digest::SHA1 v2.10 48.8
185 SHA-256 256 Digest::SHA v4.3.1 41.3
186 Haval-256 256 Digest::Haval256 v1.0.4 39.8
187 SHA-384 384 Digest::SHA2 v1.1.0 19.6
188 SHA-512 512 Digest::SHA2 v1.1.0 19.3
189 SHA-384 384 Digest::SHA v4.3.1 19.2
190 SHA-512 512 Digest::SHA v4.3.1 19.2
191 Whirlpool 512 Digest::Whirlpool v1.0.2 13.0
192 MD2 128 Digest::MD2 v2.03 9.5
193 Adler-32 32 Digest::Adler32 v0.03 1.3
195 CRC-16 16 Digest::CRC v0.05 1.1
196 CRC-32 32 Digest::CRC v0.05 1.1
197 MD5 128 Digest::Perl::MD5 v1.5 1.0
198 CRC-CCITT 16 Digest::CRC v0.05 0.8
199 These numbers was achieved Apr 2004 with ActivePerl-5.8.3 running under
201 Linux on a P4 2.8 GHz CPU. The last 5 entries differ by being pure
202 perl implementations of the algorithms, which explains why they are so
203 slow.
204
206 Digest::Adler32, Digest::CRC, Digest::Haval256, Digest::HMAC,
207 Digest::MD2, Digest::MD4, Digest::MD5, Digest::SHA, Digest::SHA1,
208 Digest::SHA2, Digest::Whirlpool
209 New digest implementations should consider subclassing from
211 Digest::base.
212 MIME::Base64
214 http://en.wikipedia.org/wiki/Cryptographic_hash_function
216
218 Gisle Aas <gisle@aas.no>
219 The "Digest::" interface is based on the interface originally developed
221 by Neil Winton for his "MD5" module.
222 This library is free software; you can redistribute it and/or modify it
224 under the same terms as Perl itself.
225 Copyright 1998-2006 Gisle Aas.
227 Copyright 1995,1996 Neil Winton.
228perl v5.12.4 2011-11-04 Digest(3pm)