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. Algo‐
28 rithms differ in how "likely" and how "hard", as well as how efficient
29 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 func‐
39 tional interface for simple use, as well as an object oriented inter‐
40 face that can handle messages of arbitrary length and which can read
41 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 The $data provided as argument are appended to the message we cal‐
97 culate the digest for. The return value is the $ctx object itself.
98 $ctx->addfile( $io_handle )
100 The $io_handle is read until EOF and the content is appended to the
101 message we calculate the digest for. The return value is the $ctx
102 object itself.
103 $ctx->add_bits( $data, $nbits )
105 $ctx->add_bits( $bitstring )
106 The bits provided are appended to the message we calculate the
107 digest for. The return value is the $ctx object itself.
108 The two argument form of add_bits() will add the first $nbits bits
110 from data. For the last potentially partial byte only the high
111 order "$nbits % 8" bits are used. If $nbits is greater than
112 "length($data) * 8", then this method would do the same as
113 "$ctx->add($data)", that is $nbits is silently ignored.
114 The one argument form of add_bits() takes a $bitstring of "1" and
116 "0" chars as argument. It's a shorthand for
117 "$ctx->add_bits(pack("B*", $bitstring), length($bitstring))".
118 This example shows two calls that should have the same effect:
120 $ctx->add_bits("111100001010");
122 $ctx->add_bits("\xF0\xA0", 12);
123 Most digest algorithms are byte based. For those it is not possi‐
125 ble to add bits that are not a multiple of 8, and the add_bits()
126 method will croak if you try.
127 $ctx->digest
129 Return the binary digest for the message.
130 Note that the "digest" operation is effectively a destructive,
132 read-once operation. Once it has been performed, the $ctx object is
133 automatically "reset" and can be used to calculate another digest
134 value. Call $ctx->clone->digest if you want to calculate the
135 digest without reseting the digest state.
136 $ctx->hexdigest
138 Same as $ctx->digest, but will return the digest in hexadecimal
139 form.
140 $ctx->b64digest
142 Same as $ctx->digest, but will return the digest as a base64
143 encoded string.
144
146 This table should give some indication on the relative speed of differ‐
147 ent algorithms. It is sorted by throughput based on a benchmark done
148 with of some implementations of this API:
149 Algorithm Size Implementation MB/s
151 MD4 128 Digest::MD4 v1.3 165.0
153 MD5 128 Digest::MD5 v2.33 98.8
154 SHA-256 256 Digest::SHA2 v1.1.0 66.7
155 SHA-1 160 Digest::SHA v4.3.1 58.9
156 SHA-1 160 Digest::SHA1 v2.10 48.8
157 SHA-256 256 Digest::SHA v4.3.1 41.3
158 Haval-256 256 Digest::Haval256 v1.0.4 39.8
159 SHA-384 384 Digest::SHA2 v1.1.0 19.6
160 SHA-512 512 Digest::SHA2 v1.1.0 19.3
161 SHA-384 384 Digest::SHA v4.3.1 19.2
162 SHA-512 512 Digest::SHA v4.3.1 19.2
163 Whirlpool 512 Digest::Whirlpool v1.0.2 13.0
164 MD2 128 Digest::MD2 v2.03 9.5
165 Adler-32 32 Digest::Adler32 v0.03 1.3
167 CRC-16 16 Digest::CRC v0.05 1.1
168 CRC-32 32 Digest::CRC v0.05 1.1
169 MD5 128 Digest::Perl::MD5 v1.5 1.0
170 CRC-CCITT 16 Digest::CRC v0.05 0.8
171 These numbers was achieved Apr 2004 with ActivePerl-5.8.3 running under
173 Linux on a P4 2.8 GHz CPU. The last 5 entries differ by being pure
174 perl implementations of the algorithms, which explains why they are so
175 slow.
176
178 Digest::Adler32, Digest::CRC, Digest::Haval256, Digest::HMAC,
179 Digest::MD2, Digest::MD4, Digest::MD5, Digest::SHA, Digest::SHA1,
180 Digest::SHA2, Digest::Whirlpool
181 New digest implementations should consider subclassing from
183 Digest::base.
184 MIME::Base64
186
188 Gisle Aas <gisle@aas.no>
189 The "Digest::" interface is based on the interface originally developed
191 by Neil Winton for his "MD5" module.
192 This library is free software; you can redistribute it and/or modify it
194 under the same terms as Perl itself.
195 Copyright 1998-2001,2003-2004 Gisle Aas.
197 Copyright 1995-1996 Neil Winton.
198perl v5.8.8 2001-09-21 Digest(3pm)