1Digest::MD5(3pm)       Perl Programmers Reference Guide       Digest::MD5(3pm)
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3
4

NAME

6       Digest::MD5 - Perl interface to the MD5 Algorithm
7

SYNOPSIS

9        # Functional style
10        use Digest::MD5 qw(md5 md5_hex md5_base64);
11
12        $digest = md5($data);
13        $digest = md5_hex($data);
14        $digest = md5_base64($data);
15
16        # OO style
17        use Digest::MD5;
18
19        $ctx = Digest::MD5->new;
20
21        $ctx->add($data);
22        $ctx->addfile(*FILE);
23
24        $digest = $ctx->digest;
25        $digest = $ctx->hexdigest;
26        $digest = $ctx->b64digest;
27

DESCRIPTION

29       The "Digest::MD5" module allows you to use the RSA Data Security Inc.
30       MD5 Message Digest algorithm from within Perl programs.  The algorithm
31       takes as input a message of arbitrary length and produces as output a
32       128-bit "fingerprint" or "message digest" of the input.
33
34       Note that the MD5 algorithm is not as strong as it used to be.  It has
35       since 2005 been easy to generate different messages that produce the
36       same MD5 digest.  It still seems hard to generate messages that produce
37       a given digest, but it is probably wise to move to stronger algorithms
38       for applications that depend on the digest to uniquely identify a
39       message.
40
41       The "Digest::MD5" module provide a procedural interface for simple use,
42       as well as an object oriented interface that can handle messages of
43       arbitrary length and which can read files directly.
44

FUNCTIONS

46       The following functions are provided by the "Digest::MD5" module.  None
47       of these functions are exported by default.
48
49       md5($data,...)
50           This function will concatenate all arguments, calculate the MD5
51           digest of this "message", and return it in binary form.  The
52           returned string will be 16 bytes long.
53
54           The result of md5("a", "b", "c") will be exactly the same as the
55           result of md5("abc").
56
57       md5_hex($data,...)
58           Same as md5(), but will return the digest in hexadecimal form. The
59           length of the returned string will be 32 and it will only contain
60           characters from this set: '0'..'9' and 'a'..'f'.
61
62       md5_base64($data,...)
63           Same as md5(), but will return the digest as a base64 encoded
64           string.  The length of the returned string will be 22 and it will
65           only contain characters from this set: 'A'..'Z', 'a'..'z',
66           '0'..'9', '+' and '/'.
67
68           Note that the base64 encoded string returned is not padded to be a
69           multiple of 4 bytes long.  If you want interoperability with other
70           base64 encoded md5 digests you might want to append the redundant
71           string "==" to the result.
72

METHODS

74       The object oriented interface to "Digest::MD5" is described in this
75       section.  After a "Digest::MD5" object has been created, you will add
76       data to it and finally ask for the digest in a suitable format.  A
77       single object can be used to calculate multiple digests.
78
79       The following methods are provided:
80
81       $md5 = Digest::MD5->new
82           The constructor returns a new "Digest::MD5" object which
83           encapsulate the state of the MD5 message-digest algorithm.
84
85           If called as an instance method (i.e. $md5->new) it will just reset
86           the state the object to the state of a newly created object.  No
87           new object is created in this case.
88
89       $md5->reset
90           This is just an alias for $md5->new.
91
92       $md5->clone
93           This a copy of the $md5 object. It is useful when you do not want
94           to destroy the digests state, but need an intermediate value of the
95           digest, e.g. when calculating digests iteratively on a continuous
96           data stream.  Example:
97
98               my $md5 = Digest::MD5->new;
99               while (<>) {
100                   $md5->add($_);
101                   print "Line $.: ", $md5->clone->hexdigest, "\n";
102               }
103
104       $md5->add($data,...)
105           The $data provided as argument are appended to the message we
106           calculate the digest for.  The return value is the $md5 object
107           itself.
108
109           All these lines will have the same effect on the state of the $md5
110           object:
111
112               $md5->add("a"); $md5->add("b"); $md5->add("c");
113               $md5->add("a")->add("b")->add("c");
114               $md5->add("a", "b", "c");
115               $md5->add("abc");
116
117       $md5->addfile($io_handle)
118           The $io_handle will be read until EOF and its content appended to
119           the message we calculate the digest for.  The return value is the
120           $md5 object itself.
121
122           The addfile() method will croak() if it fails reading data for some
123           reason.  If it croaks it is unpredictable what the state of the
124           $md5 object will be in. The addfile() method might have been able
125           to read the file partially before it failed.  It is probably wise
126           to discard or reset the $md5 object if this occurs.
127
128           In most cases you want to make sure that the $io_handle is in
129           "binmode" before you pass it as argument to the addfile() method.
130
131       $md5->add_bits($data, $nbits)
132       $md5->add_bits($bitstring)
133           Since the MD5 algorithm is byte oriented you might only add bits as
134           multiples of 8, so you probably want to just use add() instead.
135           The add_bits() method is provided for compatibility with other
136           digest implementations.  See Digest for description of the
137           arguments that add_bits() take.
138
139       $md5->digest
140           Return the binary digest for the message.  The returned string will
141           be 16 bytes long.
142
143           Note that the "digest" operation is effectively a destructive,
144           read-once operation. Once it has been performed, the "Digest::MD5"
145           object is automatically "reset" and can be used to calculate
146           another digest value.  Call $md5->clone->digest if you want to
147           calculate the digest without resetting the digest state.
148
149       $md5->hexdigest
150           Same as $md5->digest, but will return the digest in hexadecimal
151           form. The length of the returned string will be 32 and it will only
152           contain characters from this set: '0'..'9' and 'a'..'f'.
153
154       $md5->b64digest
155           Same as $md5->digest, but will return the digest as a base64
156           encoded string.  The length of the returned string will be 22 and
157           it will only contain characters from this set: 'A'..'Z', 'a'..'z',
158           '0'..'9', '+' and '/'.
159
160           The base64 encoded string returned is not padded to be a multiple
161           of 4 bytes long.  If you want interoperability with other base64
162           encoded md5 digests you might want to append the string "==" to the
163           result.
164

EXAMPLES

166       The simplest way to use this library is to import the md5_hex()
167       function (or one of its cousins):
168
169           use Digest::MD5 qw(md5_hex);
170           print "Digest is ", md5_hex("foobarbaz"), "\n";
171
172       The above example would print out the message:
173
174           Digest is 6df23dc03f9b54cc38a0fc1483df6e21
175
176       The same checksum can also be calculated in OO style:
177
178           use Digest::MD5;
179
180           $md5 = Digest::MD5->new;
181           $md5->add('foo', 'bar');
182           $md5->add('baz');
183           $digest = $md5->hexdigest;
184
185           print "Digest is $digest\n";
186
187       With OO style you can break the message arbitrary.  This means that we
188       are no longer limited to have space for the whole message in memory,
189       i.e.  we can handle messages of any size.
190
191       This is useful when calculating checksum for files:
192
193           use Digest::MD5;
194
195           my $file = shift || "/etc/passwd";
196           open(FILE, $file) or die "Can't open '$file': $!";
197           binmode(FILE);
198
199           $md5 = Digest::MD5->new;
200           while (<FILE>) {
201               $md5->add($_);
202           }
203           close(FILE);
204           print $md5->b64digest, " $file\n";
205
206       Or we can use the addfile method for more efficient reading of the
207       file:
208
209           use Digest::MD5;
210
211           my $file = shift || "/etc/passwd";
212           open(FILE, $file) or die "Can't open '$file': $!";
213           binmode(FILE);
214
215           print Digest::MD5->new->addfile(*FILE)->hexdigest, " $file\n";
216
217       Perl 5.8 support Unicode characters in strings.  Since the MD5
218       algorithm is only defined for strings of bytes, it can not be used on
219       strings that contains chars with ordinal number above 255.  The MD5
220       functions and methods will croak if you try to feed them such input
221       data:
222
223           use Digest::MD5 qw(md5_hex);
224
225           my $str = "abc\x{300}";
226           print md5_hex($str), "\n";  # croaks
227           # Wide character in subroutine entry
228
229       What you can do is calculate the MD5 checksum of the UTF-8
230       representation of such strings.  This is achieved by filtering the
231       string through encode_utf8() function:
232
233           use Digest::MD5 qw(md5_hex);
234           use Encode qw(encode_utf8);
235
236           my $str = "abc\x{300}";
237           print md5_hex(encode_utf8($str)), "\n";
238           # 8c2d46911f3f5a326455f0ed7a8ed3b3
239

SEE ALSO

241       Digest, Digest::MD2, Digest::SHA, Digest::HMAC
242
243       md5sum(1)
244
245       RFC 1321
246
247       http://en.wikipedia.org/wiki/MD5
248
249       The paper "How to Break MD5 and Other Hash Functions" by Xiaoyun Wang
250       and Hongbo Yu.
251
253       This library is free software; you can redistribute it and/or modify it
254       under the same terms as Perl itself.
255
256        Copyright 1998-2003 Gisle Aas.
257        Copyright 1995-1996 Neil Winton.
258        Copyright 1991-1992 RSA Data Security, Inc.
259
260       The MD5 algorithm is defined in RFC 1321. This implementation is
261       derived from the reference C code in RFC 1321 which is covered by the
262       following copyright statement:
263
264       ยท   Copyright (C) 1991-2, RSA Data Security, Inc. Created 1991. All
265           rights reserved.
266
267           License to copy and use this software is granted provided that it
268           is identified as the "RSA Data Security, Inc. MD5 Message-Digest
269           Algorithm" in all material mentioning or referencing this software
270           or this function.
271
272           License is also granted to make and use derivative works provided
273           that such works are identified as "derived from the RSA Data
274           Security, Inc. MD5 Message-Digest Algorithm" in all material
275           mentioning or referencing the derived work.
276
277           RSA Data Security, Inc. makes no representations concerning either
278           the merchantability of this software or the suitability of this
279           software for any particular purpose. It is provided "as is" without
280           express or implied warranty of any kind.
281
282           These notices must be retained in any copies of any part of this
283           documentation and/or software.
284
285       This copyright does not prohibit distribution of any version of Perl
286       containing this extension under the terms of the GNU or Artistic
287       licenses.
288

AUTHORS

290       The original "MD5" interface was written by Neil Winton
291       ("N.Winton@axion.bt.co.uk").
292
293       The "Digest::MD5" module is written by Gisle Aas
294       <gisle@ActiveState.com>.
295
296
297
298perl v5.12.4                      2011-06-07                  Digest::MD5(3pm)
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