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129 | .\" ======================================================================== | |
130 | .\" | |
131 | .IX Title "Digest 3" | |
132 | .TH Digest 3 "2001-09-21" "perl v5.8.8" "Perl Programmers Reference Guide" | |
133 | .SH "NAME" | |
134 | Digest \- Modules that calculate message digests | |
135 | .SH "SYNOPSIS" | |
136 | .IX Header "SYNOPSIS" | |
137 | .Vb 5 | |
138 | \& $md5 = Digest->new("MD5"); | |
139 | \& $sha1 = Digest->new("SHA-1"); | |
140 | \& $sha256 = Digest->new("SHA-256"); | |
141 | \& $sha384 = Digest->new("SHA-384"); | |
142 | \& $sha512 = Digest->new("SHA-512"); | |
143 | .Ve | |
144 | .PP | |
145 | .Vb 1 | |
146 | \& $hmac = Digest->HMAC_MD5($key); | |
147 | .Ve | |
148 | .SH "DESCRIPTION" | |
149 | .IX Header "DESCRIPTION" | |
150 | The \f(CW\*(C`Digest::\*(C'\fR modules calculate digests, also called \*(L"fingerprints\*(R" | |
151 | or \*(L"hashes\*(R", of some data, called a message. The digest is (usually) | |
152 | some small/fixed size string. The actual size of the digest depend of | |
153 | the algorithm used. The message is simply a sequence of arbitrary | |
154 | bytes or bits. | |
155 | .PP | |
156 | An important property of the digest algorithms is that the digest is | |
157 | \&\fIlikely\fR to change if the message change in some way. Another | |
158 | property is that digest functions are one-way functions, that is it | |
159 | should be \fIhard\fR to find a message that correspond to some given | |
160 | digest. Algorithms differ in how \*(L"likely\*(R" and how \*(L"hard\*(R", as well as | |
161 | how efficient they are to compute. | |
162 | .PP | |
163 | Note that the properties of the algorithms change over time, as the | |
164 | algorithms are analyzed and machines grow faster. If your application | |
165 | for instance depends on it being \*(L"impossible\*(R" to generate the same | |
166 | digest for a different message it is wise to make it easy to plug in | |
167 | stronger algorithms as the one used grow weaker. Using the interface | |
168 | documented here should make it easy to change algorithms later. | |
169 | .PP | |
170 | All \f(CW\*(C`Digest::\*(C'\fR modules provide the same programming interface. A | |
171 | functional interface for simple use, as well as an object oriented | |
172 | interface that can handle messages of arbitrary length and which can | |
173 | read files directly. | |
174 | .PP | |
175 | The digest can be delivered in three formats: | |
176 | .IP "\fIbinary\fR" 8 | |
177 | .IX Item "binary" | |
178 | This is the most compact form, but it is not well suited for printing | |
179 | or embedding in places that can't handle arbitrary data. | |
180 | .IP "\fIhex\fR" 8 | |
181 | .IX Item "hex" | |
182 | A twice as long string of lowercase hexadecimal digits. | |
183 | .IP "\fIbase64\fR" 8 | |
184 | .IX Item "base64" | |
185 | A string of portable printable characters. This is the base64 encoded | |
186 | representation of the digest with any trailing padding removed. The | |
187 | string will be about 30% longer than the binary version. | |
188 | MIME::Base64 tells you more about this encoding. | |
189 | .PP | |
190 | The functional interface is simply importable functions with the same | |
191 | name as the algorithm. The functions take the message as argument and | |
192 | return the digest. Example: | |
193 | .PP | |
194 | .Vb 2 | |
195 | \& use Digest::MD5 qw(md5); | |
196 | \& $digest = md5($message); | |
197 | .Ve | |
198 | .PP | |
199 | There are also versions of the functions with \*(L"_hex\*(R" or \*(L"_base64\*(R" | |
200 | appended to the name, which returns the digest in the indicated form. | |
201 | .SH "OO INTERFACE" | |
202 | .IX Header "OO INTERFACE" | |
203 | The following methods are available for all \f(CW\*(C`Digest::\*(C'\fR modules: | |
204 | .IP "$ctx = Digest\->\s-1XXX\s0($arg,...)" 4 | |
205 | .IX Item "$ctx = Digest->XXX($arg,...)" | |
206 | .PD 0 | |
207 | .ie n .IP "$ctx = Digest\->new(\s-1XXX\s0 => $arg,...)" 4 | |
208 | .el .IP "$ctx = Digest\->new(\s-1XXX\s0 => \f(CW$arg\fR,...)" 4 | |
209 | .IX Item "$ctx = Digest->new(XXX => $arg,...)" | |
210 | .IP "$ctx = Digest::XXX\->new($arg,...)" 4 | |
211 | .IX Item "$ctx = Digest::XXX->new($arg,...)" | |
212 | .PD | |
213 | The constructor returns some object that encapsulate the state of the | |
214 | message-digest algorithm. You can add data to the object and finally | |
215 | ask for the digest. The \*(L"\s-1XXX\s0\*(R" should of course be replaced by the proper | |
216 | name of the digest algorithm you want to use. | |
217 | .Sp | |
218 | The two first forms are simply syntactic sugar which automatically | |
219 | load the right module on first use. The second form allow you to use | |
220 | algorithm names which contains letters which are not legal perl | |
221 | identifiers, e.g. \*(L"\s-1SHA\-1\s0\*(R". If no implementation for the given algorithm | |
222 | can be found, then an exception is raised. | |
223 | .Sp | |
224 | If \fInew()\fR is called as an instance method (i.e. \f(CW$ctx\fR\->new) it will just | |
225 | reset the state the object to the state of a newly created object. No | |
226 | new object is created in this case, and the return value is the | |
227 | reference to the object (i.e. \f(CW$ctx\fR). | |
228 | .ie n .IP "$other_ctx = $ctx\->clone" 4 | |
229 | .el .IP "$other_ctx = \f(CW$ctx\fR\->clone" 4 | |
230 | .IX Item "$other_ctx = $ctx->clone" | |
231 | The clone method creates a copy of the digest state object and returns | |
232 | a reference to the copy. | |
233 | .IP "$ctx\->reset" 4 | |
234 | .IX Item "$ctx->reset" | |
235 | This is just an alias for \f(CW$ctx\fR\->new. | |
236 | .ie n .IP "$ctx\->add( $data, ... )" 4 | |
237 | .el .IP "$ctx\->add( \f(CW$data\fR, ... )" 4 | |
238 | .IX Item "$ctx->add( $data, ... )" | |
239 | The \f(CW$data\fR provided as argument are appended to the message we | |
240 | calculate the digest for. The return value is the \f(CW$ctx\fR object itself. | |
241 | .ie n .IP "$ctx\->addfile( $io_handle )" 4 | |
242 | .el .IP "$ctx\->addfile( \f(CW$io_handle\fR )" 4 | |
243 | .IX Item "$ctx->addfile( $io_handle )" | |
244 | The \f(CW$io_handle\fR is read until \s-1EOF\s0 and the content is appended to the | |
245 | message we calculate the digest for. The return value is the \f(CW$ctx\fR | |
246 | object itself. | |
247 | .ie n .IP "$ctx\->add_bits( $data\fR, \f(CW$nbits )" 4 | |
248 | .el .IP "$ctx\->add_bits( \f(CW$data\fR, \f(CW$nbits\fR )" 4 | |
249 | .IX Item "$ctx->add_bits( $data, $nbits )" | |
250 | .PD 0 | |
251 | .ie n .IP "$ctx\->add_bits( $bitstring )" 4 | |
252 | .el .IP "$ctx\->add_bits( \f(CW$bitstring\fR )" 4 | |
253 | .IX Item "$ctx->add_bits( $bitstring )" | |
254 | .PD | |
255 | The bits provided are appended to the message we calculate the digest | |
256 | for. The return value is the \f(CW$ctx\fR object itself. | |
257 | .Sp | |
258 | The two argument form of \fIadd_bits()\fR will add the first \f(CW$nbits\fR bits | |
259 | from data. For the last potentially partial byte only the high order | |
260 | \&\f(CW\*(C`$nbits % 8\*(C'\fR bits are used. If \f(CW$nbits\fR is greater than \f(CW\*(C`length($data) * 8\*(C'\fR, then this method would do the same as \f(CW\*(C`$ctx\->add($data)\*(C'\fR, that is \f(CW$nbits\fR is silently ignored. | |
261 | .Sp | |
262 | The one argument form of \fIadd_bits()\fR takes a \f(CW$bitstring\fR of \*(L"1\*(R" and \*(L"0\*(R" | |
263 | chars as argument. It's a shorthand for \f(CW\*(C`$ctx\->add_bits(pack("B*", | |
264 | $bitstring), length($bitstring))\*(C'\fR. | |
265 | .Sp | |
266 | This example shows two calls that should have the same effect: | |
267 | .Sp | |
268 | .Vb 2 | |
269 | \& $ctx->add_bits("111100001010"); | |
270 | \& $ctx->add_bits("\exF0\exA0", 12); | |
271 | .Ve | |
272 | .Sp | |
273 | Most digest algorithms are byte based. For those it is not possible | |
274 | to add bits that are not a multiple of 8, and the \fIadd_bits()\fR method | |
275 | will croak if you try. | |
276 | .IP "$ctx\->digest" 4 | |
277 | .IX Item "$ctx->digest" | |
278 | Return the binary digest for the message. | |
279 | .Sp | |
280 | Note that the \f(CW\*(C`digest\*(C'\fR operation is effectively a destructive, | |
281 | read-once operation. Once it has been performed, the \f(CW$ctx\fR object is | |
282 | automatically \f(CW\*(C`reset\*(C'\fR and can be used to calculate another digest | |
283 | value. Call \f(CW$ctx\fR\->clone\->digest if you want to calculate the digest | |
284 | without reseting the digest state. | |
285 | .IP "$ctx\->hexdigest" 4 | |
286 | .IX Item "$ctx->hexdigest" | |
287 | Same as \f(CW$ctx\fR\->digest, but will return the digest in hexadecimal form. | |
288 | .IP "$ctx\->b64digest" 4 | |
289 | .IX Item "$ctx->b64digest" | |
290 | Same as \f(CW$ctx\fR\->digest, but will return the digest as a base64 encoded | |
291 | string. | |
292 | .SH "Digest speed" | |
293 | .IX Header "Digest speed" | |
294 | This table should give some indication on the relative speed of | |
295 | different algorithms. It is sorted by throughput based on a benchmark | |
296 | done with of some implementations of this \s-1API:\s0 | |
297 | .PP | |
298 | .Vb 1 | |
299 | \& Algorithm Size Implementation MB/s | |
300 | .Ve | |
301 | .PP | |
302 | .Vb 13 | |
303 | \& MD4 128 Digest::MD4 v1.3 165.0 | |
304 | \& MD5 128 Digest::MD5 v2.33 98.8 | |
305 | \& SHA-256 256 Digest::SHA2 v1.1.0 66.7 | |
306 | \& SHA-1 160 Digest::SHA v4.3.1 58.9 | |
307 | \& SHA-1 160 Digest::SHA1 v2.10 48.8 | |
308 | \& SHA-256 256 Digest::SHA v4.3.1 41.3 | |
309 | \& Haval-256 256 Digest::Haval256 v1.0.4 39.8 | |
310 | \& SHA-384 384 Digest::SHA2 v1.1.0 19.6 | |
311 | \& SHA-512 512 Digest::SHA2 v1.1.0 19.3 | |
312 | \& SHA-384 384 Digest::SHA v4.3.1 19.2 | |
313 | \& SHA-512 512 Digest::SHA v4.3.1 19.2 | |
314 | \& Whirlpool 512 Digest::Whirlpool v1.0.2 13.0 | |
315 | \& MD2 128 Digest::MD2 v2.03 9.5 | |
316 | .Ve | |
317 | .PP | |
318 | .Vb 5 | |
319 | \& Adler-32 32 Digest::Adler32 v0.03 1.3 | |
320 | \& CRC-16 16 Digest::CRC v0.05 1.1 | |
321 | \& CRC-32 32 Digest::CRC v0.05 1.1 | |
322 | \& MD5 128 Digest::Perl::MD5 v1.5 1.0 | |
323 | \& CRC-CCITT 16 Digest::CRC v0.05 0.8 | |
324 | .Ve | |
325 | .PP | |
326 | These numbers was achieved Apr 2004 with ActivePerl\-5.8.3 running | |
327 | under Linux on a P4 2.8 GHz \s-1CPU\s0. The last 5 entries differ by being | |
328 | pure perl implementations of the algorithms, which explains why they | |
329 | are so slow. | |
330 | .SH "SEE ALSO" | |
331 | .IX Header "SEE ALSO" | |
332 | Digest::Adler32, Digest::CRC, Digest::Haval256, | |
333 | Digest::HMAC, Digest::MD2, Digest::MD4, Digest::MD5, | |
334 | Digest::SHA, Digest::SHA1, Digest::SHA2, Digest::Whirlpool | |
335 | .PP | |
336 | New digest implementations should consider subclassing from Digest::base. | |
337 | .PP | |
338 | MIME::Base64 | |
339 | .SH "AUTHOR" | |
340 | .IX Header "AUTHOR" | |
341 | Gisle Aas <gisle@aas.no> | |
342 | .PP | |
343 | The \f(CW\*(C`Digest::\*(C'\fR interface is based on the interface originally | |
344 | developed by Neil Winton for his \f(CW\*(C`MD5\*(C'\fR module. | |
345 | .PP | |
346 | This library is free software; you can redistribute it and/or | |
347 | modify it under the same terms as Perl itself. | |
348 | .PP | |
349 | .Vb 2 | |
350 | \& Copyright 1998-2001,2003-2004 Gisle Aas. | |
351 | \& Copyright 1995-1996 Neil Winton. | |
352 | .Ve |