1CBC(3) User Contributed Perl Documentation CBC(3)
2
6 Crypt::CBC - Encrypt Data with Cipher Block Chaining Mode
7
9 use Crypt::CBC;
10 $cipher = Crypt::CBC->new( -key => 'my secret key',
11 -cipher => 'Blowfish'
12 );
13 $ciphertext = $cipher->encrypt("This data is hush hush");
15 $plaintext = $cipher->decrypt($ciphertext);
16 $cipher->start('encrypting');
18 open(F,"./BIG_FILE");
19 while (read(F,$buffer,1024)) {
20 print $cipher->crypt($buffer);
21 }
22 print $cipher->finish;
23 # do-it-yourself mode -- specify key, initialization vector yourself
25 $key = Crypt::CBC->random_bytes(8); # assuming a 8-byte block cipher
26 $iv = Crypt::CBC->random_bytes(8);
27 $cipher = Crypt::CBC->new(-literal_key => 1,
28 -key => $key,
29 -iv => $iv,
30 -header => 'none');
31 $ciphertext = $cipher->encrypt("This data is hush hush");
33 $plaintext = $cipher->decrypt($ciphertext);
34 # RANDOMIV-compatible mode
36 $cipher = Crypt::CBC->new(-key => 'Super Secret!'
37 -header => 'randomiv');
38
40 This module is a Perl-only implementation of the cryptographic cipher
41 block chaining mode (CBC). In combination with a block cipher such as
42 DES or IDEA, you can encrypt and decrypt messages of arbitrarily long
43 length. The encrypted messages are compatible with the encryption
44 format used by the OpenSSL package.
45 To use this module, you will first create a Crypt::CBC cipher object
47 with new(). At the time of cipher creation, you specify an encryption
48 key to use and, optionally, a block encryption algorithm. You will
49 then call the start() method to initialize the encryption or decryption
50 process, crypt() to encrypt or decrypt one or more blocks of data, and
51 lastly finish(), to pad and encrypt the final block. For your
52 convenience, you can call the encrypt() and decrypt() methods to
53 operate on a whole data value at once.
54 new()
56 $cipher = Crypt::CBC->new( -key => 'my secret key',
57 -cipher => 'Blowfish',
58 );
59 # or (for compatibility with versions prior to 2.13)
61 $cipher = Crypt::CBC->new( {
62 key => 'my secret key',
63 cipher => 'Blowfish'
64 }
65 );
66 # or (for compatibility with versions prior to 2.0)
69 $cipher = new Crypt::CBC('my secret key' => 'Blowfish');
70 The new() method creates a new Crypt::CBC object. It accepts a list of
72 -argument => value pairs selected from the following list:
73 Argument Description
75 -------- -----------
76 -key The encryption/decryption key (required)
78 -cipher The cipher algorithm (defaults to Crypt::DES), or
80 a preexisting cipher object.
81 -salt Enables OpenSSL-compatibility. If equal to a value
83 of "1" then causes a random salt to be generated
84 and used to derive the encryption key and IV. Other
85 true values are taken to be the literal salt.
86 -iv The initialization vector (IV)
88 -header What type of header to prepend to ciphertext. One of
90 'salt' -- use OpenSSL-compatible salted header
91 'randomiv' -- Randomiv-compatible "RandomIV" header
92 'none' -- prepend no header at all
93 -padding The padding method, one of "standard" (default),
95 "space", "oneandzeroes", "rijndael_compat",
96 "null", or "none" (default "standard").
97 -literal_key If true, the key provided by "key" is used directly
99 for encryption/decryption. Otherwise the actual
100 key used will be a hash of the provided key.
101 (default false)
102 -pcbc Whether to use the PCBC chaining algorithm rather than
104 the standard CBC algorithm (default false).
105 -keysize Force the cipher keysize to the indicated number of bytes.
107 -blocksize Force the cipher blocksize to the indicated number of bytes.
109 -insecure_legacy_decrypt
111 Allow decryption of data encrypted using the "RandomIV" header
112 produced by pre-2.17 versions of Crypt::CBC.
113 -add_header [deprecated; use -header instread]
115 Whether to add the salt and IV to the header of the output
116 cipher text.
117 -regenerate_key [deprecated; use literal_key instead]
119 Whether to use a hash of the provided key to generate
120 the actual encryption key (default true)
121 -prepend_iv [deprecated; use add_header instead]
123 Whether to prepend the IV to the beginning of the
124 encrypted stream (default true)
125 Crypt::CBC requires three pieces of information to do its job. First it
127 needs the name of the block cipher algorithm that will encrypt or
128 decrypt the data in blocks of fixed length known as the cipher's
129 "blocksize." Second, it needs an encryption/decryption key to pass to
130 the block cipher. Third, it needs an initialization vector (IV) that
131 will be used to propagate information from one encrypted block to the
132 next. Both the key and the IV must be exactly the same length as the
133 chosen cipher's blocksize.
134 Crypt::CBC can derive the key and the IV from a passphrase that you
136 provide, or can let you specify the true key and IV manually. In
137 addition, you have the option of embedding enough information to
138 regenerate the IV in a short header that is emitted at the start of the
139 encrypted stream, or outputting a headerless encryption stream. In the
140 first case, Crypt::CBC will be able to decrypt the stream given just
141 the original key or passphrase. In the second case, you will have to
142 provide the original IV as well as the key/passphrase.
143 The -cipher option specifies which block cipher algorithm to use to
145 encode each section of the message. This argument is optional and will
146 default to the quick-but-not-very-secure DES algorithm unless specified
147 otherwise. You may use any compatible block encryption algorithm that
148 you have installed. Currently, this includes Crypt::DES,
149 Crypt::DES_EDE3, Crypt::IDEA, Crypt::Blowfish, Crypt::CAST5 and
150 Crypt::Rijndael. You may refer to them using their full names
151 ("Crypt::IDEA") or in abbreviated form ("IDEA").
152 Instead of passing the name of a cipher class, you may pass an already-
154 created block cipher object. This allows you to take advantage of
155 cipher algorithms that have parameterized new() methods, such as
156 Crypt::Eksblowfish:
157 my $eksblowfish = Crypt::Eksblowfish->new(8,$salt,$key);
159 my $cbc = Crypt::CBC->new(-cipher=>$eksblowfish);
160 The -key argument provides either a passphrase to use to generate the
162 encryption key, or the literal value of the block cipher key. If used
163 in passphrase mode (which is the default), -key can be any number of
164 characters; the actual key will be derived by passing the passphrase
165 through a series of MD5 hash operations. To take full advantage of a
166 given block cipher, the length of the passphrase should be at least
167 equal to the cipher's blocksize. To skip this hashing operation and
168 specify the key directly, pass a true value to the -literal_key option.
169 In this case, you should choose a key of length exactly equal to the
170 cipher's key length. You should also specify the IV yourself and a
171 -header mode of 'none'.
172 If you pass an existing Crypt::* object to new(), then the -key
174 argument is ignored and the module will generate a warning.
175 The -header argument specifies what type of header, if any, to prepend
177 to the beginning of the encrypted data stream. The header allows
178 Crypt::CBC to regenerate the original IV and correctly decrypt the data
179 without your having to provide the same IV used to encrypt the data.
180 Valid values for the -header are:
181 "salt" -- Combine the passphrase with an 8-byte random value to
183 generate both the block cipher key and the IV from the
184 provided passphrase. The salt will be appended to the
185 beginning of the data stream allowing decryption to
186 regenerate both the key and IV given the correct passphrase.
187 This method is compatible with current versions of OpenSSL.
188 "randomiv" -- Generate the block cipher key from the passphrase, and
190 choose a random 8-byte value to use as the IV. The IV will
191 be prepended to the data stream. This method is compatible
192 with ciphertext produced by versions of the library prior to
193 2.17, but is incompatible with block ciphers that have non
194 8-byte block sizes, such as Rijndael. Crypt::CBC will exit
195 with a fatal error if you try to use this header mode with a
196 non 8-byte cipher.
197 "none" -- Do not generate a header. To decrypt a stream encrypted
199 in this way, you will have to provide the original IV
200 manually.
201 The "salt" header is now the default as of Crypt::CBC version 2.17. In
203 all earlier versions "randomiv" was the default.
204 When using a "salt" header, you may specify your own value of the salt,
206 by passing the desired 8-byte salt to the -salt argument. Otherwise,
207 the module will generate a random salt for you. Crypt::CBC will
208 generate a fatal error if you specify a salt value that isn't exactly 8
209 bytes long. For backward compatibility reasons, passing a value of "1"
210 will generate a random salt, the same as if no -salt argument was
211 provided.
212 The -padding argument controls how the last few bytes of the encrypted
214 stream are dealt with when they not an exact multiple of the cipher
215 block length. The default is "standard", the method specified in
216 PKCS#5.
217 The -pcbc argument, if true, activates a modified chaining mode known
219 as PCBC. It provides better error propagation characteristics than the
220 default CBC encryption and is required for authenticating to Kerberos4
221 systems (see RFC 2222).
222 The -keysize and -blocksize arguments can be used to force the cipher's
224 keysize and/or blocksize. This is only currently useful for the
225 Crypt::Blowfish module, which accepts a variable length keysize. If
226 -keysize is not specified, then Crypt::CBC will use the maximum length
227 Blowfish key size of 56 bytes (448 bits). The Openssl library defaults
228 to 16 byte Blowfish key sizes, so for compatibility with Openssl you
229 may wish to set -keysize=>16. There are currently no Crypt::* modules
230 that have variable block sizes, but an option to change the block size
231 is provided just in case.
232 For compatibility with earlier versions of this module, you can provide
234 new() with a hashref containing key/value pairs. The key names are the
235 same as the arguments described earlier, but without the initial
236 hyphen. You may also call new() with one or two positional arguments,
237 in which case the first argument is taken to be the key and the second
238 to be the optional block cipher algorithm.
239 IMPORTANT NOTE: Versions of this module prior to 2.17 were incorrectly
241 using 8-byte IVs when generating the "randomiv" style of header, even
242 when the chosen cipher's blocksize was greater than 8 bytes. This
243 primarily affects the Rijndael algorithm. Such encrypted data streams
244 were not secure. From versions 2.17 onward, Crypt::CBC will refuse to
245 encrypt or decrypt using the "randomiv" header and non-8 byte block
246 ciphers. To decrypt legacy data encrypted with earlier versions of the
247 module, you can override the check using the -insecure_legacy_decrypt
248 option. It is not possible to override encryption. Please use the
249 default "salt" header style, or no headers at all.
250 start()
252 $cipher->start('encrypting');
253 $cipher->start('decrypting');
254 The start() method prepares the cipher for a series of encryption or
256 decryption steps, resetting the internal state of the cipher if
257 necessary. You must provide a string indicating whether you wish to
258 encrypt or decrypt. "E" or any word that begins with an "e" indicates
259 encryption. "D" or any word that begins with a "d" indicates
260 decryption.
261 crypt()
263 $ciphertext = $cipher->crypt($plaintext);
264 After calling start(), you should call crypt() as many times as
266 necessary to encrypt the desired data.
267 finish()
269 $ciphertext = $cipher->finish();
270 The CBC algorithm must buffer data blocks internally until they are
272 even multiples of the encryption algorithm's blocksize (typically 8
273 bytes). After the last call to crypt() you should call finish(). This
274 flushes the internal buffer and returns any leftover ciphertext.
275 In a typical application you will read the plaintext from a file or
277 input stream and write the result to standard output in a loop that
278 might look like this:
279 $cipher = new Crypt::CBC('hey jude!');
281 $cipher->start('encrypting');
282 print $cipher->crypt($_) while <>;
283 print $cipher->finish();
284 encrypt()
286 $ciphertext = $cipher->encrypt($plaintext)
287 This convenience function runs the entire sequence of start(), crypt()
289 and finish() for you, processing the provided plaintext and returning
290 the corresponding ciphertext.
291 decrypt()
293 $plaintext = $cipher->decrypt($ciphertext)
294 This convenience function runs the entire sequence of start(), crypt()
296 and finish() for you, processing the provided ciphertext and returning
297 the corresponding plaintext.
298 encrypt_hex(), decrypt_hex()
300 $ciphertext = $cipher->encrypt_hex($plaintext)
301 $plaintext = $cipher->decrypt_hex($ciphertext)
302 These are convenience functions that operate on ciphertext in a
304 hexadecimal representation. encrypt_hex($plaintext) is exactly
305 equivalent to unpack('H*',encrypt($plaintext)). These functions can be
306 useful if, for example, you wish to place the encrypted in an email
307 message.
308 get_initialization_vector()
310 $iv = $cipher->get_initialization_vector()
311 This function will return the IV used in encryption and or decryption.
313 The IV is not guaranteed to be set when encrypting until start() is
314 called, and when decrypting until crypt() is called the first time.
315 Unless the IV was manually specified in the new() call, the IV will
316 change with every complete encryption operation.
317 set_initialization_vector()
319 $cipher->set_initialization_vector('76543210')
320 This function sets the IV used in encryption and/or decryption. This
322 function may be useful if the IV is not contained within the ciphertext
323 string being decrypted, or if a particular IV is desired for
324 encryption. Note that the IV must match the chosen cipher's blocksize
325 bytes in length.
326 iv()
328 $iv = $cipher->iv();
329 $cipher->iv($new_iv);
330 As above, but using a single method call.
332 key()
334 $key = $cipher->key();
335 $cipher->key($new_key);
336 Get or set the block cipher key used for encryption/decryption. When
338 encrypting, the key is not guaranteed to exist until start() is called,
339 and when decrypting, the key is not guaranteed to exist until after the
340 first call to crypt(). The key must match the length required by the
341 underlying block cipher.
342 When salted headers are used, the block cipher key will change after
344 each complete sequence of encryption operations.
345 salt()
347 $salt = $cipher->salt();
348 $cipher->salt($new_salt);
349 Get or set the salt used for deriving the encryption key and IV when in
351 OpenSSL compatibility mode.
352 passphrase()
354 $passphrase = $cipher->passphrase();
355 $cipher->passphrase($new_passphrase);
356 This gets or sets the value of the key passed to new() when literal_key
358 is false.
359 $data = random_bytes($numbytes)
361 Return $numbytes worth of random data. On systems that support the
362 "/dev/urandom" device file, this data will be read from the device.
363 Otherwise, it will be generated by repeated calls to the Perl rand()
364 function.
365 cipher(), padding(), keysize(), blocksize(), pcbc()
367 These read-only methods return the identity of the chosen block cipher
368 algorithm, padding method, key and block size of the chosen block
369 cipher, and whether PCBC chaining is in effect.
370 Padding methods
372 Use the 'padding' option to change the padding method.
373 When the last block of plaintext is shorter than the block size, it
375 must be padded. Padding methods include: "standard" (i.e., PKCS#5),
376 "oneandzeroes", "space", "rijndael_compat", "null", and "none".
377 standard: (default) Binary safe
379 pads with the number of bytes that should be truncated. So, if
380 blocksize is 8, then "0A0B0C" will be padded with "05", resulting
381 in "0A0B0C0505050505". If the final block is a full block of 8
382 bytes, then a whole block of "0808080808080808" is appended.
383 oneandzeroes: Binary safe
385 pads with "80" followed by as many "00" necessary to fill the
386 block. If the last block is a full block and blocksize is 8, a
387 block of "8000000000000000" will be appended.
388 rijndael_compat: Binary safe, with caveats
390 similar to oneandzeroes, except that no padding is performed if
391 the last block is a full block. This is provided for
392 compatibility with Crypt::Rijndael only and can only be used
393 with messages that are a multiple of the Rijndael blocksize
394 of 16 bytes.
395 null: text only
397 pads with as many "00" necessary to fill the block. If the last
398 block is a full block and blocksize is 8, a block of
399 "0000000000000000" will be appended.
400 space: text only
402 same as "null", but with "20".
403 none:
405 no padding added. Useful for special-purpose applications where
406 you wish to add custom padding to the message.
407 Both the standard and oneandzeroes paddings are binary safe. The space
409 and null paddings are recommended only for text data. Which type of
410 padding you use depends on whether you wish to communicate with an
411 external (non Crypt::CBC library). If this is the case, use whatever
412 padding method is compatible.
413 You can also pass in a custom padding function. To do this, create a
415 function that takes the arguments:
416 $padded_block = function($block,$blocksize,$direction);
418 where $block is the current block of data, $blocksize is the size to
420 pad it to, $direction is "e" for encrypting and "d" for decrypting, and
421 $padded_block is the result after padding or depadding.
422 When encrypting, the function should always return a string of
424 <blocksize> length, and when decrypting, can expect the string coming
425 in to always be that length. See _standard_padding(), _space_padding(),
426 _null_padding(), or _oneandzeroes_padding() in the source for examples.
427 Standard and oneandzeroes padding are recommended, as both space and
429 null padding can potentially truncate more characters than they should.
430
432 Two examples, des.pl and idea.pl can be found in the eg/ subdirectory
433 of the Crypt-CBC distribution. These implement command-line DES and
434 IDEA encryption algorithms.
435
437 The encryption and decryption process is about a tenth the speed of the
438 equivalent SSLeay programs (compiled C). This could be improved by
439 implementing this module in C. It may also be worthwhile to optimize
440 the DES and IDEA block algorithms further.
441
443 Please report them.
444
446 Lincoln Stein, lstein@cshl.org
447 This module is distributed under the ARTISTIC LICENSE using the same
449 terms as Perl itself.
450
452 perl(1), Crypt::DES(3), Crypt::IDEA(3), rfc2898 (PKCS#5)
453perl v5.30.0 2019-07-26 CBC(3)