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Crypt-ECB-2.05
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/ Crypt::ECB

NAME

Crypt::ECB - Use block ciphers using ECB mode

SYNOPSIS

Use Crypt::ECB OO style

use Crypt::ECB;

$ecb = Crypt::ECB->new;
$ecb->cipher('Blowfish');
$ecb->key('some_key'); 

$enc = $ecb->encrypt("Some data.");
print $ecb->decrypt($enc);

or use the function style interface

use Crypt::ECB qw(encrypt decrypt encrypt_hex decrypt_hex);

$ciphertext = encrypt($key, 'Blowfish', "Some data");
$plaintext  = decrypt($key, 'Blowfish', $ciphertext);

$hexcode = encrypt_hex($key, $cipher, $plaintext);
$plain   = decrypt_hex($key, $cipher, $hexcode);

DESCRIPTION

This module is a Perl-only implementation of the ECB mode. In combination with a block cipher such as Blowfish, DES, IDEA or Rijndael, you can encrypt and decrypt messages of arbitrarily long length. Though for security reasons other modes than ECB such as CBC should be preferred. See textbooks on cryptography if you want to know why.

The functionality of the module can be accessed via OO methods or via standard function calls. Remember that some block cipher module like for example Crypt::Blowfish has to be installed. The syntax of Crypt::ECB follows that of Crypt::CBC, so it can more or less be used as a drop-in replacement.

METHODS

new()

  $ecb = Crypt::ECB->new(
	-cipher    => $cipher,
	-key       => $key,
	-padding   => 'oneandzeroes',
	-keysize   => 8,  # use to override cipher's default
	-blocksize => 8,  # use to override cipher's default
  );

or

  $ecb = Crypt::ECB->new({
	cipher    => $cipher,
	key       => $key,
	padding   => 'oneandzeroes',
	keysize   => 8,  # use to override cipher's default
	blocksize => 8,  # use to override cipher's default
  });

or (only key and cipher can be passed this way)

$ecb = Crypt::ECB->new($key, 'Blowfish');
$ecb = Crypt::ECB->new($key);	# DES is assumed

The following options are recognized: cipher, key, keysize, blocksize and padding. Options can be passed like in Crypt::CBC. All options can be read and also be changed via corresponding methods afterwards.

If called without parameters you have to call at least key() and cipher() before you can start crypting.

cipher(), module(), key()

$ecb = Crypt::ECB->new;
$ecb->cipher('Blowfish');
$ecb->key('some_key');

print $ecb->cipher;	# Blowfish
print $ecb->module;	# Crypt::Blowfish
print $ecb->key;	# some_key

or

my $ecb  = Crypt::ECB->new;
my $xtea = Crypt::XTEA->new($key, 32, little_endian => 1);
$ecb->cipher($xtea);

cipher() sets the block cipher to be used. It tries to load the corresponding module. If an error occurs, it dies with some errmessage. Otherwise it returns the cipher name. Free packages available for Perl are for example Blowfish, DES, IDEA or Rijndael. If called without parameter it just returns the name of the cipher.

cipher() also accepts a pre-existing object from a suitable block cipher module. This is useful e.g. for cipher modules such as Crypt::XTEA which need additional parameters.

module() returns the perl package containing the block cipher which has been specified using cipher().

key() sets the key if given a parameter. It always returns the key. Note that most block ciphers require keys of definite length. For example DES expects an eight byte key.

keysize(), blocksize()

$ecb = Crypt::ECB->new;
$ecb->cipher('Blowfish');

$keysize   = $ecb->keysize;
$blocksize = $ecb->blocksize;

These methods can be used to retrieve keysize and blocksize as reported from the block cipher chosen. They can be used as well to override the values that are reported from the cipher module.

padding()

$ecb->padding('oneandzeroes');

my $custom_padding = sub { ... };
$ecb->padding($custom_padding);

padding() sets the way how data is padded up to a multiple of the cipher's blocksize. Until now the following methods are implemented: 'standard', 'zeroes', 'oneandzeroes', 'rijndael_compat', 'space', 'null' and 'none'. If the padding style is not set explicitly, 'standard' is used.

'standard' (default) (binary safe)
The PKCS#5 / PKCS#7 method (RFC 5652): Pads with the number of bytes
that should be truncated. So, if blocksize is 8, then "0A0B0C" will
be padded with five "05"s, resulting in "0A0B0C0505050505". If the
message is already a multiple of the cipher's block size, then another
whole block is appended.

'zeroes' (binary safe)
This is a variant of the standard method. It pads with null bytes, except
the last byte equals the number of padding bytes. So, if the blocksize is
8, then "0A0B0C" will be padded to "0A0B0C0000000005". If the message is
already a multiple of the cipher's block size, then another whole block
is appended.

'oneandzeroes' (binary safe)
Pads with "80" followed by as many "00"s as necessary to fill the block,
in other words a 1 bit followed by 0s. If the message already is a
multiple of the cipher's block size, then another whole block is
appended.

'rijndael_compat' (binary safe)
Similar to oneandzeroes, except that no padding is performed if the
message already is already a multiple of the cipher's block size. This is
provided for compatibility with Crypt::Rijndael.

'null'
Pads with as many null bytes as necessary to fill the block. If the
message is already a multiple of the cipher's block size, then another
whole block is appended.
ATTENTION: Can truncate more characters than it should (if the original
message ended with one or more null bytes).

'space'
Pads with as many space characters as necessary to fill the block.
If the message is already a multiple of the cipher's block size, unlike
the other methods NO block is appended.
ATTENTION: Can truncate more characters than it should (if the original
message ended with one or more space characters).

'none'
No padding added by Crypt::ECB. You then have to take care of correct
padding and truncating yourself.

You can also use a custom padding function. To do this, create a function that is called like:

$padded_block = function($block, $blocksize, $direction);

and tell Crypt::ECB to use your function:

$ecb->padding(\&function);

$block is the current block of data, $blocksize is the size to pad to, $direction is "e" for encrypting and "d" for decrypting, and $padded_block is the result after padding or truncation. When encrypting, the function should always return a string of $blocksize length, and when decrypting, it can expect the string coming in to be of that length.

start(), mode(), crypt(), finish()

$ecb->start('encrypt');
$enc .= $ecb->crypt($_) foreach (@lines);
$enc .= $ecb->finish;

$ecb->start('decrypt');
print $ecb->mode;

start() sets the crypting mode, checks if all required variables like key and cipher are set, then initializes the block cipher specified. Allowed parameters are any words starting either with 'e' or 'd'. The method returns the current mode.

mode() is called without parameters and just returns the current mode.

crypt() processes the data given as argument. If called without argument $_ is processed. The method returns the processed data. Cipher and key have to be set in order to be able to process data. If some of these are missing or start() was not called before, the method dies.

After having sent all data to be processed to crypt() you have to call finish() in order to flush data that's left in the buffer.

encrypt(), decrypt(), encrypt_hex(), decrypt_hex()

$enc = $ecb->encrypt($data);
print $ecb->decrypt($enc);

$hexenc = $ecb->encrypt_hex($data);
print $ecb->decrypt_hex($hexenc);

encrypt() and decrypt() are convenience methods which call start(), crypt() and finish() for you.

encrypt_hex() and decrypt_hex() are convenience functions that operate on ciphertext in a hexadecimal representation. These functions can be useful if, for example, you wish to place the encrypted information into an e-mail message, web page or URL.

FUNCTIONS

For convenience en- or decrypting can also be done by calling ordinary functions. The functions are: encrypt(), decrypt(), encrypt_hex(), decrypt_hex(). The module is smart enough to recognize whether these functions are called in an OO context or not.

encrypt(), decrypt(), encrypt_hex(), decrypt_hex()

$ciphertext = encrypt($key, $cipher, $plaintext, $padstyle);
$plaintext  = decrypt($key, $cipher, $ciphertext, $padstyle);

$ciphertext = encrypt_hex($key, $cipher, $plaintext, $padstyle);
$plaintext  = decrypt_hex($key, $cipher, $ciphertext, $padstyle);

encrypt() and decrypt() process the provided text and return either the corresponding ciphertext (encrypt) or plaintext (decrypt). Data and padstyle are optional. If the padding style is ommited, 'standard' is assumed. If data is omitted, $_ is used.

encrypt_hex() and decrypt_hex() operate on ciphertext in a hexadecimal representation. Otherwise usage is the same as for encrypt() and decrypt().

BUGS

None that I know of.

TODO

Implement 'random' padding, see http://www.di-mgt.com.au/cryptopad.html.

Convenience encrypt and decrypt functions utilizing base64 encoding could be added.

A taint check on the key like Crypt::CBC does could be added.

COPYING

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

AUTHOR

Christoph Appel (see ECB.pm for email address)

SEE ALSO

perl(1), Crypt::DES(3), Crypt::IDEA(3), Crypt::CBC(3)