NAME
Crypt::Eksblowfish::Uklblowfish - Blowfish cipher with unrestricted key length
SYNOPSIS
use Crypt::Eksblowfish::Uklblowfish;
$block_size = Crypt::Eksblowfish::Uklblowfish->blocksize;
$key_size = Crypt::Eksblowfish::Uklblowfish->keysize;
$cipher = Crypt::Eksblowfish::Uklblowfish->new($key);
$block_size = $cipher->blocksize;
$ciphertext = $cipher->encrypt($plaintext);
$plaintext = $cipher->decrypt($ciphertext);
$p_array = $cipher->p_array;
$s_boxes = $cipher->s_boxes;
if($cipher->is_weak) { ...DESCRIPTION
An object of this type encapsulates a keyed instance of the Blowfish block cipher, ready to encrypt and decrypt. However, if you're looking for an implementation of Blowfish you most likely want Crypt::Eksblowfish::Blowfish. This class differs from the standard Blowfish in that it accepts some keys that Blowfish officially does not permit.
Blowfish is a symmetric cipher algorithm designed by Bruce Schneier in 1993. It operates on 64-bit blocks, and takes a variable-length key. Officially the key can vary from 32 bits (4 octets) to 448 bits (56 octets) in increments of 8 bits (1 octet). In fact the algorithm can easily operate on a key of any number of octets from 1 (8 bits) to 72 (576 bits). Some implementations don't enforce the official key length limits, and so for compatibility it is sometimes necessary to handle a Blowfish key of a prohibited length. That is what this class is for. The "Ukl" in the name stands for "unrestricted key length".
Using a very short key is generally a bad idea because there aren't very many keys of that length and so it's easy for an attacker to try them all. The official 32-bit minimum for Blowfish was already far too short for serious security at the time that Blowfish was designed. (A machine to crack 56-bit DES keys by brute force in a few days each was publicly built only five years later.) Do not base your security on the secrecy of a short key.
Using overlong keys has more interesting effects, which depend on internal features of Blowfish. When the key exceeds 64 octets (512 bits), varying key bits past that length results in subkeys which have predictable relationships. There is also some possibility of equivalent keys when the keys exceed 64 octets and differ only in the first 8 octets (64 bits). These phenomena have not been extensively studied in the open literature, so it is difficult to judge the degree of cryptographic weakness that results from them. It is clear that beyond some length Blowfish keys do not have as much strength as their length would suggest, and it is possible that overlong keys have specific weaknesses that render them weaker than shorter keys. If choosing a key for security, it is advised to stay within the official length limit of 56 octets.
In summary: using Blowfish keys of officially-unsupported lengths causes security problems. If you are using Blowfish for security, and have the choice, use a key of an officially-supported length (and a standard implementation such as Crypt::Eksblowfish::Blowfish). Use out-of-range key lengths (and this class) only for compatibility or cryptanalytic reasons.
CLASS METHODS
- Crypt::Eksblowfish::Uklblowfish->blocksize
-
Returns 8, indicating the Blowfish block size of 8 octets. This method may be called on either the class or an instance.
- Crypt::Eksblowfish::Uklblowfish->keysize
-
Returns 0, indicating that the key size is variable. This situation is handled specially by
Crypt::CBC.
CONSTRUCTOR
- Crypt::Eksblowfish::Uklblowfish->new(KEY)
-
Performs key setup on a new instance of the Blowfish algorithm, returning the keyed state. The KEY may be any length from 1 octet to 72 octets inclusive.
METHODS
- $cipher->blocksize
-
Returns 8, indicating the Blowfish block size of 8 octets. This method may be called on either the class or an instance.
- $cipher->encrypt(PLAINTEXT)
-
PLAINTEXT must be exactly eight octets. The block is encrypted, and the ciphertext is returned.
- $cipher->decrypt(CIPHERTEXT)
-
CIPHERTEXT must be exactly eight octets. The block is decrypted, and the plaintext is returned.
- $cipher->p_array
- $cipher->s_boxes
-
These methods extract the subkeys from the keyed cipher. This is not required in ordinary operation. See the superclass Crypt::Eksblowfish::Subkeyed for details.
- $cipher->is_weak
-
This method checks whether the cipher has been keyed with a weak key. It may be desired to avoid using weak keys. See the superclass Crypt::Eksblowfish::Subkeyed for details.
This method does not detect any cryptographic weaknesses that might result from the related-key properties and other features of overlong keys.
SEE ALSO
AUTHOR
Eksblowfish guts originally by Solar Designer (solar at openwall.com).
Modifications and Perl interface by Andrew Main (Zefram) <zefram@fysh.org>.
COPYRIGHT
Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Andrew Main (Zefram) <zefram@fysh.org>
The original Eksblowfish code (in the form of crypt()) from which this module is derived is in the public domain. It may be found at http://www.openwall.com/crypt/.
LICENSE
This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.