Crypt::Eksblowfish::UkUserwContributed Perl Crypt::Eksblowfish::Uklblowfish(3)NAMECrypt::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
Crypt::Eksblowfish::Blowfish
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.
perl v5.18.22014-05-13Crypt::Eksblowfish::Uklblowfish(3)