Crypt::Eksblowfish::FaUser(Contributed Perl DocumCrypt::Eksblowfish::Family(3)NAMECrypt::Eksblowfish::Family - Eksblowfish cipher family
SYNOPSIS
use Crypt::Eksblowfish::Family;
$family = Crypt::Eksblowfish::Family->new_family(8, $salt);
$cost = $family->cost;
$salt = $family->salt;
$block_size = $family->blocksize;
$key_size = $family->keysize;
$cipher = $family->new($key);
DESCRIPTION
An object of this class represents an Eksblowfish cipher family. It
contains the family parameters (cost and salt), and if combined with a
key it yields an encryption function. See Crypt::Eksblowfish for
discussion of the Eksblowfish algorithm.
It is intended that an object of this class can be used in situations
such as the "-cipher" parameter to "Crypt::CBC". Normally that
parameter is the name of a class, such as "Crypt::Rijndael", where the
class implements a block cipher algorithm. The class provides a "new"
constructor that accepts a key. In the case of Eksblowfish, the key
alone is not sufficient. An Eksblowfish family fills the role of block
cipher algorithm. Therefore a family object is used in place of a
class name, and it is the family object the provides the "new"
constructor.
Crypt::CBC
"Crypt::CBC" itself has a problem, with the result that this class can
no longer be used with it in the manner originally intended.
When this class was originally designed, it worked with "Crypt::CBC" as
described above: an object of this class would be accepted by
"Crypt::CBC" as a cipher algorithm, and "Crypt::CBC" would happily
supply it with a key and encrypt using the resulting cipher object.
"Crypt::CBC" didn't realise it was dealing with a family object,
however, and there was some risk that a future version might
accidentally squash the object into a string, which would be no use.
In the course of discussion about regularising the use of cipher family
objects, the author of "Crypt::CBC" got hold of the wrong end of the
stick, and ended up changing "Crypt::CBC" in a way that totally breaks
this usage, rather than putting it on a secure footing.
The present behaviour of "Crypt::CBC" is that if an object (rather than
a class name) is supplied as the "-cipher" parameter then it has a
completely different meaning from usual. In this case, the object
supplied is used as the keyed cipher, rather than as a cipher algorithm
which must be given a key. This bypasses all of "Crypt::CBC"'s usual
keying logic, which can hash and salt a passphrase to generate the key.
It is arguably a useful feature, but it's a gross abuse of the
"-cipher" parameter and a severe impediment to the use of family-keyed
cipher algorithms.
This class now provides a workaround. For the benefit of "Crypt::CBC",
and any other crypto plumbing that requires a keyable cipher algorithm
to look like a Perl class (rather than an object), a family object of
this class can in fact be reified as a class of its own. See the
method "as_class".
CONSTRUCTOR
Crypt::Eksblowfish::Family->new_family(COST, SALT)
Creates and returns an object representing the Eksblowfish cipher
family specified by the parameters. The SALT is a family key, and
must be exactly 16 octets. COST is an integer parameter
controlling the expense of keying: the number of operations in key
setup is proportional to 2^COST.
METHODS
$family->cost
Extracts and returns the cost parameter.
$family->salt
Extracts and returns the salt parameter.
$family->blocksize
Returns 8, indicating the Eksblowfish block size of 8 octets.
$family->keysize
Returns 0, indicating that the key size is variable. This
situation is handled specially by "Crypt::CBC".
$family->new(KEY)
Performs key setup on a new instance of the Eksblowfish algorithm,
returning the keyed state. The KEY may be any length from 1 octet
to 72 octets inclusive. The object returned is of class
"Crypt::Eksblowfish"; see Crypt::Eksblowfish for the encryption and
decryption methods.
Note that this method is called on a family object, not on the
class "Crypt::Eksblowfish::Family".
$family->encrypt
This method nominally exists, to satisfy "Crypt::CBC". It can't
really be used: it doesn't make any sense.
$family->as_class
Generates and returns (the name of) a Perl class that behaves as a
keyable cipher algorithm identical to this Eksblowfish cipher
family. The same methods that can be called as instance methods on
$family can be called as class methods on the generated class.
You should prefer to use the family object directly wherever you
can. Aside from being a silly indirection, the classes generated
by this method cannot be garbage-collected. This method exists
only to cater to "Crypt::CBC", which requires a keyable cipher
algorithm to look like a Perl class, and won't operate correctly on
one that looks like an object.
SEE ALSO
Crypt::CBC, Crypt::Eksblowfish
AUTHOR
Andrew Main (Zefram) <zefram@fysh.org>
COPYRIGHT
Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Andrew Main (Zefram)
<zefram@fysh.org>
LICENSE
This module is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
perl v5.14.1 2011-06-21 Crypt::Eksblowfish::Family(3)
