Provided by: libauthen-passphrase-perl_0.008-3_all 
NAME
Authen::Passphrase::BlowfishCrypt - passphrases using the Blowfish-based Unix crypt()
SYNOPSIS
use Authen::Passphrase::BlowfishCrypt;
$ppr = Authen::Passphrase::BlowfishCrypt->new(
cost => 8,
salt => "sodium__chloride",
hash_base64 => "BPZijhMHLvPeNMHd6XwZyNamOXVBTPi");
$ppr = Authen::Passphrase::BlowfishCrypt->new(
cost => 8, salt_random => 1,
passphrase => "passphrase");
$ppr = Authen::Passphrase::BlowfishCrypt->from_crypt(
'$2a$08$a07iYVTrVz7hYEvtakjiXOB'.
'PZijhMHLvPeNMHd6XwZyNamOXVBTPi');
$ppr = Authen::Passphrase::BlowfishCrypt->from_rfc2307(
'{CRYPT}$2a$08$a07iYVTrVz7hYEvtakjiXOB'.
'PZijhMHLvPeNMHd6XwZyNamOXVBTPi');
$key_nul = $ppr->key_nul;
$cost = $ppr->cost;
$cost = $ppr->keying_nrounds_log2;
$salt = $ppr->salt;
$salt_base64 = $ppr->salt_base64;
$hash = $ppr->hash;
$hash_base64 = $ppr->hash_base64;
if($ppr->match($passphrase)) { ...
$passwd = $ppr->as_crypt;
$userPassword = $ppr->as_rfc2307;
DESCRIPTION
An object of this class encapsulates a passphrase hashed using the Blowfish-based Unix
crypt() hash function, known as "bcrypt". This is a subclass of Authen::Passphrase, and
this document assumes that the reader is familiar with the documentation for that class.
The crypt() function in a modern Unix actually supports several different passphrase
schemes. This class is concerned only with one particular scheme, a Blowfish-based
algorithm designed by Niels Provos and David Mazieres for OpenBSD. To handle the whole
range of passphrase schemes supported by the modern crypt(), see the from_crypt
constructor and the as_crypt method in Authen::Passphrase.
The Blowfish-based crypt() scheme uses a variant of Blowfish called "Eksblowfish", for
"expensive key schedule Blowfish". It has the cryptographic strength of Blowfish, and a
very slow key setup phase to resist brute-force attacks. There is a "cost" parameter to
the scheme: the length of key setup is proportional to 2^cost. There is a 128-bit salt.
Up to 72 characters of the passphrase will be used; any more will be ignored.
The cost, salt, and passphrase are all used to (very slowly) key Eksblowfish. Once key
setup is done, the string "OrpheanBeholderScryDoubt" (three Blowfish blocks long) is
encrypted 64 times in ECB mode. The final byte of the ciphertext is then dropped,
yielding a 23-byte hash.
In the crypt() function the salt and hash are represented in ASCII using a base 64
encoding. The base 64 digits are ".", "/", "A" to "Z", "a" to "z", "0" to "9" (in that
order). The 16-byte salt is represented as 22 base 64 digits, and the 23-byte hash as 31
base 64 digits.
This algorithm is intended for situations where the efficiency of a brute force attack is
a concern. It is suitable for use in new applications where this requirement exists. If
that is not a concern, and it suffices to merely make brute force the most efficient
attack, see Authen::Passphrase::SaltedDigest for more efficient hash algorithms.
Choice of the cost parameter is critical, due to the need to trade off expense of brute-
force attack against speed of legitimate passphrase verification. A traditional target is
that verification should take about one second on widely-available hardware. (Algorithms
that are concerned about brute force speed but lack a cost parameter have often aimed for
this, with respect to hardware available at the time of the algorithm's introduction.) As
of 2011, this is achieved with a cost parameter around 14.
CONSTRUCTORS
Authen::Passphrase::BlowfishCrypt->new(ATTR => VALUE, ...)
Generates a new passphrase recogniser object using the Blowfish-based crypt()
algorithm. The following attributes may be given:
key_nul
Truth value indicating whether to append a NUL to the passphrase before using it
as a key. The algorithm as originally devised does not do this, but it was later
modified to do it. The version that does append NUL is to be preferred. Default
true.
cost
Base-two logarithm of the number of keying rounds to perform.
keying_nrounds_log2
Synonym for cost.
salt
The salt, as a 16-byte string.
salt_base64
The salt, as a string of 22 base 64 digits.
salt_random
Causes salt to be generated randomly. The value given for this attribute is
ignored. The source of randomness may be controlled by the facility described in
Data::Entropy.
hash
The hash, as a 23-byte string.
hash_base64
The hash, as a string of 31 base 64 digits.
passphrase
A passphrase that will be accepted.
The cost and salt must be given, and either the hash or the passphrase.
Authen::Passphrase::BlowfishCrypt->from_crypt(PASSWD)
Generates a new passphrase recogniser object using the Blowfish-based crypt()
algorithm, from a crypt string. The crypt string must start with "$2$" for the
version that does not append NUL to the key, or "$2a$" for the version that does. The
next two characters must be decimal digits giving the cost parameter. This must be
followed by "$", 22 base 64 digits giving the salt, and finally 31 base 64 digits
giving the hash.
Authen::Passphrase::BlowfishCrypt->from_rfc2307(USERPASSWORD)
Generates a new passphrase recogniser object using the Blowfish-based crypt()
algorithm, from an RFC 2307 string. The string must consist of "{CRYPT}" (case
insensitive) followed by an acceptable crypt string.
METHODS
$ppr->key_nul
Returns a truth value indicating whether a NUL will be appended to the passphrase
before using it as a key.
$ppr->cost
Returns the base-two logarithm of the number of keying rounds that will be performed.
$ppr->keying_nrounds_log2
Synonym for "cost".
$ppr->salt
Returns the salt, as a string of sixteen bytes.
$ppr->salt_base64
Returns the salt, as a string of 22 base 64 digits.
$ppr->hash
Returns the hash value, as a string of 23 bytes.
$ppr->hash_base64
Returns the hash value, as a string of 31 base 64 digits.
$ppr->match(PASSPHRASE)
$ppr->as_crypt
$ppr->as_rfc2307
These methods are part of the standard Authen::Passphrase interface.
SEE ALSO
Authen::Passphrase, Crypt::Eksblowfish::Bcrypt
AUTHOR
Andrew Main (Zefram) <zefram@fysh.org>
COPYRIGHT
Copyright (C) 2006, 2007, 2009, 2010, 2012 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.