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.