Authen::Passphrase::BigCrypt(3)

NAME
Authen::Passphrase::BigCrypt - passphrases using bigcrypt algorithm

SYNOPSIS
        use Authen::Passphrase::BigCrypt;

        $ppr = Authen::Passphrase::BigCrypt->new(
                salt_base64 => "qi",
                hash_base64 => "yh4XPJGsOZ2MEAyLkfWqeQ");

        $ppr = Authen::Passphrase::BigCrypt->new(
                salt_random => 12,
                passphrase => "passphrase");

        $salt = $ppr->salt;
        $salt_base64 = $ppr->salt_base64_2;
        $hash = $ppr->hash;
        $hash_base64 = $ppr->hash_base64;

        $pprs = $ppr->sections;

        if($ppr->match($passphrase)) { ...

DESCRIPTION
An object of this class encapsulates a passphrase hashed using the "bigcrypt" hash function found in HP-UX, Digital Unix, OSF/1, and some other flavours of Unix. Do not confuse this with the "crypt16" found on Ultrix and Tru64 (for which see Authen::Passphrase::Crypt16). This is a subclass of Authen::Passphrase, and this document assumes that the reader is familiar with the documentation for that class.

This is a derivation of the original DES-based crypt function found on all Unices (see Authen::Passphrase::DESCrypt). The first eight bytes of the passphrase are used as a DES key to encrypt the all-bits-zero block through 25 rounds of (12-bit) salted DES, just like the original crypt. Then, if the passphrase is longer than eight bytes, the next eight bytes are used as a DES key to encrypt the all-bits-zero block through 25 rounds of salted DES, using as salt the first 12 bits of the hash of the first section. Then, if the passphrase is longer than sixteen bytes, the next eight bytes are used, with salt consisting of the first 12 bits of the hash of the second section. This repeats until the entire passphrase has been used. The hashes of all the sections are concatenated to form the final hash.

A password hash of this scheme is conventionally represented in ASCII using the base 64 encoding of the underlying DES-based crypt function. The first two characters give the salt for the first section, the next eleven give the hash of the first section, the next eleven give the hash of the second section, and so on. A hash thus encoded is used as a crypt string, on those systems where the bigcrypt algorithm is part of crypt(), but the syntax clashes with that of crypt16. This module does not treat it as a crypt string syntax.

Because the sections of the passphrase are hashed separately, it is possible to manipulate (e.g., crack) a section hash in isolation. See Authen::Passphrase::DESCrypt for handling of a single section.

Warning: This is a fatally flawed design, often providing less security than the plain DES scheme alone. Do not use seriously.

CONSTRUCTOR

Authen::Passphrase::BigCrypt->new(ATTR => VALUE, ...)
    Generates a new passphrase recogniser object using the bigcrypt hash algorithm. The following attributes may be given:

    salt
        The salt for the first section, as an integer in the range [0, 4096).

    salt_base64
        The salt for the first section, as a string of two base 64 digits.

    salt_random
        Causes salt for the first section to be generated randomly. The value given for this attribute must be 12, indicating generation of 12 bits of salt. The source of randomness may be controlled by the facility described in Data::Entropy.

    hash
        The hash, as a string of bytes.

    hash_base64
        The hash, as a string of base 64 digits.

    passphrase
        A passphrase that will be accepted.

    The salt for the first section must be given, and either the hash or the passphrase.

METHODS

$ppr->salt
    Returns the salt for the first section, as a Perl integer.

$ppr->salt_base64_2
    Returns the salt for the first section, as a string of two base 64 digits.

$ppr->hash
    Returns the hash value, as a string of bytes.

$ppr->hash_base64
    Returns the hash value, as a string of base 64 digits. This is the concatenation of the base 64 encodings of the section hashes, rather than a base64 encoding of the combined hash.

$ppr->sections
    Returns a reference to an array of Authen::Passphrase::DESCrypt passphrase recognisers for the sections of the passphrase.

$ppr->match(PASSPHRASE)
    This method is part of the standard Authen::Passphrase interface.

SEE ALSO
Authen::Passphrase, Authen::Passphrase::DESCrypt

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.