Authen::Passphrase::VMSPurdy(3)

NAME
Authen::Passphrase::VMSPurdy - passphrases with the VMS Purdy polynomial system

SYNOPSIS
        use Authen::Passphrase::VMSPurdy;

        $ppr = Authen::Passphrase::VMSPurdy->new(
                        username => "jrandom", salt => 25362,
                        hash_hex => "832a0c270179584a");

        $ppr = Authen::Passphrase::VMSPurdy->new(
                        username => "jrandom", salt_random => 1,
                        passphrase => "passphrase");

        $ppr = Authen::Passphrase::VMSPurdy->from_crypt(
                '$VMS3$1263832A0C270179584AJRANDOM');

        $ppr = Authen::Passphrase::VMSPurdy->from_rfc2307(
                '{CRYPT}$VMS3$1263832A0C270179584AJRANDOM');

        $algorithm = $ppr->algorithm;
        $username = $ppr->username;
        $salt = $ppr->salt;
        $hash = $ppr->hash;
        $hash_hex = $ppr->hash_hex;

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

        $passwd = $ppr->as_crypt;
        $userPassword = $ppr->as_rfc2307;

DESCRIPTION
An object of this class encapsulates a passphrase hashed using one of the Purdy polynomial hash functions used in VMS. This is a subclass of Authen::Passphrase, and this document assumes that the reader is familiar with the documentation for that class.

The core of the Purdy polynomial hashing algorithm transforms one 64-bit number into another 64-bit number. It was developed by George B. Purdy, and described in the paper "A High Security Log-in Procedure" which can be found at <http://portal.acm.org/citation.cfm?id=361089&dl=GUIDE&coll=ACM&CFID=15151515&CFTOKEN=6184618>.

For practical use in passphrase hashing, the Purdy polynomial must be augmented by a procedure to turn a variable-length passphrase into the initial 64-bit number to be hashed. In VMS this pre-hashing phase also incorporates the username of the account to which access is being controlled, in order to prevent identical passphrases yielding identical hashes. This is a form of salting. Another salt parameter, a 16-bit integer, is also included, this one going under the name "salt".

There are three variants of the pre-hashing algorithm. The original version, known as "PURDY" and used during field testing of VMS 2.0, truncates or space-pads the username to a fixed length. The second version, known as "PURDY_V" and used from VMS 2.0 up to (but not including) VMS 5.4, properly handles the variable-length nature of the username. The third version, known as "PURDY_S" and used from VMS 5.4 onwards, performs some extra bit rotations to avoid aliasing problems when pre-hashing long strings. All three versions are supported by this module.

VMS heavily restricts the composition of both usernames and passphrases. They may only contain alphanumerics, "$", and "_". Case is insignificant. Usernames must be between 1 and 31 characters long, and passphrases must be between 1 and 32 characters long. This module enforces these rules. An invalid passphrase is never accepted as matching.

CONSTRUCTORS

Authen::Passphrase::VMSPurdy->new(ATTR => VALUE, ...)
    Generates a new passphrase recogniser object using the VMS Purdy polynomial algorithm family. The following attributes may be given:

    algorithm
        A string indicating which variant of the algorithm is to be used. Valid values are "PURDY" (the original), "PURDY_V" (modified to use full length of the username), and "PURDY_S" (extra rotations to avoid aliasing when processing long strings). Default "PURDY_S".

    username
        A string to be used as the `username' salt parameter. It is limited to VMS username syntax.

    salt
        The salt, as an integer in the range [0, 65536).

    salt_hex
        The salt, as a string of four hexadecimal digits. The first two digits must give the least-significant byte and the last two give the most-significant byte, with most-significant nybble first within each byte.

    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 string of eight bytes.

    hash_hex
        The hash, as a string of 16 hexadecimal digits.

    passphrase
        A passphrase that will be accepted. It is limited to VMS passphrase syntax.

    The username and salt must be given, and either the hash or the passphrase.

Authen::Passphrase::VMSPurdy->from_crypt(PASSWD)
    Generates a new passphrase recogniser object using the VMS Purdy polynomial algorithm family, from a crypt string. The string must consist of an algorithm identifier, the salt in hexadecimal, the hash in hexadecimal, then the username. The salt must be given as four hexadecimal digits, the first two giving the least-significant byte and the last two giving the most-significant byte, with most-significant nybble first within each byte. The algorithm identifier must be "$VMS1$" for "PURDY", "$VMS2$" for "PURDY_V", or "$VMS3$" for "PURDY_S". The whole crypt string must be uppercase.

Authen::Passphrase::VMSPurdy->from_rfc2307(USERPASSWORD)
    Generates a new passphrase recogniser object using the VMS Purdy polynomial algorithm family, from an RFC 2307 string. The string must consist of "{CRYPT}" (case insensitive) followed by an acceptable crypt string.

METHODS

$ppr->algorithm
    Returns the algorithm variant identifier string. It may be "PURDY" (the original), "PURDY_V" (modified to use full length of the username), and "PURDY_S" (extra rotations to avoid aliasing when processing long strings).

$ppr->username
    Returns the username string. All alphabetic characters in it are uppercase, which is the canonical form.

$ppr->salt
    Returns the salt, as an integer.

$ppr->salt_hex
    Returns the salt, as a string of four hexadecimal digits. The first two digits give the least-significant byte and the last two give the most-significant byte, with most-significant nybble first within each byte.

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

$ppr->hash_hex
    Returns the hash value, as a string of 16 uppercase hexadecimal digits.

$ppr->match(PASSPHRASE)
$ppr->as_crypt
$ppr->as_rfc2307
    These methods are part of the standard Authen::Passphrase interface.

SEE ALSO
Authen::DecHpwd, Authen::Passphrase

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.