NAME

       Authen::DecHpwd - DEC VMS password hashing

SYNOPSIS

               use Authen::DecHpwd qw(
                       UAI_C_AD_II UAI_C_PURDY UAI_C_PURDY_V UAI_C_PURDY_S
                       lgi_hpwd
               );

               $hash = lgi_hpwd("JRANDOM", "PASSWORD", UAI_C_PURDY_S, 1234);

               use Authen::DecHpwd qw(vms_username vms_password);

               $username = vms_username($username);
               $password = vms_password($password);

DESCRIPTION

       This module implements the "SYS$HASH_PASSWORD" password hashing function from VMS (also known as
       "LGI$HPWD"), and some associated VMS username and password handling functions.

       The password hashing function is implemented in XS, with a hideously slow pure Perl backup version for
       systems that can't handle XS.

FUNCTIONS

       UAI_C_AD_II
       UAI_C_PURDY
       UAI_C_PURDY_V
       UAI_C_PURDY_S
           These constants are used to identify the four password hashing algorithms used by VMS.  They are the
           "UAI$C_" constants in VMS.

           "UAI_C_AD_II" refers to a 32-bit CRC algorithm.  The CRC polynomial used is the IEEE CRC-32
           polynomial, as used in Ethernet, and in this context is known as "AUTODIN-II".  The hash is merely
           the CRC of the password.

           "UAI_C_PURDY", "UAI_C_PURDY_V", and "UAI_C_PURDY_S" refer to successive refinements of an algorithm
           based on Purdy polynomials.  All of these algorithms use the salt and username parameters as salt,
           use the whole password, and return an eight-byte (64-bit) hash.  The main part of the algorithm, the
           Purdy polynomial, is identical in all three.  They differ in the pre-hashing, particularly in the
           treatment of the username parameter.

           In "UAI_C_PURDY" the username is truncated or space-padded to 12 characters before being hashed in.
           "UAI_C_PURDY_V" accepts a variable-length username.  "UAI_C_PURDY_S" accepts a variable-length
           username and also includes the password length in the hash.  "UAI_C_PURDY_S" also does some extra bit
           rotations when hashing in the username and password strings, in order to avoid aliasing.

       lgi_hpwd(USERNAME, PASSWORD, ALGORITHM, SALT)
           This is the "SYS$HASH_PASSWORD" function from VMS (also known as "LGI$HPWD"), but with the parameters
           in a different order.  It hashes the PASSWORD string in a manner determined by the other parameters,
           and returns the hash as a string of bytes.

           ALGORITHM determines which hashing algorithm will be used.  It must be the value of one of the
           algorithm constants supplied by this module (see above).

           SALT must be an integer in the range [0, 2^16).  It modifies the hashing so that the same password
           does not always produce the same hash.

           USERNAME is a string that is used as more salt.  In VMS it is the username of the account to which
           the password controls access.

           VMS usernames and passwords are constrained in character set and length, and are case-insensitive.
           This function does not enforce these restrictions, nor perform canonicalisation.  If restrictions and
           canonicalisation are desired then they must be applied separately.  The functions "vms_username" and
           "vms_password" described below may be useful.

       vms_username(USERNAME)
           Checks whether the USERNAME string matches VMS username syntax, and canonicalises it.  VMS username
           syntax is 1 to 31 characters from case-insensitive alphanumerics, "_", and "$".  If the string has
           correct username syntax then the username is returned in canonical form (uppercase).  If the string
           is not a username then "undef" is returned.

       vms_password(PASSWORD)
           Checks whether the PASSWORD string is an acceptable VMS password, and canonicalises it.  VMS password
           syntax is 1 to 32 characters from case-insensitive alphanumerics, "_", and "$".  If the string is an
           acceptable password then the password is returned in canonical form (uppercase).  If the string is
           not an acceptable password then "undef" is returned.

SEE ALSO

       VMS::User

AUTHOR

       The original C implementation of "LGI$HPWD" was written by Shawn Clifford.  The code has since been
       developed by Davide Casale, Mario Ambrogetti, Terence Lee, Jean-loup Gailly, Solar Designer, and Andrew
       Main (Zefram).

       Mike McCauley <mikem@open.com.au> created the first version of "Authen::DecHpwd", establishing the Perl
       interface.  This was based on Shawn Clifford's code without the later developments.

       Andrew Main (Zefram) <zefram@fysh.org> created a new "Authen::DecHpwd" based on the more developed C code
       presently used, and added ancillary functions.

COPYRIGHT

       Copyright (C) 2002 Jean-loup Gailly <http://gailly.net>

       Based in part on code from John the Ripper, Copyright (C) 1996-2002 Solar Designer

       Copyright (C) 2006, 2007, 2009, 2010, 2011, 2017 Andrew Main (Zefram) <zefram@fysh.org>

LICENSE

       This module is free software; you can redistribute it and/or modify it under the terms of the GNU General
       Public License as published by the Free Software Foundation; either version 2 of the License, or (at your
       option) any later version.