Authen::DecHpwd(3pm)					User Contributed Perl Documentation				      Authen::DecHpwd(3pm)

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 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.

perl v5.14.2							    2011-11-15						      Authen::DecHpwd(3pm)