man Authen::DecHpwd (3): 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.

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 <[email protected]> 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) <[email protected]> created a new "Authen::DecHpwd" based on the more developed C code presently used, and added ancillary functions.

COPYRIGHT

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