#! /bin/perl
#############################################################################
#
#                 NOTE: This file under revision control using RCS
#                       Any changes made without RCS will be lost
#
#              $Source: U:\\mhansen\\bin\\RCS\\pass_gen,v $
#            $Revision: 1.2 $
#                $Date: 2002-11-09 17:22:45-06 $
#              $Author: mhansen $
#              $Locker: mhansen $
#               $State: Exp $
#
#
#              Purpose: Generates random password using with alternating
#                       consonants and vowels to make the passwords easier to 
#                       remember. Also include one numeric character randomly
#                       positioned in the password.
#
#          Description: The built-in Perl rand() function uses the standard C
#                       library routine rand (3) to generate pseudo-random
#                       numbers. Some implementations of the rand function
#                       return only 16-bit random numbers or have algorithmic
#                       weaknesses and may not be sufficiently random. A further
#                       weakness is the source of the seed for the generator.
#                       The default seed is based on the time and process ID,
#                       not a particularly large range of possible seeds.
#
#                       This implementation uses /dev/urandom, a kernel module
#                       available on most UNIX systems as the source of random
#                       data. The /dev/urandom driver gathers environmental
#                       noise from various non-deterministic sources within the
#                       operating system environment.
#
#                       /dev/urandom like /dev/random but considerably faster.
#                       The /dev/urandom driver does not wait for the entropy-
#                       pool to recharge and immediately returns as many bytes 
#                       as requested. For password generation this is 
#                       acceptable. Applications that requires a high quality of 
#                       randomness should use /dev/random instead.
#
#
#           Directions: Usage: pass_gen
#                       return generated password to STDOUT
#
#     Default Location: /share/local/bin/pass_gen
#
#           Invoked by: user
#
#           Depends on: Random device driver such as /dev/urandom
#
#       Copyright (C) 1999  Marc Hansen
#
#       This program is free software; you can redistribute it and/or
#       modify it under the terms of version 2 of the GNU General Public
#       License as published by the Free Software Foundation available at:
#       http://http://www.gnu.org/copyleft/gpl.html
#
#       This program is distributed in the hope that it will be useful,
#       but WITHOUT ANY WARRANTY; without even the implied warranty of
#       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#       GNU General Public License for more details.
#
#############################################################################
#
#
#       REVISION HISTORY:
#
#       $Log: pass_gen,v $
#       Revision 1.2  2002-11-09 17:22:45-06  mhansen
#       Changed from /dev/random to /dev/urandom
#
#       Revision 1.1  1999-02-05 15:10:49-06  mhansen
#       Added numeric character
#
#       Revision 1.0  1999-01-29 17:07:13-06  mhansen
#       Initial revision
#
#
#

#
# Constants
#
$SIZE=8;                                                # Size of password

$DEVRANDOM="/dev/urandom";                              # Random byte device
                                                        #   For higher quality 
                                                        #   randomness set to 
                                                        #   /dev/random
                                                        
@vwl = qw(a e i o u);                                   # 5 vowels
@con = qw(b c d f g h j k l m n p r s t v w y z);       # 19 consonants
@num = qw(2 3 4 5 6 7 8 9);                             # 8 numbers


#
# Get random bytes from /dev/urandom
# Put $SIZE+1 random bytes in array @rand
#
open RND, "$DEVRANDOM";
read (RND, $rand, $SIZE+1);
@rand  = split //, $rand;
 
 
 
#
# Loop for each character in password
#   Convert random byte to number 0-255 with ord()
#   Scale random byte to required range with % modulus operator
#   Use last random byte to choose position of numeric component
#
for ($i=0; $i<$SIZE; $i++) {
    if    ($i==ord(@rand[$SIZE])%$SIZE) {print @num[ord(@rand[$i])%8 ]}
    elsif ($i%2)                        {print @vwl[ord(@rand[$i])%5 ]}
    else                                {print @con[ord(@rand[$i])%19]}
}
print "\n";

exit 0;

__END__