NAME

       Authen::Passphrase::Crypt16 - passphrases using Ultrix crypt16 algorithm

SYNOPSIS

               use Authen::Passphrase::Crypt16;

               $ppr = Authen::Passphrase::Crypt16->new(
                       salt_base64 => "qi",
                       hash_base64 => "8H8R7OM4xMUNMPuRAZxlY.");

               $ppr = Authen::Passphrase::Crypt16->new(
                       salt_random => 12,
                       passphrase => "passphrase");

               $salt = $ppr->salt;
               $salt_base64 = $ppr->salt_base64_2;
               $hash = $ppr->hash;
               $hash_base64 = $ppr->hash_base64;

               $ppr0 = $ppr->first_half;
               $ppr1 = $ppr->second_half;

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

DESCRIPTION

       An object of this class encapsulates a passphrase hashed using the "crypt16" hash function
       found in Ultrix and Tru64.  Do not confuse this with the "bigcrypt" found on HP-UX,
       Digital Unix, and OSF/1 (for which see Authen::Passphrase::BigCrypt).  This is a subclass
       of Authen::Passphrase, and this document assumes that the reader is familiar with the
       documentation for that class.

       This is a derivation of the original DES-based crypt function found on all Unices (see
       Authen::Passphrase::DESCrypt).  The first eight bytes of the passphrase are used as a DES
       key to encrypt the all-bits-zero block through 20 rounds of (12-bit) salted DES.  (The
       standard crypt function does this, but with 25 encryption rounds instead of 20.)  Then the
       next eight bytes, or the null string if the passphrase is eight bytes or shorter, are used
       as a DES key to encrypt the all-bits-zero block through 5 rounds of salted DES with the
       same salt.  The two eight-byte ciphertexts are concatenated to form the sixteen-byte hash.

       A password hash of this scheme is conventionally represented in ASCII as a 24-character
       string using a base 64 encoding.  The first two characters give the salt, the next eleven
       give the hash of the first half, and the last eleven give the hash of the second half.  A
       hash thus encoded is used as a crypt string, on those systems where the crypt16 algorithm
       is part of crypt(), but the syntax clashes with that of bigcrypt.  This module does not
       treat it as a crypt string syntax.

       Because the two halves of the passphrase are hashed separately, it is possible to
       manipulate (e.g., crack) a half hash in isolation.  See Authen::Passphrase::DESCrypt for
       handling of a single half.

       Warning: This is a fatally flawed design, often providing less security than the plain DES
       scheme alone.  Do not use seriously.

CONSTRUCTOR

       Authen::Passphrase::Crypt16->new(ATTR => VALUE, ...)
           Generates a new passphrase recogniser object using the crypt16 hash algorithm.  The
           following attributes may be given:

           salt
               The salt, as an integer in the range [0, 4096).

           salt_base64
               The salt, as a string of two base 64 digits.

           salt_random
               Causes salt to be generated randomly.  The value given for this attribute must be
               12, indicating generation of 12 bits of salt.  The source of randomness may be
               controlled by the facility described in Data::Entropy.

           hash
               The hash, as a string of 16 bytes.

           hash_base64
               The hash, as a string of 22 base 64 digits.

           passphrase
               A passphrase that will be accepted.

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

METHODS

       $ppr->salt
           Returns the salt, as a Perl integer.

       $ppr->salt_base64_2
           Returns the salt, as a string of two base 64 digits.

       $ppr->hash
           Returns the hash value, as a string of 16 bytes.

       $ppr->hash_base64
           Returns the hash value, as a string of 22 base 64 digits.  This is the concatenation
           of the base 64 encodings of the two hashes, rather than a base64 encoding of the
           combined hash.

       $ppr->first_half
           Returns the hash of the first half of the passphrase, as an
           Authen::Passphrase::DESCrypt passphrase recogniser.

       $ppr->second_half
           Returns the hash of the second half of the passphrase, as an
           Authen::Passphrase::DESCrypt passphrase recogniser.

       $ppr->match(PASSPHRASE)
           This method is part of the standard Authen::Passphrase interface.

SEE ALSO

       Authen::Passphrase, Authen::Passphrase::DESCrypt

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.