NAME

       Crypt::UnixCrypt_XS - perl xs interface for a portable traditional crypt function.

SYNOPSIS

         use Crypt::UnixCrypt_XS qw/crypt/;
         my $hashed = crypt( $password, $salt );

         use Crypt::UnixCrypt_XS qw/crypt_rounds fold_password
             base64_to_block block_to_base64
             base64_to_int24 int24_to_base64
             base64_to_int12 int12_to_base64/;
         $block = crypt_rounds( $password, $nrounds, $saltnum, $block );
         $password = fold_password( $password );
         $block = base64_to_block( $base64 );
         $base64 = block_to_base64( $block );
         $saltnum = base64_to_int24( $base64 );
         $base64 = int24_to_base64( $saltnum );
         $saltnum = base64_to_int12( $base64 );
         $base64 = int12_to_base64( $saltnum );

DESCRIPTION

       This module implements the DES-based Unix crypt function.  For those who need to construct
       non-standard variants of crypt, the various building blocks used in crypt are also
       supplied separately.

FUNCTIONS

       crypt( PASSWORD, SALT )
           This is the conventional crypt interface.  PASSWORD and SALT are both strings.  The
           password will be hashed, in a manner determined by the salt, and a string is returned
           containing the salt and hash.  The salt is at the beginning of the returned string,
           and only the beginning of the salt string is examined, so it is acceptable to use a
           string returned by crypt as a salt argument.  Three different types of hashing may
           occur:

           If the salt is an empty string, then the password is ignored and an empty string is
           returned.  The empty salt/hash string is thus used to not require a password.

           If the salt string starts with two base 64 digits (from the set [./0-9A-Za-z]), then
           the password is hashed using the traditional DES-based algorithm.  The salt is used to
           modify the DES algorithm in one of 4096 different ways.  The first eight characters of
           the password are used as a DES key, to encrypt a block of zeroes through 25 iterations
           of the modified DES.  The block output by the final iteration is the hash, and it is
           returned in base 64 (as eleven digits).

           If the salt string starts with an underscore character and then eight base 64 digits
           then the password is hashed using the extended DES-based algorithm from BSDi.  The
           first four base 64 digits specify how many encryption rounds are to be performed.  The
           next four base 64 digits are used to modify the DES algorithm in one of 16777216
           different ways.  If the password is longer than eight characters, it is hashed down to
           eight characters before being used as a key, so all characters of the password are
           significant.

       crypt_rounds( PASSWORD, NROUNDS, SALTNUM, BLOCK )
           This is the core of the DES-based crypt algorithm, exposed here to allow variant hash
           functions to be built.  PASSWORD is a string; its first eight characters are used as a
           DES key.  SALTNUM is an integer; its low 24 bits are used to modify the DES algorithm.
           BLOCK must be a string exactly eight bytes long.  The data block is passed through
           NROUNDS iterations of the modified DES, and the final output block (also a string of
           exactly eight bytes) is returned.

       fold_password( PASSWORD )
           This is the pre-hashing algorithm used in the extended DES algorithm to fold a long
           password to the size of a DES key.  It takes a password of any length, and returns a
           password of eight characters which is completely equivalent in the extended DES
           algorithm.  Note: the password returned may contain NUL characters.  The functions in
           this module correctly handle NULs in password strings, but a normal C library crypt
           cannot.  If you need the short password to contain no NULs, perform the substitution
           "s/\0/\x80/g": the top bit of each password character is ignored, so the result is
           equivalent.

       base64_to_block( BASE64 )
           This converts a data block from a string of eleven base 64 digits to a raw string of
           eight bytes.

       block_to_base64( BLOCK )
           This converts a data block from a raw string of eight bytes to a string of eleven base
           64 digits.

       base64_to_int24( BASE64 )
           This converts a 24-bit integer from a string of four base 64 digits to a Perl integer.

       int24_to_base64( VALUE )
           This converts a 24-bit integer from a Perl integer to a string of four base 64 digits.

       base64_to_int12( BASE64 )
           This converts a 12-bit integer from a string of two base 64 digits to a Perl integer.

       int12_to_base64( VALUE )
           This converts a 12-bit integer from a Perl integer to a string of two base 64 digits.

   EXPORT
       None by default.

RATIONALE

       Crypt::UnixCrypt_XS provide a fast portable crypt function. Perl's internal crypt is not
       present at every system. Perl calls the crypt function of the system's C library. This may
       lead to trouble if the system's crypt presents different results for the same key and
       salt, but different processid's. Crypt::UnixCrypt is the cure here, but it is to slow. On
       my computer Crypt::UnixCrypt_XS is about 800 times faster than Crypt::UnixCrypt.

SEE ALSO

       crypt(3), Crypt::UnixCrypt

AUTHOR

       Boris Zentner, <bzm@2bz.de>, the original C source code was written by Eric Young,
       eay@psych.uq.oz.au.

CREDITS

       Fixes, Bug Reports, Docs have been generously provided by:

         Andrew Main (Zefram) <zefram@fysh.org>
         Guenter Knauf
       Thanks!

COPYRIGHT AND LICENSE

       Copyright (C) 2004, 2005, 2006, 2007 by Boris Zentner

       This library is free software; you can redistribute it and/or modify it under the same
       terms as Perl itself, either Perl version 5.8.3 or, at your option, any later version of
       Perl 5 you may have available.