/ 
Twofish-1.0
/ Crypt::Twofish

NAME

Crypt::Twofish - Perl extension for Twofish. Twofish is a 128-bit block cipher.

SYNOPSIS

use Crypt::Twofish; 

$ciphertext = Encipher($key,$keylength,$plaintext); 

$decryptedtext = Decipher($key,$keylength,$ciphertext,$cipherlength);
                                                                           
$lasterror = LastError();  

CheckTwofish();

DESCRIPTION

This module is a perl extension for the Twofish encryption algorithm. 
The following are the four functions that this module supports:

1. Encipher
2. Decipher
3. LastError
4. CheckTwofish

Encipher takes the key, the key length and the message to be encrypted as parameters and returns the ciphertext. This is a variation from the actual Twofish algorithm which only accepts keys of length 128 (16 bytes), 194 (24 bytes) or 256(32 bytes). What this algorithm does is, if the key length is not equal to 128, 194 or 256 bits, and less than 256, it appends the key to itself until the key length becomes equal to 256(32 bytes). If the key length is more than 32 bytes then only the first 32 bytes are considered as the key. Basically, you can use any key you want and the module would do the rest for you. You would typically call encipher as:

$ciphertext = Encipher($key,$keylength,$plaintext);

Note: Remember to pass the key length parameter in bytes.

Decipher takes the key, keylength, ciphertext and the length of ciphertext
as parameters and returns the plain text. Even Decipher does the same kind
of key repitition as Encipher. Here it is important to remember that you 
have to use the same key with which you have encrypted, otherwise you get
garbled output. Decipher can typically be called as:

 $decryptedtext = Decipher($key,$keylength,$ciphertext,$cipherlength);

 $cipherlength is the length of the ciphertext, which is a multiple of 16
 (the block size). It can be useful for decrypting substrings. Once again
 pass the key length in bytes.

 
LastError is a very useful function when something goes wrong with Encipher 
or Decipher. It returns the  last error  that was encountered. It does not 
take any arguements and can be simply called as:

 $lasterror = LastError();

 CheckTwofish is

INSTALLATION

You can install this module by using the following commands:

perl Makefile.PL
make
make test
make install

AUTHOR

Nishant Kakani, nishantkakani@hotmail.com

I would like to thank Xenoscience Inc. and Counterpane Systems, without 
whose help I wouldn't have written this module. 
=head1 SEE ALSO
More about the Twofish algorithm can be found at the following site: 

http://www.counterpane.com/twofish.html