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Man Pages


Manual Reference Pages  -  CRYPT::TWOFISH2 (3)

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NAME

Crypt::Twofish2 - Crypt::CBC compliant Twofish encryption module

CONTENTS

SYNOPSIS



 use Crypt::Twofish2;

 # keysize() is 32, but 24 and 16 are also possible
 # blocksize() is 16

 $cipher = new Crypt::Twofish2 "a" x 32, Crypt::Twofish2::MODE_CBC;

 $crypted = $cipher->encrypt($plaintext);
 # - OR -
 $plaintext = $cipher->decrypt($crypted);



DESCRIPTION

This module implements the twofish cipher in a less braindamaged (read: slow and ugly) way than the existing Crypt::Twofish module.

Although it is Crypt::CBC compliant you usually gain nothing by using that module (except generality, which is often a good thing), since Crypt::Twofish2 can work in either ECB or CBC mode itself.
keysize Returns the keysize, which is 32 (bytes). The Twofish2 cipher actually supports keylengths of 16, 24 or 32 bytes, but there is no way to communicate this to Crypt::CBC.
blocksize The blocksize for Twofish2 is 16 bytes (128 bits), which is somewhat unique. It is also the reason I need this module myself ;)
$cipher = new $key [, $mode] Create a new Crypt::Twofish2 cipher object with the given key (which must be 128, 192 or 256 bits long). The additional $mode argument is the encryption mode, either MODE_ECB (electronic cookbook mode, the default), MODE_CBC (cipher block chaining, the same that Crypt::CBC does) or MODE_CFB1 (1-bit cipher feedback mode).

ECB mode is very insecure (read a book on cryptography if you don’t know why!), so you should probably use CBC mode. CFB1 mode is not tested and is most probably broken, so do not try to use it.

In ECB mode you can use the same cipher object to encrypt and decrypt data. However, every change of direction causes an internal reordering of key data, which is quite slow, so if you want ECB mode and encryption/decryption at the same time you should create two seperate Crypt::Twofish2 objects with the same key.

In CBC mode you have to use seperate objects for encryption/decryption in any case.

The MODE_*-constants are not exported by this module, so you must specify them as Crypt::Twofish2::MODE_CBC etc. (sorry for that).

$cipher->encrypt($data) Encrypt data. The size of $data must be a multiple of blocksize (16 bytes), otherwise this function will croak. Apart from that, it can be of (almost) any length.
$cipher->decrypt($data) The pendant to encrypt in that it decrypts data again.

SEE ALSO

Crypt::CBC, Crypt::Twofish.

BUGS

Should EXPORT or EXPORT_OK the MODE constants.

There should be a way to access initial IV contents :(

Although I tried to make the original twofish code portable, I can’t say how much I did succeed. The code tries to be portable itself, and I hope I got the endianness issues right. The code is also copyright Counterpane Systems, no license accompanied it, so using it might actually be illegal ;)

I also cannot guarantee for security, but the module is used quite a bit, so there are no obvious bugs left.

AUTHOR



 Marc Lehmann <schmorp@schmorp.de>
 http://home.schmorp.de/

 The actual twofish encryption is written in horribly microsoftish looking
 almost ansi-c by Doug Whiting.



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