NAME

Crypt::CFB - Encrypt Data in Cipher Feedback Mode

SYNOPSIS

        use Crypt::CFB;

        my $cipher = new Crypt::CFB $key, 'Crypt::Rijndael';

        ## Or:
        my $iv = ''; map { $iv .= chr(rand(256)) } (0..16);
        my $cipher = new Crypt::CFB $key, 'Crypt::Rijndael', $iv;

        my $ciphertext = $cipher->encrypt($plaintext);
        my $plaintext = $cipher->decrypt($ciphertext);

        my $cipher2 = new Crypt::CFB $key, 'Digest::MD5';

        $ciphertext = $cipher->encrypt($plaintext);
        $plaintext = $cipher->decrypt($ciphertext);

DESCRIPTION

Generic CFB implementation in pure Perl. The Cipher Feedback Mode module constructs a stream cipher from a block cipher or cryptographic hash funtion and returns it as an object. Any block cipher in the Crypt:: class can be used, as long as it supports the blocksize and keysize methods. Any hash function in the Digest:: class can be used, as long as it supports the add method.

METHODS

$cipher = new Crypt::CFB $key, $algorithm, $optional_iv

Constructs a CFB object. If $algorithm is a block cipher, then $key should be of the correct size for that cipher. In most cases you can inquire the block cipher module by invoking the keysize method. If $algorithm is a hash function (Digest::), then $key can be of any size. The optional IV can be used to further seed the crypto algorithm. If no IV is given, a string of zeroes is used.

$ciphertext = $cipher->encrypt $plaintext

Encrypts $plaintext. The input is XORed with the keystream generated from the internal state of the CFB object and that state is updated with the output. $plaintext can be of any length.

$cipher->reset

Resets the internal state. Remember to do that before decrypting, if you use the same object.

$plaintext = $cipher->decrypt $ciphertext

Decrypts $ciphertext.

BUGS

This is awfully slow. Some classes in Digest:: do not provide the add method, so they will fail. The implementation is a little baroque.

AUTHOR

Matthias Bauer <matthiasb@acm.org>

CHANGES

Added the use of an IV.

AUTHOR

Kees Jan Hermans <kees@phoezo.com>