Crypt::Ctr - Encrypt Data in Counter Mode
use Crypt::Ctr;
my $cipher = new Crypt::Ctr $key, 'Crypt::Rijndael';
my $ciphertext = $cipher->encrypt($plaintext);
my $plaintext = $cipher->decrypt($ciphertext);
my $cipher2 = new Crypt::Ctr $key, 'Digest::MD5';
$ciphertext = $cipher->encrypt($plaintext);
$plaintext = $cipher->decrypt($ciphertext);
Generic Counter Mode implementation in pure Perl. The Counter 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.
Counter mode produces the keystream independent from the input. Be sure not to
re-use keys in Counter mode. As with Cipher Feedback mode, one should use
Counter mode inside authenticated channels, e.g. HMAC.
- "$cipher = new Crypt::Ctr $key, $algorithm"
- Constructs a Crypt::Ctr 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, then
$key can be of any size.
- "$ciphertext = $cipher->encrypt $plaintext"
- Encrypts $plaintext. The input is XORed with the
keystream generated from the internal state of the Ctr 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.
This is awfully slow. Some classes in
"Digest::" do not provide the
"add" method, so they will fail. The
internal counter is a Perl integer. This could possibly lead to strange errors
when encrypting more than "POSIX::LONG_MAX"
bytes and decrypting it on a different architecture.
Matthias Bauer <matthiasb@acm.org>