Serpent with 32 bytes key

[Antidote1911]

It's possible to use Serpent in CTR with a 32 bytes key ?
In this example decryption work with 16 bytes key but not 32.
(Same result if i try to encrypt with RustCrypto)

// does not ensure ciphertexts are authentic! Thus ciphertext integrity
// is not verified, which can lead to serious vulnerabilities!

use serpent::Serpent;
use serpent::cipher::{KeyIvInit, StreamCipher };
use serpent::cipher::generic_array::GenericArray;
use rand::{Rng, rngs::OsRng};

const KEYLEN:  usize = 32;
const NONCELEN:usize = 16;

type SerpentCtr = ctr::Ctr64BE<Serpent>;

fn main() {
    let plaintext=*b"super secret data to encrypt";
    let mut buf = plaintext.to_vec();

    let mut key_bytes = [0; KEYLEN];
    OsRng.fill(&mut key_bytes);

    let mut nonce_bytes = [0; NONCELEN];
    OsRng.fill(&mut nonce_bytes);

    let key = GenericArray::from_slice(&key_bytes);
    let iv = GenericArray::from_slice(&nonce_bytes);

    // encrypt with botan
    let engine = botan::Cipher::new("CTR-BE(Serpent)", botan::CipherDirection::Encrypt).unwrap();
    engine.set_key(&key).unwrap();
    engine.start(&iv).unwrap();
    let mut test = engine.finish(&mut buf).unwrap();

    // decrypt with rustcrypto
    let mut cipher = SerpentCtr::new(&key, &iv); // not work with 32 bytes key. left: `32`,right: `16`'
    cipher.apply_keystream(&mut test);

    assert_eq!(plaintext[..], test);
}

Thanks for RustCrypto, and for your work !

[tarcieri]

The current implementation only has support for 128-bit (16-byte) keys

[Antidote1911]

Thank you !