8-bit cfb-mode support (CFB8), versus only 128-bit (CFB128) about stream-ciphers HOT 6 CLOSED

Sorry for the delay!

I've published cfb8 crate. Feel free to open new issues if you'll have any problems with RustCrypto crates or will need additional primitives!

from stream-ciphers.

Found these test vectors: https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38a.pdf F.3.8 CFB8-AES128.Decrypt (8-bit CFB)

Example in Python:

from Crypto.Cipher import AES

key="2b7e151628aed2a6abf7158809cf4f3c".decode("hex")
iv="000102030405060708090a0b0c0d0e0f".decode("hex")

cipher=AES.new(key, AES.MODE_CFB, iv, segment_size=8)
decrypted=cipher.decrypt("3b79424c9c0dd436bace9e0ed4586a4f32b9".decode("hex"))
print "decrypted = ",decrypted.encode("hex")
print "expected  = ","6bc1bee22e409f96e93d7e117393172aae2d"

Rust:

use aes::Aes128;
use cfb_mode::Cfb;

type Aes128Cfb = Cfb<Aes128>;

fn main() {
    let key = hex!("2b7e151628aed2a6abf7158809cf4f3c");
    let iv = hex!("000102030405060708090a0b0c0d0e0f");
    let mut cipher = Aes128Cfb::new_var(&key, &iv).unwrap();

    let mut data = hex!("3b79424c9c0dd436bace9e0ed4586a4f32b9");
    cipher.decrypt(&mut data);
    println!("decrypted = {:?}", data);

    let expected = hex!("6bc1bee22e409f96e93d7e117393172aae2d");
    println!("expected  = {:?}", expected);
}

output:

decrypted = [107, 135, 37, 128, 5, 96, 230, 128, 96, 199, 169, 231, 79, 247, 134, 47, 174, 70]
expected  = [107, 193, 190, 226, 46, 64, 159, 150, 233, 61, 126, 17, 115, 147, 23, 42, 174, 45]

from stream-ciphers.

cfb-mode currently implements CFB which XORs with full blocks (i.e. for AES it's CFB128). It's successfully passes CFB128 tests from the recommendations. Do you need CFB8 for compatibility reasons? Because they only differ in the rate of error recovery, while performance is significantly worse.

It shouldn't be that difficult to add CFB8, but I will be able to work on it probably only on this weekend,

from stream-ciphers.

Yes I'm porting a client where the server uses CFB8 for some reason. Appreciate your work on this

from stream-ciphers.

How would this be implemented? Should Cfb be generic over the block size (Cfb<8>, Cfb<128>, can you do that in Rust?) Or separate classes? (Cfb8, Cfb128, etc.)

from stream-ciphers.

Thanks! Ported my code over to use cfb8, works great.

from stream-ciphers.