Regression: SS_RC4_MD5's salt_len has changed

[spacemeowx2]

In 0.3.x, the iv_len of SS_RC4_MD5 is changed from 16 to 0.

https://github.com/shadowsocks/shadowsocks-crypto/blob/main/src/v1/streamcipher/rc4_md5.rs#L45

https://github.com/shadowsocks/shadowsocks-crypto/blob/v0.2.5/src/v1/streamcipher/rc4_md5.rs#L24

[spacemeowx2]

const KEY: &'static [u8] = b"1234123412341234";
const EMPTY_IV: &'static [u8] = b"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
const EMPTY: &'static [u8] = b"";
const MSG: &'static [u8] = b"Hello, world!";

fn old_enc() -> Vec<u8> {
    let mut cipher =
        old_crypto::v1::Cipher::new(old_crypto::v1::CipherKind::SS_RC4_MD5, KEY, EMPTY_IV);

    let mut helloworld = MSG.to_vec();

    cipher.encrypt_packet(&mut helloworld);

    helloworld
}

fn main() {
    let mut helloworld = old_enc();
    let mut cipher =
        old_crypto::v1::Cipher::new(old_crypto::v1::CipherKind::SS_RC4_MD5, KEY, EMPTY_IV);

    assert!(cipher.decrypt_packet(&mut helloworld));
    assert_eq!(helloworld, MSG);

    let mut helloworld = old_enc();
    let mut cipher =
        fix_crypto::v1::Cipher::new(fix_crypto::v1::CipherKind::SS_RC4_MD5, KEY, EMPTY_IV);

    assert!(cipher.decrypt_packet(&mut helloworld));
    assert_eq!(helloworld, MSG);

    println!("{:?}", helloworld);

    let mut helloworld = old_enc();
    // NOTE that the IV len is zero, so it's impossible to decrypt
    let mut cipher =
        new_crypto::v1::Cipher::new(new_crypto::v1::CipherKind::SS_RC4_MD5, KEY, EMPTY);

    assert!(cipher.decrypt_packet(&mut helloworld));
    // assert failed here
    assert_eq!(helloworld, MSG);
}

https://github.com/spacemeowx2/bug-crypto

[spacemeowx2]

I think a regression test needs to be done for each CipherKind.