[bug] The MinSize specified for ChaCha20Poly1305 in crypto is incorrect

[DCNick3]

(identified by @Erigara)

When doing impl Encryptor for ChaCha20Poly1305 in iroha_crypto, we currently specify U36 as a MinSize (which is used to error out if a message too short is passed to the decryptor).

This, however, is incorrect. In actuality, the shortest possible message we can have is 28 bytes. Here's a breakdown:

• ChaChaPoly1305 outputs a len(input) + 16 ciphertext (same length as input + 128-bit tag from Poly1305); see https://www.rfc-editor.org/rfc/rfc8439#section-2.8
• Encryptor prepends it with a 96-bit (12 bytes) nonce

0 + 16 + 12 = 28

This results in iroha crashing when receiving short messages.

test:

#[test]
fn test() {
    let cipher = ChaCha20Poly1305::new(&ChaCha20Poly1305::key_gen().unwrap());
    let aad = b"Iroha2 AAD".to_vec();
    // Single byte as for scale enums
    let message = b"".to_vec();
    let ciphertext = cipher.encrypt_easy(&aad, &message).unwrap();
    let decrypted_message = cipher.decrypt_easy(&aad, &ciphertext).unwrap();
    assert_eq!(message, decrypted_message);
}

[DCNick3]

Fixed in #4396