Crate eme2_extended 

Generic implementation of EME2 mode extended for arbitrary block ciphers.

Mode functionality is accessed using traits from re-exported cipher crate. EME2-extended (ECB-Mask-ECB) is a wide-block cipher mode of operation that acts as a Strong Pseudorandom Permutation (SPRP).

Unlike standard EME2 which is limited to 128-bit block ciphers, this crate utilizes an EmePoly trait to provide compile-time verified Galois Field polynomials for 128-bit, 256-bit, 512-bit, and 1024-bit block sizes, securely supporting ciphers like Threefish.

⚠️ Security Warning: Hazmat!

This crate does not ensure ciphertexts are authentic! Thus ciphertext integrity is not verified, which can lead to serious vulnerabilities! It is highly recommended to use EME2 in combination with a strong MAC to provide robust authenticated encryption.

Migrating from Stream Ciphers (e.g., CTR Mode)

Because eme2-extended strictly implements RustCrypto’s KeyIvInit traits, instantiating the cipher is a 1:1 drop-in replacement for stream ciphers like ctr. However, execution differs:

• Stream Ciphers (CTR): Encryption and decryption are mathematically identical, so they use the StreamCipher trait and expose .apply_keystream(&mut data).
• Wide-Block Ciphers (EME2): Encryption and decryption are asymmetric. Thus, EME2 does not implement StreamCipher and instead exposes explicit .encrypt(&mut data) and .decrypt(&mut data) methods.

Examples

Encryption with a tweak

use aes::cipher::KeyIvInit;
use eme2_extended::Eme2;

type Aes128Eme2 = Eme2<aes::Aes128>;

let key = [0x42; 48];
let tweak = [0x24; 16];
let plaintext = b"hello world! this is my plaintext! it needs to be longer.";
let mut buf = plaintext.to_vec();

// Initialize using standard KeyIvInit (hashes the tweak via `Eme2::hash_ad`)
let cipher = Aes128Eme2::new(&key.into(), &tweak.into());

// Encrypt in-place
cipher.encrypt(&mut buf).expect("encryption succeeded");
assert_ne!(buf[..], plaintext[..]);

// Decrypt in-place
cipher.decrypt(&mut buf).expect("decryption succeeded");
assert_eq!(buf[..], plaintext[..]);

Encryption with associated data

use eme2_extended::Eme2;
use eme2_extended::cipher::KeyInit;

type Aes128Eme2 = Eme2<aes::Aes128>;

let key = [0x42; 48];
let associated_data = b"associated data";
let plaintext = b"hello world! this is my plaintext! it needs to be longer.";
let mut buf = plaintext.to_vec();

// Initialize cipher using the base KeyInit trait
let cipher = <Aes128Eme2 as KeyInit>::new(&key.into());

// Encrypt in-place, hashing the associated data into the tweak internally
cipher.encrypt_with_ad(associated_data, &mut buf).expect("encryption succeeded");
assert_ne!(buf[..], plaintext[..]);

// Decrypt in-place
cipher.decrypt_with_ad(associated_data, &mut buf).expect("decryption succeeded");
assert_eq!(buf[..], plaintext[..]);

Re-exports

pub use cipher;

Structs

Eme2

EME2 cipher mode.

Enums

Error

Error types for EME2 operations.

Traits

EmePoly

A trait for block sizes that support EME2 Galois Field polynomial arithmetic.