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ARIA-CFB

Algorithm​

Cipher feedback (CFB) with ARIA uses a 16-byte shift register. Each step encrypts the register with ARIA in the forward direction to produce up to 16 bytes of keystream, XORed with the next input segment. The register is then shifted and extended with ciphertext bytes: on encryption the feedback is the ciphertext segment just produced; on decryption the feedback is the ciphertext segment read from input (decryption still only runs the block cipher in the encrypt direction on the register).

This implementation is ARIA-CFB-128 (128-bit block / segment size). Output length equals input length. There is no authentication tag.

Purpose​

Use ARIA-CFB with a shared AriaCipher when a profile requires ARIA in CFB. For new designs that need integrity, prefer an AEAD such as AES-GCM or ChaCha20-Poly1305 unless the standard mandates ARIA-CFB plus a separate MAC.

Rust API​

  • Crate: noxtls-crypto
  • Module path (conceptual): noxtls_crypto::sym (re-exported at crate root)
  • Primary symbols:
    • AriaCipher
    • noxtls_aria_cfb_encrypt
    • noxtls_aria_cfb_decrypt
    • noxtls_aria_cfb_apply

Functions and types:

  • noxtls_aria_cfb_encrypt(cipher, iv, plaintext) -> Vec<u8> - Parameters: cipher is an initialized AriaCipher (128-, 192-, or 256-bit key); iv is a 16-byte initial register; plaintext is arbitrary length. Behavior: ARIA-CFB-128 encryption. Returns: ciphertext Vec<u8> of the same length as plaintext.
  • noxtls_aria_cfb_decrypt(cipher, iv, ciphertext) -> Vec<u8> - Parameters: same cipher and 16-byte iv as used at the start of that stream; ciphertext is the CFB ciphertext. Behavior: inverts CFB-128. Returns: plaintext Vec<u8> of the same length.
  • noxtls_aria_cfb_apply(cipher, iv, input) -> Vec<u8> - Same behavior as noxtls_aria_cfb_encrypt (convenience alias for the forward CFB transform).

Feature flags and policy​

Standard noxtls-crypto build.

Examples​

use noxtls_crypto::{AriaCipher, noxtls_aria_cfb_decrypt, noxtls_aria_cfb_encrypt};

let cipher = AriaCipher::new(&[0x33u8; 16])?;
let iv = [0u8; 16];
let plaintext = b"cfb-message";
let ciphertext = noxtls_aria_cfb_encrypt(&cipher, &iv, plaintext);
let recovered = noxtls_aria_cfb_decrypt(&cipher, &iv, &ciphertext);
assert_eq!(recovered.as_slice(), plaintext.as_slice());
# Ok::<(), noxtls_core::Error>(())

Security and compatibility​

Use an unpredictable unique IV (register seed) per key and message unless your protocol fixes IV derivation. CFB ciphertext is malleable and provides no integrity; pair with a MAC or use AEAD where allowed.