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ARIA-CBC

Algorithm​

ARIA is a 128-bit block cipher (KR standard, roughly comparable role to AES in Korean profiles). CBC XORs each plaintext block with the previous ciphertext block before encryption (the first block uses the IV). Decryption inverts that chain using the same IV.

These helpers use a 16-byte IV and require block-aligned buffers: plaintext and ciphertext lengths must be multiples of 16. They do not apply or strip PKCS padding; callers must pad or choose another mode if payloads are not already a whole number of blocks.

Purpose​

Use ARIA-CBC with a shared AriaCipher key schedule when a protocol or deployment specifies ARIA in CBC (for example national or industry profiles). For new designs that need integrity, prefer an AEAD (for example AES-GCM or ChaCha20-Poly1305) unless the profile mandates ARIA-CBC 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_cbc_encrypt
    • noxtls_aria_cbc_decrypt

Functions and types:

  • noxtls_aria_cbc_encrypt(cipher, iv, plaintext) -> Result<Vec<u8>> - Parameters: cipher is an initialized AriaCipher (128-, 192-, or 256-bit key via AriaCipher::new); iv is a 16-byte initialization vector; plaintext must be block-aligned (length multiple of 16). Behavior: encrypts in ARIA-CBC. Returns: ciphertext Vec<u8> of the same length on success, or InvalidLength if the buffer is not a multiple of 16 bytes.
  • noxtls_aria_cbc_decrypt(cipher, iv, ciphertext) -> Result<Vec<u8>> - Parameters: same cipher and 16-byte iv as used for that CBC stream; ciphertext must also be block-aligned. Behavior: decrypts ARIA-CBC. Returns: plaintext Vec<u8> of the same length on success, or InvalidLength if misaligned.

Feature flags and policy​

Standard noxtls-crypto build (ARIA-CBC is always available; ARIA-ECB is behind hazardous-legacy-crypto).

Examples​

use noxtls_crypto::{AriaCipher, noxtls_aria_cbc_decrypt, noxtls_aria_cbc_encrypt};

let cipher = AriaCipher::new(&[0x22u8; 16])?;
let iv = [0u8; 16];
let plaintext = [0x44u8; 16];
let ciphertext = noxtls_aria_cbc_encrypt(&cipher, &iv, &plaintext)?;
let recovered = noxtls_aria_cbc_decrypt(&cipher, &iv, &ciphertext)?;
assert_eq!(recovered, plaintext);
# Ok::<(), noxtls_core::Error>(())

Security and compatibility​

Use an unpredictable unique IV per key and message when your threat model requires semantic security (TLS and similar standards define how IVs are formed). CBC does not authenticate ciphertext; bit flips propagate predictably at the block level. Combine with a MAC or use AEAD where the protocol allows.