Crypto API: Symmetric ciphers and AEAD

noxtls-crypto::sym includes block/stream transforms and AEAD primitives used by TLS record protection and application payload encryption.

Core cipher type

• AesCipher (initialized with key material once, reused per operation mode).

AES block/stream modes

pub fn noxtls_aes_cbc_encrypt(cipher: &AesCipher, iv: &[u8; 16], plaintext: &[u8]) -> Result<Vec<u8>>
pub fn noxtls_aes_cbc_decrypt(cipher: &AesCipher, iv: &[u8; 16], ciphertext: &[u8]) -> Result<Vec<u8>>
pub fn noxtls_aes_ctr_apply(cipher: &AesCipher, nonce_counter: &[u8; 16], input: &[u8]) -> Vec<u8>

• CBC: requires block-aligned input; returns InvalidLength otherwise.
• CTR: encryption/decryption use the same transform; nonce_counter must be unique per key.

AEAD APIs

pub fn noxtls_aes_gcm_encrypt(
    cipher: &AesCipher,
    nonce: &[u8],
    aad: &[u8],
    plaintext: &[u8],
) -> Result<(Vec<u8>, [u8; 16])>
pub fn noxtls_aes_gcm_decrypt(
    cipher: &AesCipher,
    nonce: &[u8],
    aad: &[u8],
    ciphertext: &[u8],
    tag: &[u8; 16],
) -> Result<Vec<u8>>

• nonce: GCM nonce bytes.
• aad: additional authenticated data (not encrypted, but authenticated).
• tag: 16-byte authentication tag; decryption fails with CryptoFailure on mismatch.

pub fn noxtls_aes_ccm_encrypt(
    cipher: &AesCipher,
    nonce: &[u8],
    aad: &[u8],
    plaintext: &[u8],
) -> Result<(Vec<u8>, [u8; 16])>
pub fn noxtls_aes_ccm_decrypt(
    cipher: &AesCipher,
    nonce: &[u8],
    aad: &[u8],
    ciphertext: &[u8],
    tag: &[u8; 16],
) -> Result<Vec<u8>>

• CCM requires nonce length in 7..=13; enforced by API.

ChaCha20-Poly1305 APIs

pub fn noxtls_chacha20_poly1305_encrypt(
    key: &[u8; 32],
    nonce: &[u8; 12],
    aad: &[u8],
    plaintext: &[u8],
) -> Result<(Vec<u8>, [u8; 16])>
pub fn noxtls_chacha20_poly1305_decrypt(
    key: &[u8; 32],
    nonce: &[u8; 12],
    aad: &[u8],
    ciphertext: &[u8],
    tag: &[u8; 16],
) -> Result<Vec<u8>>

• Verifies tag before decrypt output is accepted.
• Enforces RFC 8439 counter-range bounds for large payloads.

Integration notes

• Never reuse (key, nonce) pairs for AEAD functions.
• Keep AAD format stable and versioned across sender/receiver.
• For TLS record traffic, prefer Connection::seal_record / open_record wrappers instead of direct primitive calls.