Struct MlsCipher 

pub struct MlsCipher { /* private fields */ }

MLS cipher for encrypting and decrypting messages with ChaCha20-Poly1305.

The cipher uses a 32-byte key and derives per-message nonces from a base nonce and message counter. This provides authenticated encryption with additional data (AEAD).

Implementations

impl MlsCipher

pub fn new(key: Vec<u8>, base_nonce: Vec<u8>) -> Self

Creates a new MLS cipher with the given key and base nonce.

Arguments

• key - 32-byte encryption key for ChaCha20-Poly1305
• base_nonce - 12-byte base nonce (XORed with counter for each message)

Security

The key should be securely derived from an MLS key schedule. The base nonce is combined with a counter to ensure unique nonces for each message.

pub fn encrypt( &self, plaintext: &[u8], aad: &[u8], counter: u64, ) -> Result<Vec<u8>>

Encrypts plaintext with authenticated encryption.

Uses ChaCha20-Poly1305 AEAD to encrypt the plaintext and authenticate both the ciphertext and additional authenticated data (AAD).

Arguments

• plaintext - Data to encrypt
• aad - Additional authenticated data (not encrypted, but authenticated)
• counter - Message counter for nonce derivation

Returns

Ciphertext with authentication tag appended (ciphertext.len() == plaintext.len() + 16).

Errors

Returns MlsError::EncryptionError if encryption fails (e.g., invalid key length).

Security

CRITICAL: Never reuse the same counter with the same key. Counter reuse completely breaks ChaCha20-Poly1305 security.

pub fn decrypt( &self, ciphertext: &[u8], aad: &[u8], counter: u64, ) -> Result<Vec<u8>>

Decrypts ciphertext with authenticated decryption.

Uses ChaCha20-Poly1305 AEAD to decrypt and verify the authentication tag. Both the ciphertext and AAD are authenticated.

Arguments

• ciphertext - Encrypted data with authentication tag appended
• aad - Additional authenticated data (must match encryption AAD)
• counter - Message counter for nonce derivation (must match encryption counter)

Returns

Decrypted plaintext.

Errors

• MlsError::DecryptionError - Authentication tag verification failed or decryption failed
• MlsError::EncryptionError - Invalid key length

Security

Authentication failure indicates either:

• Wrong key
• Tampered ciphertext
• Wrong AAD
• Wrong counter

pub fn key(&self) -> &[u8]

Gets the encryption key.

pub fn base_nonce(&self) -> &[u8]

Gets the base nonce.

Trait Implementations

impl Clone for MlsCipher

fn clone(&self) -> MlsCipher

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for MlsCipher

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.