Function encrypt_bytes 

pub fn encrypt_bytes(
    plaintext: &[u8],
    key: &[u8; 32],
    nonce: &[u8; 24],
    aad: &[u8],
) -> Result<(Vec<u8>, Algorithm), CryptError>

Encrypts the given plaintext, authenticating aad alongside it.

In v2 the associated data is always a serialized HeaderBinding, which ties the ciphertext to its header and its purpose (filename vs content).