Function message_encrypt 

pub async fn message_encrypt<R>(
    ptext: &[u8],
    remote_address: &ProtocolAddress,
    session_store: &mut dyn SessionStore,
    identity_store: &mut dyn IdentityKeyStore,
    now: SystemTime,
    csprng: &mut R,
) -> Result<CiphertextMessage, SignalProtocolError>
where
    R: Rng + CryptoRng,