Function seal_detached_precomputed 

pub fn seal_detached_precomputed(
    m: &mut [u8],
    n: &Nonce,
    k: &PrecomputedKey,
) -> Tag

seal_detached_precomputed() encrypts and authenticates a message m using a precomputed key k and a nonce n. m is encrypted in place, so after this function returns it will contain the ciphertext. The detached authentication tag is returned by value.