Function message_request 

pub fn message_request(
    pk_hash: &Digest,
    nonce: &Nonce,
    message: &[u8; 16],
) -> Request

Message: salted digit hash for a 16-byte message.

pk_hash (32 B) ‖ private nonce (16 B) ‖ message (16 B) fills one block exactly. Its 64 output bytes become the 68 digits (digits_kernel in hardware).