your topic title eludes to adding message into a tx

i fully understand you are however embedding the message into the private key before its ECC'd to a public key. much like using the message as a nonce/salt,random addition to private key generation thus YOUR system doesnt even require the extra data on the blockchain(in a tx) as its just seen as a single legacy address

but it requires partners pre-knowledge of private keys+message to create/spend..
which some people dont like the other party knowing the private key