One can easily insert a public note into a transaction, but it is not encrypted. It would be useful to encrypt small amounts of data in this field, such that only the recipient of the transaction can decrypt it, using their own private key.
Any current wallets support this? (I am aware of bitmessage, but that is a different blockchain. I am only talking about the btc blockchain, not alts).
You could use the OP_RETURN bytes to do this but as there are only 80 such bytes I think that would make it pretty difficult to add anything other than a very small encrypted message.
The point of Bitcoin is not encrypted messaging or the like - it is just an open, distributed ledger with no central control.
