Multiple notifications in a single transaction #16
Description
Upon the lifting of limits in Bitcoin Core's relay policy regarding op_return, to be released on October 2025, I think BIP47 v1/v2 could be upgraded to allow multiple notifications in a single transaction.
This would obviously make it cheaper to start the "channel" and maybe improve privacy, since there'll be a single change output for many "channels".
One possible way it could work:
For the sender, in step 5 of the notification transaction:
Alice adds an OP_RETURN output to her transaction which consists of P.
Alice would be able to add, in a single op_return output, PBob, PCharlie, PDina etc separated by the push opcodes.
If a receiving wallet identifies a payment to its notification address, it would:
- if there's a single notification data, operate as usual;
- if there are multiple, the first data would be applicable to the first notification address output, 2nd data to 2nd output etc (the change output, if existent, would be the last);
Alternatively, multiple op_return outputs could be used in the notification transaction, although that would cost more, since each needs its own amount field.
The bytes reserved for future expansion could be used to signal that payment code supports this new notification. If I remember correctly, this was how Samourai Wallet's Paynym directory signalled that the user supported segwit.