Subject: Re: [bitcoin-dev] [BIP proposal] Private Payments

From: Alfred Hodler <[email-masked]>
Date: Mon, 11 Jul 2022 10:28:40 +0000

Update: Bob doesn't have to watch all address types he's advertising. When notifying Bob, Alice will pick one address type out of the ones Bob is advertising and include it in the notification. That way even if Bob's wallet accepts many address types, he still doesn't have to watch all of them for each Alice.

The previous spec reads:

> Alice then constructs a 72-byte OP_RETURN output whose value is set to `BIPXXXX + notification + N_Alice` (`+` is concat) and sends it in a transaction containing no other outputs (XXXX to be replaced once a BIP number is assigned).

We can extended the payload to 73 bytes and define it as: `BIPXXXX + notification + N_Alice + address_type`, where `address_type` is a single byte containing the desired address type index (1 out of 16, limited by Bob's payment code). If Alice ever wants to start sending to a different address type, she can simply re-notify Bob and Bob will switch to a new address type in the case of Alice.

Alfred