Published on: 2022-06-11T14:30:13+00:00
At Pizza Day Prague 2022, a discussion was held regarding the improvement of BIP47, which focused on minimizing the on-chain space required and outsourcing the notification transaction to break the sender/recipient link. The current implementation of BIP47 requires an input key for blinding, the blinded sender payment code in an op_return, and the recipient key in an output. However, it was suggested that the requirement for the recipient to learn the payment code of the sender could be foregone, as it is not necessary and could potentially save space. The minimum notification payload required is a fresh sender key and a static recipient key.Another idea discussed was to put multiple notifications in a single transaction, which can then be outsourced to a third party. This third party could be paid over the Lightning Network for their services in breaking the sender/recipient link. One possible solution proposed was to use the taproot annex to insert the notification payload as discounted witness data. However, this approach would require custom software for the recipient to notice the notification, as it is not tied to an easily noticeable output. Alternatively, the sender keys could be included in the transaction while still creating an output for each recipient key.During the discussion, an interesting point was raised regarding the representation of the recipient key. It was suggested that it could be represented using only 4 bytes, leaving a window of 1 in ~4.3 billion for a collision. This would significantly reduce the payload from 64 bytes to 36 bytes of witness data. However, it should be noted that using the annex makes the transaction non-standard. Therefore, it was proposed that either the annex should be standardized as the first use case or an alternative method should be considered.The participants in the discussion included Alekos Filini, Martin Habovštiak, Daniela Brozzoni, Eric Sirion, Pavol Rusnak, Salvatore Ingala, and others. Relevant materials such as Silent Payments and BIP47 were provided for reference.Overall, the discussion revolved around minimizing the on-chain space required for BIP47 and outsourcing the notification transaction to a third party in order to break the sender/recipient link. Additionally, the idea of representing the recipient key with only 4 bytes was discussed, which would significantly reduce the payload size.
Updated on: 2023-08-02T06:47:26.626141+00:00