Good morning Adam, > And I'm reminded that a related point is made by belcher in the gist > comment thread iirc (after we discussed it on IRC): over time a > "PayJoin-only" merchant doing the simplest thing - using a single utxo > over and over again, will concentrate more and more funds into it, and > inevitably violating UIH2 in an increasingly dramatic fashion > (contributing a 100BTC utxo to a 0.1BTC payment etc.). Suggesting it's > better if there's a mix of payjoin/non-payjoin.
To be pedantic: as I understand bustapay, it would still not violate UIH2 (unless I misunderstand UIH2). Suppose the original transaction is: (0.05 payer, 0.07 payer) -> (0.1 payee, 0.02 payer) Then bustapay with such a PayJoin-only merchant with 100BTC UTXO would give: (100 payee, 0.05 payer, 0.07 payer) -> (100.1 payee, 0.02 payer). As I understand it, this technically does not violate UIH2. It would still conceivably be interpreted as a payment of 100.1 BTC, from a payer who happens to have massively lopsided UTXOs being owned, but still does not violate UIH2. However, if that 100.1 UTXO is subsequently used to pay a 100.3 payment, then that is used to pay a 100.7 payment, that strongly suggests such a naive PayJoin-only merchant. Perhaps a simple heuristic against this would be: 1. For every UTXO you own, flip a coin. If all of them come up heads, do not payjoin; just broadcast the original transaction. 2. Else, randomly select a UTXO (value not care?) and payjoin with that UTXO. However, I have no proper analysis of the blockchain, so -- Regards, ZmnSCPxj _______________________________________________ bitcoin-dev mailing list email@example.com https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev