Kiminuo, this was discussed here: https://github.com/bitcoin/bips/pull/49
On Fri, Sep 8, 2023 at 2:39 PM kiminuo via bitcoin-dev < bitcoin-dev@lists.linuxfoundation.org> wrote: > [Formatted version of this post is here: > https://gist.github.com/kiminuo/cc2f19a4c5319e439fc7be8cbe5a39f9] > > Hi all, > > BIP 21 [https://github.com/bitcoin/bips/blob/master/bip-0021.mediawiki] > defines a URI scheme for making Bitcoin payments and the purpose of the URI > scheme is to enable users to easily make payments by simply clicking links > on webpages or scanning QR Codes. An example of a BIP21 URI is: > > > bitcoin:bc1qd4fxq8y8c7qh76gfnvl7amuhag3z27uw0w9f8p?amount=0.004&label=Kiminuo&message=Donation > > Now to make it easier, these URIs are typically clickable. Bitcoin wallets > register the "bitcoin" URI scheme so that a BIP21 URI is parsed and data > are pre-filled in a form to send your bitcoin to a recipient. Notably, > wallets do not send your bitcoin once you click a BIP21 URI, there is still > a confirmation step that requires user's attention. Very similar experience > is with a QR code that encodes a BIP21 URI where one just scans a QR code > and data is, again, pre-filled in a wallet's UI for your convenience. > > While working on Wasabi's BIP21 implementation I noticed that based on the > BIP21 grammar [ > https://github.com/bitcoin/bips/blob/master/bip-0021.mediawiki#abnf-grammar], > it is actually allowed to specify URI parameters multiple times. This means > that the following URI is actually valid: > > bitcoin:bc1qd4fxq8y8c7qh76gfnvl7amuhag3z27uw0w9f8p?amount=0.004&label=Kiminuo&message=Donation&amount=1.004 > (note that the 'amount' parameter is specified twice) > > Bitcoin Core implements "the last value wins" behavior[^3] so amount=1.004 > will be taken into account and not "amount=0.004"[^4]. However, in general, > the fact that the same parameter can be specified multiple times can lead > to a confusion for users and developers[^1][^2]. In the worst case, it > might be exploited by some social engineering attempts by attempting to > craft a 'clever' BIP21 URI and exploting behavior of a particular wallet > software. For the record, I'm not aware that it actually happens, so this > is rather a concern. > > The main question of this post is: Is it useful to allow specifying BIP21 > parameters multiple times or is it rather harmful? > > Regards, > K. > > [^1]: https://github.com/JoinMarket-Org/joinmarket-clientserver/pull/1510 > [^2]: > https://github.com/MetacoSA/NBitcoin/blob/93ef4532b9f2ea52b2c910266eeb6684f3bd25de/NBitcoin/Payment/BitcoinUrlBuilder.cs#L74-L78 > [^3]: I added a test to that effect in > https://github.com/bitcoin/bitcoin/pull/27928/files, see > https://github.com/bitcoin/bitcoin/blob/83719146047947e588aa0c7b5eee02f44884553d/src/qt/test/uritests.cpp#L68-L73 > . > [^4]: You can test your wallet's behavior by scanning the last image here > https://github.com/zkSNACKs/WalletWasabi/pull/10578#issue-1687564404 (or > directly > https://user-images.githubusercontent.com/58662979/265389405-16893ce8-7c19-4262-bb60-5fd711336685.png > ). > _______________________________________________ > bitcoin-dev mailing list > bitcoin-dev@lists.linuxfoundation.org > https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev >
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