Re: [bitcoin-dev] Silent Payment v4 (coinjoin support added)

[alicexbt <alicexbt@protonmail.com>]

Hi woltx,

Thanks for working on silent payments improving it in each version.

1) All inputs being used sounds good although I do not understand how it would benefit coinjoin.
2) New RPC command name is better.

> I opened a new PR (#1143) to add a function to convert from x-only to compressed public key with even y. 

Not sure about the concerns expressed by Andrew Poelstra in the pull request related to rogue-key attacks.

> Tutorial updated: https://gist.github.com/w0xlt/c81277ae8677b6c0d3dd073893210875
> "warnings": "This address is not a new identity. It is a re-use of an existing identity with a different label."

I could not understand the warning in the output for `getsilentaddress` RPC when used with a label.

/dev/fd0

Sent with Proton Mail secure email.

------- Original Message -------
On Tuesday, October 11th, 2022 at 12:32 PM, woltx via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:


> Silent Payment v4 (coinjoin support added)
> Changes:
> 
> . Silent payments now use all inputs to create transactions. Previously, they only used the first input. This change increases privacy and makes silent payments compatible with coinjoin.
> 
> . `getspaddress` RPC renamed to `getsilentaddress` for clarity
> 
> . Added support for silent payment in PSBT via `walletcreatefundedpsbt` RPC.
> 
> . Added a new index scheme (which stores the sum of input public keys for each transaction). The previous index `bitcoin/signet/indexes/silentpaymentindex` should be removed as it is no longer compatible with this new version.
> 
> For reviewers:
> 
> Now, silent payments use the scheme `hash(i1*X + i2*X + i3*X + ...)*G + X == hash(x*(I1+I2+I3+...))*G + X`, as described here: https://gist.github.com/RubenSomsen/c43b79517e7cb701ebf77eec6dbb46b8#variant-using-all-inputs
> 
> As inputs can be Taproot, this introduced a new issue as `bitcoin-core/secp256k1` does not support x-only public key sum (perhaps due to missing prefix byte).
> 
> I opened a new PR (#1143) to add a function to convert from x-only to compressed public key with even y. This is the solution being used by the current silent payment implementation.
> 
> Tutorial updated: https://gist.github.com/w0xlt/c81277ae8677b6c0d3dd073893210875