Date: Wed, 12 Oct 2022 09:04:35 +0000
To: woltx <woltx@protonmail.com>
From: alicexbt <alicexbt@protonmail.com>
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Cc: "bitcoin-dev@lists.linuxfoundation.org"
 <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Silent Payment v4 (coinjoin support added)
Precedence: list

Hi=C2=A0woltx,

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 wo=
uld 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 com=
pressed public key with even y.=20

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

> Tutorial updated: https://gist.github.com/w0xlt/c81277ae8677b6c0d3dd07389=
3210875
> "warnings": "This address is not a new identity. It is a re-use of an exi=
sting 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:
>=20
> . Silent payments now use all inputs to create transactions. Previously, =
they only used the first input. This change increases privacy and makes sil=
ent payments compatible with coinjoin.
>=20
> . `getspaddress` RPC renamed to `getsilentaddress` for clarity
>=20
> . Added support for silent payment in PSBT via `walletcreatefundedpsbt` R=
PC.
>=20
> . Added a new index scheme (which stores the sum of input public keys for=
 each transaction). The previous index `bitcoin/signet/indexes/silentpaymen=
tindex` should be removed as it is no longer compatible with this new versi=
on.
>=20
> For reviewers:
>=20
> Now, silent payments use the scheme `hash(i1*X + i2*X + i3*X + ...)*G + X=
 =3D=3D hash(x*(I1+I2+I3+...))*G + X`, as described here: https://gist.gith=
ub.com/RubenSomsen/c43b79517e7cb701ebf77eec6dbb46b8#variant-using-all-input=
s
>=20
> As inputs can be Taproot, this introduced a new issue as `bitcoin-core/se=
cp256k1` does not support x-only public key sum (perhaps due to missing pre=
fix byte).
>=20
> I opened a new PR (#1143) to add a function to convert from x-only to com=
pressed public key with even y. This is the solution being used by the curr=
ent silent payment implementation.
>=20
> Tutorial updated: https://gist.github.com/w0xlt/c81277ae8677b6c0d3dd07389=
3210875