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

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

[woltx]

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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

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

[alicexbt]

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

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

[woltx]

Hi /dev/fd0

I haven't accessed ML for a while.

1) All inputs being used sounds good although I do not understand how it would benefit coinjoin.

Using all inputs, it becomes possible to use SP addresses in coinjoins as long as all participants agree.
More information:
https://gist.github.com/RubenSomsen/c43b79517e7cb701ebf77eec6dbb46b8#variant-using-all-inputs

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

I think Andrew Poelstra is referring to a multi-party scheme.
This is not the case with the Silent Payments scheme, which only relies on transaction data, which is publicly available on the blockchain.

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

This warning was suggested by Aurèle Oulès in https://github.com/bitcoin/bitcoin/pull/24897#issuecomment-1276160738 and the reason was a discussion in PR about users thinking that each address would come from a different key and not the same key.




Sent with Proton Mail secure email.

------- Original Message -------
On Wednesday, October 12th, 2022 at 6:04 AM, alicexbt <alicexbt@protonmail.com> wrote:


> 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

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

[alicexbt]

Hi woltx,

Thanks for the response.

> Using all inputs, it becomes possible to use SP addresses in coinjoins as long as all participants agree.
> More information:
> https://gist.github.com/RubenSomsen/c43b79517e7cb701ebf77eec6dbb46b8#variant-using-all-inputs

Using new addresses and SP address would be same in my opinion in coinjoin.

> I think Andrew Poelstra is referring to a multi-party scheme.
> This is not the case with the Silent Payments scheme, which only relies on transaction data, which is publicly available on the blockchain.

Sounds good.

> This warning was suggested by Aurèle Oulès in https://github.com/bitcoin/bitcoin/pull/24897#issuecomment-1276160738 and the reason was a discussion in PR about users thinking that each address would come from a different key and not the same key.

It makes sense although could be rephrased.

/dev/fd0


Sent with Proton Mail secure email.

------- Original Message -------
On Sunday, October 23rd, 2022 at 12:30 PM, woltx <woltx@protonmail.com> wrote:


> Hi /dev/fd0
> 
> I haven't accessed ML for a while.
> 
> 1) All inputs being used sounds good although I do not understand how it would benefit coinjoin.
> 
> Using all inputs, it becomes possible to use SP addresses in coinjoins as long as all participants agree.
> More information:
> https://gist.github.com/RubenSomsen/c43b79517e7cb701ebf77eec6dbb46b8#variant-using-all-inputs
> 
> 2) Not sure about the concerns expressed by Andrew Poelstra in the pull request related to rogue-key attacks.
> 
> I think Andrew Poelstra is referring to a multi-party scheme.
> This is not the case with the Silent Payments scheme, which only relies on transaction data, which is publicly available on the blockchain.
> 
> 3) I could not understand the warning in the output for `getsilentaddress` RPC when used with a label.
> 
> This warning was suggested by Aurèle Oulès in https://github.com/bitcoin/bitcoin/pull/24897#issuecomment-1276160738 and the reason was a discussion in PR about users thinking that each address would come from a different key and not the same key.
> 
> 
> 
> 
> Sent with Proton Mail secure email.
> 
> 
> ------- Original Message -------
> On Wednesday, October 12th, 2022 at 6:04 AM, alicexbt alicexbt@protonmail.com wrote:
> 
> 
> 
> > 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