Date: Sat, 12 Aug 2023 21:20:37 +0000
To: Christopher Allen <ChristopherA@lifewithalacrity.com>
From: Dan Gould <d@ngould.dev>
Message-ID: <ACC80254-1AE2-4B6E-8D5C-A3C3FACCA6EA@ngould.dev>
In-Reply-To: <CACrqygAPKUUYxWbV0XwrRN9U1sNEGCkv+iWwA8MiLLjN_+dASQ@mail.gmail.com>
References: <mailman.130337.1691684480.956.bitcoin-dev@lists.linuxfoundation.org>
 <50A19B79-46A1-4F21-AA53-74356F4B0CBA@ngould.dev>
 <P1bXSK5FgAsqtckOyZmQ4U6XyKJavBuDC92FgE_R4osiQJIIEDndFRPBFJsU6vO0fhioctnDV9MKp1sYoCfSwswUbFfkglxHEvYaNMo67fI=@proton.me>
 <CACrqygAPKUUYxWbV0XwrRN9U1sNEGCkv+iWwA8MiLLjN_+dASQ@mail.gmail.com>
Feedback-ID: 13175031:user:proton
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable
Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] BIP for Serverless Payjoin
Precedence: list

Blockchain Commons UR seems to be the most elegant choice since QRs are com=
monplace. This suggestion, along with Adam=E2=80=99s to reconsider DH over =
symmetric crypto would let us encode a pub key directly in the `pj=3D` endp=
oint rather than with a separate  am somewhat concerned that some payjoin i=
mplementations are written in JavaScript and would benefit most from a v2 u=
pgrade in order to support receiving, but no JavaScript ur library exists y=
et. Perhaps one could be bound from the rust implementation.

I have updated the draft to include these suggestions and posted it to the =
bips repo: https://github.com/bitcoin/bips/pull/1483

The biggest change is that symmetric crypto is replaced with a Noise IK-bas=
ed cryptosystem using Secp256k1/Sha256/ChaChaPoly1305 to address the proble=
ms waxwing helped uncover.

I hope also to hear more input on the transport protocol. I know many devel=
opers are interested in Nostr for its censorship resistant properties and w=
ould like to see that discussion play out within the BIP process to reach r=
ough consensus before deployment. This hope is a key reason I=E2=80=99ve wr=
itten here first instead of developing and deploying a complete reference i=
mplementation.

Thanks list,

Dan

> On Aug 11, 2023, at 9:05 PM, Christopher Allen <ChristopherA@lifewithalac=
rity.com> wrote:
>=20
>=20
>=20
> On Fri, Aug 11, 2023 at 3:29 PM symphonicbtc via bitcoin-dev <bitcoin-dev=
@lists.linuxfoundation.org> wrote:
> Quick little nit I noticed as well, are you sure base64 encoding is the b=
est choice for the psk in the URI? You may find that having to urlencode th=
e special characters in base64 it impacts readability and adds a layer of c=
omplexity if a human wanted to extract the psk from the URI for some reason=
. I suggest using something like [base64url](https://datatracker.ietf.org/d=
oc/html/rfc4648#section-5) which modifies base64 slightly to be more suited=
 to this purpose.
>=20
> Yes, the URI version of base64 is better.
> However, If you plan to display these via QRs, either will double the den=
sity of the QR as QR libraries treat them as binary data (like hex of hex d=
ata). Thus you may want to use UR encoding, which is what over a dozen bitc=
oin wallets use to encode PSBTs. URs are very efficient with QRs, and have =
the optional benefit that if the data carried becomes too large, they can b=
e animated. The have other advantages.=20
>=20
> * A top level link about URs:=20
> https://github.com/BlockchainCommons/crypto-commons/blob/master/Docs/READ=
ME.md#uniform-resources-urs
>=20
> * About the base64 encoding with QRs problem:=20
> https://github.com/BlockchainCommons/Research/blob/master/papers/bcr-2020=
-003-uri-binary-compatibility.md
>=20
> * The base UR tech spec:=20
> https://github.com/BlockchainCommons/Research/blob/master/papers/bcr-2020=
-005-ur.md
>=20
> * List of bitcoin wallets using UR for PSBTs:=20
> https://github.com/blockchaincommons/gordian-developer-community#urs
>=20
> * List of UR libraries:=20
> https://github.com/BlockchainCommons/crypto-commons#bc-ur
>=20
> Let me know if you=E2=80=99re interested.
>=20
> =E2=80=94 Christopher Allen