Hello, 
The transport layer problem is well addressed here. The complementary piece 
— ensuring signers can independently validate transaction invariants before 
signing, regardless of how the PSBT was relayed — is what I've been 
exploring with BTSL: 
https://delvingbitcoin.org/t/btsl-bitcoin-transaction-schema-language-a-declarative-validation-schema-for-psbt-workflows/2338

Best regards, 
Thomas Suau

Le mercredi 25 mars 2026 à 13:21:39 UTC+1, Sean Carlin a écrit :

> Hi everyone,
>
> I'd like to propose a new BIP for real-time, trust-minimized coordination 
> of multi-signature PSBTs.
>
> The Problem
> Coordinating N-of-M Bitcoin transactions currently forces users into a 
> binary choice:
> - Manual out-of-band transfers (USB drives, secure messengers) that 
> preserve privacy but introduce high friction and error risk, or
> - Stateful coordination servers that offer good UX but act as privacy 
> honeypots, logging metadata, signer relationships, and often storing PSBTs 
> on disk.
>
> The Proposal: Blind Relay
> This BIP introduces a "Blind Relay" - an ephemeral, stateless, 
> zero-knowledge WebSocket relay. All payloads are encrypted client-side with 
> AES-GCM-256, with decryption keys held exclusively in client-side URL 
> fragments (never sent to the server). The relay operates entirely in RAM 
> with a strict 24-hour TTL and self-destructs upon completion, providing 
> real-time coordination without persistent metadata or disk storage.
>
> A reference implementation has been running in production for three 
> months, successfully facilitating real multisig ceremonies.
>
> *Links*
> - BIP Draft: 
> https://github.com/scarlin90/bip-stateless-psbt-coordination/blob/main/bip-draft.md
> - Source Code: https://github.com/scarlin90/signingroom
> - Live Client: https://signingroom.io
> - Related Research Paper: https://arxiv.org/abs/2601.17875
>
> I look forward to your technical feedback - especially on the 
> specification, security model, edge cases, and any suggested improvements.
>
> Best regards,
> Sean Carlin

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