[BIP Draft] Blind Relay: Stateless Encrypted WebSocket Coordination for PSBTs

This proposed BIP, named "Blind Relay," aims to address the current dilemma faced by users in coordinating N-of-M Bitcoin transactions, which currently oscillate between manual, privacy-preserving but cumbersome methods like USB drives or secure messengers, and more convenient yet privacy-compromising stateful coordination servers.

"Blind Relay" introduces an innovative approach utilizing a stateless, ephemeral WebSocket relay that ensures zero-knowledge operation. It encrypts all payloads with AES-GCM-256 encryption client-side, meaning decryption keys are exclusively retained within the client-side URL fragments and never transmitted to the server. This design enables the relay to function entirely in RAM, avoiding any persistent metadata storage or disk storage, with a built-in self-destruct mechanism after a 24-hour time-to-live (TTL) period. This system facilitates real-time coordination for multi-signature transactions without compromising on privacy or creating potential honeypots of information.

The proposal is backed by a reference implementation that has been operational in production for three months, proving its efficacy in facilitating real multisig ceremonies without issues. To support this BIP and encourage further discussion and refinement, links to the draft of the BIP, source code of the implementation, a live client, and related research have been provided. These resources are aimed at soliciting technical feedback from the community on various aspects such as the specification, security model, potential edge cases, and suggestions for improvement. The documents and tools related to this proposal can be accessed through their respective links: the BIP Draft, Source Code, Live Client, and a Related Research Paper.