RubenSomsen

Silent Payments

Receive private payments from anyone on a single static address without requiring any interaction or extra on-chain overhead.

Update: This now has a BIP and WIP implementation

Overview

The recipient generates a so-called silent payment address and makes it publicly known. The sender then takes a public key from one of their chosen inputs for the payment, and uses it to derive a shared secret that is then used to tweak the silent payment address. The recipient detects the payment by scanning every transaction in the blockchain.

RubenSomsen

L2 protocols

Trust protocols (not always auditable)

• Full custody (Coinbase)
• 2-of-3 arbitration / DLC
• Threshold multisig (ecash, Liquid)
• Off-chain peg-out tx (statechains)
• Collateralized custody

Payment channels

RubenSomsen

Softchains: Sidechains as a Soft Fork via Proof-of-Work Fraud Proofs

Originally posted on bitcoin-dev.

This post describes a fully decentralized two-way peg sidechain design. Activating new sidechains requires a soft fork, hence the name softchains. The key aspect is that all softchains are validated by everyone via Proof-of-Work Fraud Proofs (PoW FP) -- a slow but very efficient consensus mechanism that only requires the validation of disputed blocks. This does increase the validation burden of mainchain full nodes, but only by a minimal amount (~100MB per chain per year). It's similar to [drivechains][0], but without the major downside of having to rely on miners, since all Bitcoin full node users can efficiently validate each sidechain.

Proof-of-Work Fraud Proofs

Last year I posted the idea of [PoW FP to the Bitcoin mailing list][1] ([follow-up here][2]). The idea is that we can use the existence of a fork in Bitc

RubenSomsen

Introduction

I'm Ruben Somsen, Bitcoin Sorcerer. I do protocol design in order to enhance Bitcoin.

I'm sponsored by Spiral, Superlunar/Gemini, HRF, and am currently working on Silent Payments with Josie, assisting Davidson with the implementation of Proof-of-Work fraud proofs into Floresta, and Raj with continuing the work on Teleport (Belcher's Coinswap protocol).

I also help maintain the bitcoin-dev mailing list, co-hosted the Unhashed Podcast, founded the Seoul Bitcoin Meetup in 2014, actively co-organizing BitDevs Amsterdam, and on the layer two funding sub-committee of OpenSats.

You can find me on [Twitter](https://twitter.com/SomsenRube

RubenSomsen

RubenSomsen

Blind Diffie-Hellman Key Exchange (blind ecash)

The goal of this protocol is for Bob to get Alice to perform a Diffie-Hellman key exchange blindly, such that when the unblinded value is returned, Alice recognizes it as her own, but can’t distinguish it from others (i.e. similar to a blind signature).

Alice:
A = a*G
return A

Bob:
Y = hash_to_curve(secret_message)
r = random blinding factor

RubenSomsen

SAS: Succinct Atomic Swap

Works today with [single signer ECDSA adaptor signatures][0], or with Schnorr + MuSig.
Other than the explanation below, there's also a diagram and a video.

 
Advantages:

• Requires merely two on-chain transactions for successful completion, as opposed to four
• Scriptless, and one of the chains doesn't need to support timelocks
• Can be used for efficient privacy swaps, e.g. [Payswap][1]

RubenSomsen

Blind Merged Mining with covenants ( sighash_anyprevout / op_ctv )

Update: the content of this gist is also explained in this Spacechains video.

This write-up was also published on bitcoin-dev.

Blind Merged Mining (BMM) is the idea of committing the hash of another blockchain into a unique location on the Bitcoin blockchain, and paying a Bitcoin fee to miners for the privilege of deciding this hash and capturing the fees inside the other blockchain. Since miners don’t have to know what the hash represents and are simply incentivized to choose the highest bidder, it requires no extra validation on their part (“blind”). This idea was originally conceived of by Paul Sztorc, but required a specific soft fork. [0]

In essence, BMM is a mechanism that allows external blockchains (altcoins, tokens) to outsource their mining to the Bitcoin blockchain. Instead of burning electricity with ASICs, th

RubenSomsen

Spacedollars: Trustless Dollars on a Spacechain

Idea proposed here by Fernando Nieto.

Assuming there is a trustless BTC/USD price oracle, we can burn BTC to create a dollar equivalent amount of "space dollars".

E.g. If the BTC price is $20k, burning 1 BTC gets you 20k space dollars.

The resulting token is the equivalent of the USD: a stable unit of account, but a poor store of value.

RubenSomsen

BIP47 Prague Discussion

This discussion took place at Pizza Day Prague 2022 after a brief discussion on Silent Payments. The main points have been summarized below.

The discussion was mainly between Alekos Filini, Martin Habovštiak, and Ruben Somsen, as well as Daniela Brozzoni, Eric Sirion, Pavol Rusnak, Salvatore Ingala, and others.

This was also posted to the the bitcoin-dev mailing list.

Improving BIP47