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chris-belcher / work-diary
Last active Dec 5, 2020
Chris Belcher work diary
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I keep a diary of all the work I do on bitcoin privacy.
It may also be interesting to my collaborators and donors, and anyone who wants to follow
how my projects are going (these days I'm almost exclusively working on developing
CoinSwap, see https://gist.github.com/chris-belcher/9144bd57a91c194e332fb5ca371d0964).
(Note: I use the datetime format YYYY-MM-DD)
= week-2020-11-30 =
working on initial sync of core wallet including coinswap addresses, not just the xpubs
@chris-belcher
chris-belcher / coinswap-design.md
Last active Dec 2, 2020
Design for a CoinSwap Implementation for Massively Improving Bitcoin Privacy and Fungibility
View coinswap-design.md

Design for a CoinSwap Implementation for Massively Improving Bitcoin Privacy and Fungibility

25/5/2020

Abstract

Imagine a future where a user Alice has bitcoins and wants to send them with maximal privacy, so she creates a special kind of transaction. For anyone looking at the blockchain her transaction appears completely normal with her coins seemingly going from address A to address B. But in reality her coins end up in address Z which is entirely unconnected to either A or B.

Now imagine another user, Carol, who isn't too bothered by privacy and sends her bitcoin using a regular wallet which exists today. But because Carol's transaction looks exactly the same as Alice's, anybody analyzing the blockchain must now deal with the possibility that Carol's transaction actually sent her coins to a totally unconnected address. So Carol's privacy is improved even though she didn't change her behaviour, and perhaps had never even heard of this software.

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chris-belcher / pro-decentralization-link-list.md
Last active Nov 25, 2020
pro-decentralization-link-list
View pro-decentralization-link-list.md
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chris-belcher / JMalert.md
Last active Nov 18, 2020
JoinMarket release 0.2.0 ameliorates this snooping attack.
View JMalert.md
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chris-belcher / sorted-merkle-tree-issue693.md
Last active Oct 13, 2020
Sorted merkle tree as solution to issue #693
View sorted-merkle-tree-issue693.md

The Problem

JoinMarket has a problem where it assumes different nicknames have different bitcoin wallets. This can be exploited by people running multiple yield generator bots from the same wallet, so they get a higher rate of profit at the expense of de-legitimizing the system for privacy.

Crypto primitive 1: Merkle Tree

A merkle tree is a way of producing a commitment to a set, which can later can prove that elements are contained within the set using only O(logN) data, and only revealing one other element in the set.

For example here is a merkle tree commiting to a set of numbers {6, 3, 9, 0, 8, 4, 7, 2}

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chris-belcher / design-for-improving-joinmarkets-resistance-to-sybil-attacks-using-fidelity-bonds.md
Last active May 29, 2020
Design for improving JoinMarket's resistance to sybil attacks using fidelity bonds
View design-for-improving-joinmarkets-resistance-to-sybil-attacks-using-fidelity-bonds.md

Design for improving JoinMarket's resistance to sybil attacks using fidelity bonds

13/7/2019

tl;dr

JoinMarket can be sybil attacked today at relatively low cost which can destroy its privacy. Bitcoins can be sacrificed with burner outputs and time-locked addresses (also called fidelity bonds), and this can be used to greatly improve JoinMarket's resistance to sybil attacks.

With real-world data and realistic assumptions we calculate that under such a fidelity bond system an adversary would need to lock up 30,000-80,000 bitcoins for months, or send 45-120 bitcoins to burner addresses to have a good chance of sybil attacking the system if it were added to JoinMarket.

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chris-belcher / financial-mathematics-of-joinmarket-fidelity-bonds.md
Last active May 27, 2020
Financial mathematics of joinmarket fidelity bonds
View financial-mathematics-of-joinmarket-fidelity-bonds.md

Financial mathematics of JoinMarket fidelity bonds

13/7/2019

To read the context see the main document Design for improving joinmarket's resistance to sybil attacks using fidelity bonds.

Valuing fidelity bonds

We want to come up with a mathematical formula which gives the value of a fidelity bond. We want this function to be in the best interests of takers who use it. We aim for them to get the best possible sybil resistance.

@chris-belcher
chris-belcher / privacy-liquidity-divisibility.md
Last active May 26, 2020
How Wasabi Wallet and Samourai Wallet slightly degrade the divisibility of bitcoin
View privacy-liquidity-divisibility.md

How Wasabi Wallet and Samourai-Wallet-Whirlpool slightly degrade the divisibility of bitcoin

December 2018

I made this claim on twitter recently and many people wanted me to go into more detail.

Lots of privacy tech in bitcoin like coinjoin, coinswap, tumblebit and Lightning Network require many entities to come together to agree to make certain kinds of transactions. This creates a requirement that the right resources (coins) have to be in the right place,

@chris-belcher
chris-belcher / joinmarket-with-off-chain-fees.md
Last active May 26, 2020
JoinMarket with off-chain fees
View joinmarket-with-off-chain-fees.md

JoinMarket with off-chain fees

17/01/2019

Problem: Single JoinMarket coinjoins aren't private enough

A single JoinMarket coinjoin often doesn't hide which inputs belong to the maker(s) and which belong to the taker. This is because the coinjoin fee is included on-chain.

To tell apart takers' inputs from makers' inputs, subset matching can be used. The taker's subset is

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