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Bitcoin–Monero Cross-chain Atomic Swap
44 Commits 73 Branches 28 Tags 81 MiB
Rust 99.8%
Shell 0.2%
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rishflab 39afb4196b Save and recover protocol state from disk 
NOTE: This implementation saves secrets to disk! It is not
secure.

The storage API allows the caller to atomically record the state
of the protocol. The user can retrieve this recorded state and
re-commence the protocol from that point. The state is recorded
using a hard coded key, causing it to overwrite the previously
recorded state. This limitation means that this recovery
mechanism should not be used in a program that simultaneously
manages the execution of multiple swaps.

An e2e test was added to show how to save, recover and resume
protocol execution. This logic could also be integrated into the
run_until functions to automate saving but was not included at
this stage as protocol execution is currently under development.

Serialisation and deserialisation was implemented on the states
to allow the to be stored using the database. Currently the
secret's are also being stored to disk but should be recovered
from a seed or wallets.
2020-10-21 18:39:45 +11:00
.github/workflows Increase Rust minimum stack size in CI 2020-10-21 16:09:24 +11:00
monero-harness Remove redundant license 2020-09-28 17:18:02 +10:00
xmr-btc Save and recover protocol state from disk 2020-10-21 18:39:45 +11:00
.gitignore Use intellij rust gitignore 2020-10-09 11:40:00 +11:00
bors.toml Swap Monero for Bitcoin 2020-09-28 17:15:57 +10:00
BTC_XMR_atomic_swap_protocol.svg Fix embedded image 2020-10-09 09:45:48 +11:00
Cargo.toml Swap Monero for Bitcoin 2020-09-28 17:15:57 +10:00
LICENSE Change license to GPLv3 2020-10-12 17:13:25 +11:00
README.md Fix typo 2020-10-09 09:49:39 +11:00
rust-toolchain Swap Monero for Bitcoin 2020-09-28 17:15:57 +10:00
rustfmt.toml Swap Monero for Bitcoin 2020-09-28 17:15:57 +10:00

README.md

XMR to BTC Atomic Swap

This repository is a proof of concept for atomically swapping XMR for BTC.

We define:

  • Alice to be the actor that initially holds XMR.
  • Bob to be the actor that initially holds BTC.

In the best-case scenario the protocol looks like this:

  1. Alice and Bob exchange a set of addresses, keys, zero-knowledge proofs and signatures.
  2. Bob publishes Tx_lock, locking up his bitcoin in a 2-of-2 multisig output owned by Alice and Bob. Given the information exchanged in step 1, Bob can refund his bitcoin if he waits until time t_1 by using Tx_cancel and Tx_refund. If Bob doesn't refund after time t_1, Alice can punish Bob for being inactive by first publishing Tx_cancel and, after t_2, spending the output using Tx_punish.
  3. Alice sees that Bob has locked up the bitcoin, so she publishes Tx_lock on the Monero blockchain, locking up her monero in an output which can only be spent with a secret key owned by Alice (s_a) and a secret key owned by Bob (s_b). This means that neither of them can actually spend this output unless they learn the secret key of the other party.
  4. Bob sees that Alice has locked up the monero, so he now sends Alice a missing key bit of information which will allow Alice to redeem the bitcoin using Tx_redeem.
  5. Alice uses this information to spend the bitcoin to an address owned by her. When doing so she leaks her Monero secret key s_a to Bob through the magic of adaptor signatures.
  6. Bob sees Alice's Tx_redeem on Bitcoin, extracts Alice's secret key from it and combines it with his own to spend the monero to an address of his own.

BTC/XMR atomic swap protocol

The repository is structured as a library and a single test function that executes the swap. The library has the following modules:

  • alice: Defines the state machine that describes the swap for Alice. This includes the messages sent to/from Alice.
  • bob: Defines the state machine that describes the swap for Bob. This includes the messages sent to/from Bob.
  • bitcoin: Keys, signing functions, transactions etc. for Bitcoin. Also includes a test wallet (see below).
  • monero: Keys, signing functions, transactions etc. for Monero. Also includes a test wallet (see below).

Currently we have a single test function that proves the following:

  • Interaction with both block chains and their respective wallets works.
  • The messages required are correct and can manually drive the state transitions to execute a swap.
  • It is possible to interact with, and watch, the monero blockchain using monero-wallet-rpc.
  • It is possible to watch a bitcoind instance using bitcoin-harness (we already knew this :)

Currently we do not do:

  • Actual network communication.
  • Verification that the UI is acceptable. Since we do everything in a single test function there is no user interaction, this is unrealistic for a real product.

Testing

We wrote a few additional libraries to facilitate testing:

Wallets

  • bitcoin module contains a test wallet by way of bitcoind.
  • monero: module contains a test wallet by way of monero-wallet-rpc.

Blockchain harnesses

We have written two harnesses for interacting with bitcoin and monero.

These harnesses wrap interaction with bitcoind and monerod/monero-wallet-rpc.

We use testcontainers-rs to spin up bitcoind, monerod, and monero-wallet-rpc in docker containers during unit/integration testing.