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Bitcoin–Monero Cross-chain Atomic Swap
a0ef1f96ec
The bitcoind wallet required the user to run a bitcoind node. It was replaced with a bdk wallet which allows the user to connect to an electrum instance hosted remotely. An electrum and bitcoind testcontainer were created to the test the bdk wallet. The electrum container reads the blockdata from the bitcoind testcontainer through a shared volume. bitcoind-harness was removed as bitcoind initialisation code was moved into test_utils. The bdk wallet differs from the bitcoind wallet in that it needs to be manually synced with an electrum node. We synchronise the wallet once upon initialisation to prevent a potentially long running blocking task from interrupting protocol execution. The electrum HTTP API was used to get the latest block height and the transaction block height as this functionality was not present in the bdk wallet API or it required the bdk wallet to be re-synced to get an up to date value. |
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.github/workflows | ||
docs | ||
monero-harness | ||
swap | ||
.gitignore | ||
.mergify.yml | ||
bors.toml | ||
BTC_XMR_atomic_swap_protocol.svg | ||
Cargo.lock | ||
Cargo.toml | ||
LICENSE | ||
README.md | ||
rust-toolchain | ||
rustfmt.toml |
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:
- Alice and Bob exchange a set of addresses, keys, zero-knowledge proofs and signatures.
- 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 timet_1
by usingTx_cancel
andTx_refund
. If Bob doesn't refund after timet_1
, Alice can punish Bob for being inactive by first publishingTx_cancel
and, aftert_2
, spending the output usingTx_punish
. - 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. - 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
. - 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. - 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.
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 ofbitcoind
.monero
: module contains a test wallet by way ofmonero-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.