diff --git a/BTC_XMR_atomic_swap_protocol.svg b/BTC_XMR_atomic_swap_protocol.svg new file mode 100644 index 00000000..63d794c0 --- /dev/null +++ b/BTC_XMR_atomic_swap_protocol.svg @@ -0,0 +1 @@ + \ No newline at end of file diff --git a/README.md b/README.md new file mode 100644 index 00000000..e9a2a1dc --- /dev/null +++ b/README.md @@ -0,0 +1,71 @@ +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](https://github.com/comit-network/xmr-btc-swap/blob/readme/BTC_XMR_atomic_swap_protocol.svg) + +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. + +- [bitcoin-harness](https://github.com/coblox/bitcoin-harness-rs) +- [monero-harness](https://github.com/comit-network/xmr-btc-swap/tree/master/monero-harness) + +These harnesses wrap interaction with `bitcoind` and `monerod`/`monero-wallet-rpc`. + +We use [testcontainers-rs](https://github.com/testcontainers/testcontainers-rs) to spin up `bitcoind`, `monerod`, and `monero-wallet-rpc` in docker containers during unit/integration testing. +