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Bitcoin–Monero Cross-chain Atomic Swap
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Lucas Soriano del Pino 5daa3ea9a8 [WIP] Generate actions for Bob's on-chain protocol 
Mimics what @thomaseizinger did here [1] and here [2].

This has the advantage that the consumer has more freedom to execute
`Action`s without having to implement particular traits. The error
handling required inside this protocol-executing function is also
reduced.

As discussed with Thomas, for this approach to work well, the
trait functions such as `receive_transfer_proof` should be infallible,
and the implementer should be forced to hide IO errors behind a retry
mechanism.

All of these asynchronous calls need to be "raced" against
the abort condition (determined by the `refund_timelock`), which is
missing in the current state of the implementation.

The initial handshake of the protocol has not been included here,
because it may not be easy to integrate this approach with libp2p, but
a couple of messages still need to exchanged. I need @tcharding to
tell me if it's feasible/good to do it like this.

[1]
https://github.com/comit-network/comit-rs/blob/move-nectar-swap-to-comit/nectar/src/swap/comit/herc20_hbit.rs#L57-L184.
[2] e584d2b14f/nectar/src/swap.rs (L716-L751).
2020-10-13 10:53:20 +11:00
.github/workflows Add 60 sleep to workflow 2020-10-09 11:16:15 +11:00
monero-harness Remove redundant license 2020-09-28 17:18:02 +10:00
xmr-btc [WIP] Generate actions for Bob's on-chain protocol 2020-10-13 10:53:20 +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 Initial commit 2020-09-28 15:55:08 +10:00
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.