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Bitcoin–Monero Cross-chain Atomic Swap
887 Commits 73 Branches 28 Tags 81 MiB
Rust 99.8%
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bors[bot] 20f2e56e2d
Merge #271 
271: Bob can verify that the XMR lock tx was published r=da-kami a=da-kami

The Monero `txhash` log was removed. I feel the user should have the possibility to verify that the transaction was actually published so I added the tx-hash to the confirmation output. 

We could potentially print the tx-hash when receiving the transfer proof already, but that might not add much value compared to printing it with the confirmations. 

Additionally we should allow the user to at least know when the XMR can be expected in the user's wallet, otherwise the swap ends like this:

```
2021-03-04 13:49:19   INFO Monero lock tx received 5 out of 5 confirmations
```

This is just not very informative - yes, the final transaction is an implementation detail, but I don't think we should hide the transactions from the user. By printing the tx-hash for spending from the lock-tx into the user wallet we ensure the user knows that the XMR can now be expected in the user wallet. 

--- 

To add context, here the complete log (with debug enabled) **before** this change: 

```
2021-03-04 13:30:46  DEBUG Database and seed will be stored in /Users/dakami/Library/Application Support/xmr-btc-swap
2021-03-04 13:30:46  DEBUG Starting monero-wallet-rpc on port 56145
2021-03-04 13:30:51  DEBUG Requesting quote
2021-03-04 13:30:51   INFO Received quote: 1 XMR = 0.00433500 BTC
2021-03-04 13:30:51   INFO Still got 0.01018746 BTC left in wallet, swapping ...
2021-03-04 13:30:51   INFO Spot price for 0.00500000 BTC is 1.153402537485 XMR
2021-03-04 13:30:52  DEBUG Starting execution setup with 12D3KooWCdMKjesXMJz1SiZ7HgotrxuqhQJbP5sgBm2BwP1cqThi
2021-03-04 13:30:55   INFO Published Bitcoin 3a6690a962191529892318819fb20e7f1ac4625400e64ee734056a9b2a17ad8f transaction as lock
2021-03-04 13:41:13  DEBUG Received Transfer Proof from 12D3KooWCdMKjesXMJz1SiZ7HgotrxuqhQJbP5sgBm2BwP1cqThi
2021-03-04 13:42:11   INFO Monero lock tx received 1 out of 5 confirmations
2021-03-04 13:45:33   INFO Monero lock tx received 2 out of 5 confirmations
2021-03-04 13:47:49   INFO Monero lock tx received 3 out of 5 confirmations
2021-03-04 13:48:56   INFO Monero lock tx received 4 out of 5 confirmations
2021-03-04 13:49:19   INFO Monero lock tx received 5 out of 5 confirmations
2021-03-04 13:49:19  DEBUG Encrypted signature sent
2021-03-04 13:49:19  DEBUG Alice acknowledged encrypted signature
2021-03-04 13:49:19  DEBUG watching for tx: e5569d3f0bcccac95252dffaebe74ead0360c09b76bc762de890aaa0e51afbcf
2021-03-04 13:49:20  DEBUG Received protocol error "missing transaction" from Electrum, retrying...
2021-03-04 13:49:22  DEBUG Received protocol error "missing transaction" from Electrum, retrying...
```



Co-authored-by: Daniel Karzel <daniel@comit.network>
2021-03-04 06:24:59 +00:00
.github/workflows Reduce workflow duplication 2021-03-04 15:43:15 +11:00
docs The first message is actually a quote or rate request 2021-02-12 17:05:06 +11:00
monero-harness No prefix for wallets in monero harness 2021-03-03 17:03:34 +11:00
monero-rpc Remove Arcs in favour of references 2021-03-03 17:23:07 +11:00
swap Merge #271 2021-03-04 06:24:59 +00:00
tokio-tar Download and run monero wallet rpc on swap cli startup 2021-02-25 11:21:41 +11:00
.gitignore Push cargo lock to git as we are building a binary 2020-12-01 09:31:41 +11:00
.mergify.yml Add Mergify rule to delete merged branch and bors+ 2020-12-21 16:09:21 +11:00
bors.toml Add windows to release and build workflow 2021-03-02 15:09:12 +11:00
BTC_XMR_atomic_swap_protocol.svg Fix embedded image 2020-10-09 09:45:48 +11:00
Cargo.lock Add windows support to monero rpc installer 2021-03-02 15:09:12 +11:00
Cargo.toml Split monero-harness into harness and rpc 2021-02-23 14:30:20 +11:00
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 Update rust-toolchain to new toml syntax 2021-02-18 13:16:05 +11:00
rustfmt.toml Change imports_granularity to module 2021-03-04 14:48:13 +11:00

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.