Merge #682: Add a custom signer for hardware wallets

138acc3 Change `populate_test_db` to not return empty input (wszdexdrf)
d6e1dd1 Change CI to add test using ledger emulator (wszdexdrf)
7603477 Add a custom signer for hardware wallets (wszdexdrf)

Pull request description:

  Also adds a new test in CI for building and testing on a virtual
  hardware wallet.

  ### Description

  This PR would enable BDK users to sign transactions using a hardware wallet. It is just the beginning hence there are no complex features, but I hope not for long.
  I have added a test in CI for building a ledger emulator and running the new test on it. The test is similar to the one on bitcoindevkit/rust-hwi.

  ### Notes to the reviewers
  The PR is incomplete (and wouldn't work, as the rust-hwi in `cargo.toml` is pointing to a local crate, temporarily) as a small change is required in rust-hwi (bitcoindevkit/rust-hwi#42).

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

  #### New Features:

  * [x] I've added tests for the new feature
  * [x] I've added docs for the new feature
  * [x] I've updated `CHANGELOG.md`

ACKs for top commit:
  afilini:
    ACK 138acc3

Tree-SHA512: 54337f06247829242b4dc60f733346173d957de8e9f8b80beb91304d679cfb4e0e4db722c967469265a5b6ede2bd641ba5c089760391c671995dc30de37897de

Author: afilini

.github/workflows/cont_integration.yml

@@ -172,3 +172,32 @@ jobs:
         run: rustup update
       - name: Check fmt
         run: cargo fmt --all -- --config format_code_in_doc_comments=true --check
+
+  test_harware_wallet:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        rust:
+          - version: 1.60.0 # STABLE
+          - version: 1.56.1 # MSRV
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v3
+    - name: Build simulator image
+      run: docker build -t hwi/ledger_emulator ./ci -f ci/Dockerfile.ledger
+    - name: Run simulator image
+      run: docker run --name simulator --network=host hwi/ledger_emulator &
+    - name: Install Python
+      uses: actions/setup-python@v4
+      with:
+        python-version: '3.9'
+    - name: Install python dependencies
+      run: pip install hwi==2.1.1 protobuf==3.20.1
+    - name: Set default toolchain
+      run: rustup default ${{ matrix.rust.version }}
+    - name: Set profile
+      run: rustup set profile minimal
+    - name: Update toolchain
+      run: rustup update
+    - name: Test
+      run: cargo test --features test-hardware-signer

CHANGELOG.md

@@ -7,6 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 - Add capacity to create FeeRate from sats/kvbytes and sats/kwu.
 - Rename `as_sat_vb` to `as_sat_per_vb`. Move all `FeeRate` test to `types.rs`.
+- Add custom Harware Wallet Signer `HwiSigner` in `src/wallet/harwaresigner/` module.
 
 ## [v0.21.0] - [v0.20.0]
 

Cargo.toml

@@ -33,6 +33,7 @@ rocksdb = { version = "0.14", default-features = false, features = ["snappy"], o
 cc = { version = ">=1.0.64", optional = true }
 socks = { version = "0.3", optional = true }
 lazy_static = { version = "1.4", optional = true }
+hwi = { version = "0.2.2", optional = true }
 
 bip39 = { version = "1.0.1", optional = true }
 bitcoinconsensus = { version = "0.19.0-3", optional = true }
@@ -61,6 +62,7 @@ key-value-db = ["sled"]
 all-keys = ["keys-bip39"]
 keys-bip39 = ["bip39"]
 rpc = ["bitcoincore-rpc"]
+hardware-signer = ["hwi"]
 
 # We currently provide mulitple implementations of `Blockchain`, all are
 # blocking except for the `EsploraBlockchain` which can be either async or
@@ -93,6 +95,7 @@ test-rpc = ["rpc", "electrsd/electrs_0_8_10", "electrsd/bitcoind_22_0", "test-bl
 test-rpc-legacy = ["rpc", "electrsd/electrs_0_8_10", "electrsd/bitcoind_0_20_0", "test-blockchains"]
 test-esplora = ["electrsd/legacy", "electrsd/esplora_a33e97e1", "electrsd/bitcoind_22_0", "test-blockchains"]
 test-md-docs = ["electrum"]
+test-hardware-signer = ["hardware-signer"]
 
 [dev-dependencies]
 lazy_static = "1.4"

ci/Dockerfile.ledger

@@ -0,0 +1,9 @@
+# Taken from bitcoindevkit/rust-hwi
+FROM ghcr.io/ledgerhq/speculos
+
+RUN apt-get update
+RUN apt-get install wget -y
+RUN wget "https://github.com/LedgerHQ/speculos/blob/master/apps/nanos%23btc%232.1%231c8db8da.elf?raw=true" -O /speculos/btc.elf
+ADD automation.json /speculos/automation.json
+
+ENTRYPOINT ["python", "./speculos.py", "--automation", "file:automation.json", "--display", "headless", "--vnc-port", "41000", "btc.elf"]

ci/automation.json

@@ -0,0 +1,30 @@
+{
+    "version": 1,
+    "rules": [
+        {
+            "regexp": "Address \\(\\d/\\d\\)|Message hash \\(\\d/\\d\\)|Confirm|Fees|Review|Amount",
+            "actions": [
+                [ "button", 2, true ],
+                [ "button", 2, false ]
+            ]
+        },
+        {
+            "text": "Sign",
+            "conditions": [
+                [ "seen", false ]
+            ],
+            "actions": [
+                [ "button", 2, true ],
+                [ "button", 2, false ],
+                [ "setbool", "seen", true ]
+            ]
+        },
+        {
+            "regexp": "Approve|Sign|Accept",
+            "actions": [
+                [ "button", 3, true ],
+                [ "button", 3, false ]
+            ]
+        }
+    ]
+}

src/database/memory.rs

@@ -491,11 +491,10 @@ macro_rules! populate_test_db {
         let mut db = $db;
         let tx_meta = $tx_meta;
         let current_height: Option<u32> = $current_height;
-        let input = if $is_coinbase {
-            vec![$crate::bitcoin::TxIn::default()]
-        } else {
-            vec![]
-        };
+        let mut input = vec![$crate::bitcoin::TxIn::default()];
+        if !$is_coinbase {
+            input[0].previous_output.vout = 0;
+        }
         let tx = $crate::bitcoin::Transaction {
             version: 1,
             lock_time: 0,

src/wallet/hardwaresigner.rs

@@ -0,0 +1,64 @@
+// Bitcoin Dev Kit
+// Written in 2020 by Alekos Filini <[email protected]>
+//
+// Copyright (c) 2020-2021 Bitcoin Dev Kit Developers
+//
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+//! HWI Signer
+//!
+//! This module contains a simple implementation of a Custom signer for rust-hwi
+
+use bitcoin::psbt::PartiallySignedTransaction;
+use bitcoin::secp256k1::{All, Secp256k1};
+use bitcoin::util::bip32::Fingerprint;
+
+use hwi::error::Error;
+use hwi::types::{HWIChain, HWIDevice};
+use hwi::HWIClient;
+
+use crate::signer::{SignerCommon, SignerError, SignerId, TransactionSigner};
+
+#[derive(Debug)]
+/// Custom signer for Hardware Wallets
+///
+/// This ignores `sign_options` and leaves the decisions up to the hardware wallet.
+pub struct HWISigner {
+    fingerprint: Fingerprint,
+    client: HWIClient,
+}
+
+impl HWISigner {
+    /// Create a instance from the specified device and chain
+    pub fn from_device(device: &HWIDevice, chain: HWIChain) -> Result<HWISigner, Error> {
+        let client = HWIClient::get_client(device, false, chain)?;
+        Ok(HWISigner {
+            fingerprint: device.fingerprint,
+            client,
+        })
+    }
+}
+
+impl SignerCommon for HWISigner {
+    fn id(&self, _secp: &Secp256k1<All>) -> SignerId {
+        SignerId::Fingerprint(self.fingerprint)
+    }
+}
+
+/// This implementation ignores `sign_options`
+impl TransactionSigner for HWISigner {
+    fn sign_transaction(
+        &self,
+        psbt: &mut PartiallySignedTransaction,
+        _sign_options: &crate::SignOptions,
+        _secp: &crate::wallet::utils::SecpCtx,
+    ) -> Result<(), SignerError> {
+        psbt.combine(self.client.sign_tx(psbt)?.psbt)
+            .expect("Failed to combine HW signed psbt with passed PSBT");
+        Ok(())
+    }
+}

src/wallet/mod.rs

@@ -48,6 +48,9 @@ pub(crate) mod utils;
 #[cfg_attr(docsrs, doc(cfg(feature = "verify")))]
 pub mod verify;
 
+#[cfg(feature = "hardware-signer")]
+pub mod hardwaresigner;
+
 pub use utils::IsDust;
 
 #[allow(deprecated)]
@@ -5466,4 +5469,33 @@ pub(crate) mod test {
         // ...and checking that everything is fine
         assert_fee_rate!(psbt, details.fee.unwrap_or(0), fee_rate);
     }
+
+    #[cfg(feature = "test-hardware-signer")]
+    #[test]
+    fn test_create_signer() {
+        use crate::wallet::hardwaresigner::HWISigner;
+        use hwi::types::HWIChain;
+        use hwi::HWIClient;
+
+        let devices = HWIClient::enumerate().unwrap();
+        let device = devices.first().expect("No devices found");
+        let client = HWIClient::get_client(device, true, HWIChain::Regtest).unwrap();
+        let descriptors = client.get_descriptors(None).unwrap();
+        let custom_signer = HWISigner::from_device(device, HWIChain::Regtest).unwrap();
+
+        let (mut wallet, _, _) = get_funded_wallet(&descriptors.internal[0]);
+        wallet.add_signer(
+            KeychainKind::External,
+            SignerOrdering(200),
+            Arc::new(custom_signer),
+        );
+
+        let addr = wallet.get_address(LastUnused).unwrap();
+        let mut builder = wallet.build_tx();
+        builder.drain_to(addr.script_pubkey()).drain_wallet();
+        let (mut psbt, _) = builder.finish().unwrap();
+
+        let finalized = wallet.sign(&mut psbt, Default::default()).unwrap();
+        assert!(finalized);
+    }
 }

src/wallet/signer.rs

@@ -159,6 +159,16 @@ pub enum SignerError {
     InvalidSighash,
     /// Error while computing the hash to sign
     SighashError(sighash::Error),
+    /// Error while signing using hardware wallets
+    #[cfg(feature = "hardware-signer")]
+    HWIError(hwi::error::Error),
+}
+
+#[cfg(feature = "hardware-signer")]
+impl From<hwi::error::Error> for SignerError {
+    fn from(e: hwi::error::Error) -> Self {
+        SignerError::HWIError(e)
+    }
 }
 
 impl From<sighash::Error> for SignerError {