Merge rust-bitcoin#42: Fix bip32 usage in example

7e99ee0 Fix bip32 usage in example (Nick Johnson)

Pull request description:

  Supersedes rust-bitcoin#34

ACKs for top commit:
  tcharding:
    ACK 7e99ee0

Tree-SHA512: 50466c997d15d391a9625c6d087d99c47f05dd8cc4013a7e55101ac86cb829291f298ee4cbfd026babd461884ed6cd402d708d5f0c4f13d4d73f8f757b44ea0f

Author: tcharding

examples/v0.rs

@@ -7,7 +7,9 @@
 //! taken as NOT PROVEN CORRECT.
 
 use std::collections::BTreeMap;
+use std::str::FromStr;
 
+use psbt_v2::bitcoin::bip32::{DerivationPath, Fingerprint};
 use psbt_v2::bitcoin::hashes::Hash as _;
 use psbt_v2::bitcoin::locktime::absolute;
 use psbt_v2::bitcoin::opcodes::all::OP_CHECKMULTISIG;
@@ -86,6 +88,17 @@ fn main() -> anyhow::Result<()> {
     psbt.inputs[0].witness_utxo = Some(alice.input_utxo());
     psbt.inputs[1].witness_utxo = Some(bob.input_utxo());
 
+    // Add BIP32 derivation information for signing.
+    // Without this, psbt.sign() will not sign the inputs because bip32_sign_ecdsa() iterates
+    // over psbt.bip32_derivation to determine which keys should sign.
+    let fake_fp: [u8; 4] = [0; 4];
+    psbt.inputs[0]
+        .bip32_derivation
+        .insert(alice.0.pk, (Fingerprint::from(fake_fp), DerivationPath::from_str("m")?));
+    psbt.inputs[1]
+        .bip32_derivation
+        .insert(bob.0.pk, (Fingerprint::from(fake_fp), DerivationPath::from_str("m")?));
+
     // Since we are spending 2 p2wpkh inputs there are no other updates needed.
 
     // Each party signs a copy of the PSBT.