Merge pull request #247 from BitGo/BTC-3241-bip360-p2mr-fixed-script

feat: add P2MR fixed-script wallet integration

Author: lcovar

packages/wasm-utxo/js/fixedScriptWallet/chains.ts

@@ -8,7 +8,7 @@ import { FixedScriptWalletNamespace } from "../wasm/wasm_utxo.js";
 import type { OutputScriptType } from "./scriptType.js";
 
 /** All valid chain codes as a const tuple */
-export const chainCodes = [0, 1, 10, 11, 20, 21, 30, 31, 40, 41] as const;
+export const chainCodes = [0, 1, 10, 11, 20, 21, 30, 31, 40, 41, 360, 361] as const;
 
 /** A valid chain code value */
 export type ChainCode = (typeof chainCodes)[number];

packages/wasm-utxo/src/address/networks.rs

@@ -142,6 +142,7 @@ impl OutputScriptSupport {
             OutputScriptType::P2sh => true, // all networks support legacy scripts
             OutputScriptType::P2shP2wsh | OutputScriptType::P2wsh => self.segwit,
             OutputScriptType::P2trLegacy | OutputScriptType::P2trMusig2 => self.taproot,
+            OutputScriptType::P2mr => self.p2mr,
         }
     }
 }

packages/wasm-utxo/src/bip322/bitgo_psbt.rs

@@ -8,11 +8,12 @@ use crate::fixed_script_wallet::bitgo_psbt::{
     ProprietaryKeySubtype,
 };
 use crate::fixed_script_wallet::wallet_scripts::{
-    build_multisig_script_2_of_3, build_p2tr_ns_script, ScriptP2tr,
+    build_multisig_script_2_of_3, build_p2tr_ns_script, ScriptP2mr, ScriptP2tr,
 };
 use crate::fixed_script_wallet::{to_pub_triple, Chain, PubTriple, RootWalletKeys, WalletScripts};
 use crate::networks::Network;
 
+use miniscript::bitcoin::hashes::Hash;
 use miniscript::bitcoin::taproot::{LeafVersion, TapLeafHash};
 use miniscript::bitcoin::{Amount, ScriptBuf, Transaction, TxIn, TxOut};
 
@@ -140,6 +141,45 @@ pub fn add_bip322_input(
                 create_bip32_derivation(wallet_keys, chain, index);
             inner_psbt.inputs[input_index].witness_script = Some(script.witness_script.clone());
         }
+        WalletScripts::P2mr(script) => {
+            // P2MR is always script-path (no key-path). Same sighash as P2TR
+            // (BIP-360 reuses BIP-342 common signature message).
+            //
+            // Unlike P2trLegacy, we use the precomputed leaf hashes from ScriptP2mr
+            // rather than re-deriving keys and rebuilding scripts. The tree is fixed:
+            //   leaf[0]: user+bitgo  (key indices {0,2})
+            //   leaf[1]: user+backup (key indices {0,1})
+            //   leaf[2]: backup+bitgo (key indices {1,2})
+            //
+            // tap_scripts is skipped because P2MR control blocks (no internal key)
+            // can't be represented as rust-bitcoin's ControlBlock type.
+            let (signer_idx, cosigner_idx) =
+                sign_path.ok_or("signer and cosigner are required for p2mr inputs")?;
+
+            let mut pair = [signer_idx, cosigner_idx];
+            pair.sort();
+            let leaf_idx = match pair {
+                [0, 2] => 0,
+                [0, 1] => 1,
+                [1, 2] => 2,
+                _ => {
+                    return Err(format!(
+                        "Invalid signer pair: ({}, {})",
+                        signer_idx, cosigner_idx
+                    ))
+                }
+            };
+
+            let leaf_hash = TapLeafHash::from_byte_array(script.leaves[leaf_idx].leaf_hash);
+
+            inner_psbt.inputs[input_index].tap_key_origins = create_tap_bip32_derivation(
+                wallet_keys,
+                chain,
+                index,
+                &[signer_idx, cosigner_idx],
+                Some(leaf_hash),
+            );
+        }
         WalletScripts::P2trLegacy(script) | WalletScripts::P2trMusig2(script) => {
             // For taproot, sign_path is required
             let (signer_idx, cosigner_idx) =
@@ -428,7 +468,7 @@ pub fn verify_bip322_psbt_input(
 ///
 /// # Arguments
 /// * `pubkeys` - The three wallet pubkeys [user, backup, bitgo]
-/// * `script_type` - One of: "p2sh", "p2shP2wsh", "p2wsh", "p2tr", "p2trMusig2"
+/// * `script_type` - One of: "p2sh", "p2shP2wsh", "p2wsh", "p2tr", "p2trMusig2", "p2mr"
 ///
 /// # Returns
 /// The output script (scriptPubKey)
@@ -458,8 +498,12 @@ fn build_output_script_from_pubkeys(
             let script_p2tr = ScriptP2tr::new(pubkeys, true);
             Ok(script_p2tr.output_script())
         }
+        "p2mr" => {
+            let script_p2mr = ScriptP2mr::new(pubkeys);
+            Ok(script_p2mr.output_script())
+        }
         _ => Err(format!(
-            "Unknown script type '{}'. Expected: p2sh, p2shP2wsh, p2wsh, p2tr, p2trMusig2",
+            "Unknown script type '{}'. Expected: p2sh, p2shP2wsh, p2wsh, p2tr, p2trMusig2, p2mr",
             script_type
         )),
     }
@@ -537,7 +581,7 @@ fn verify_bip322_tx_structure(tx: &Transaction, input_index: usize) -> Result<()
 /// * `input_index` - The index of the input to verify
 /// * `message` - The message that was signed
 /// * `pubkeys` - The three wallet pubkeys [user, backup, bitgo]
-/// * `script_type` - One of: "p2sh", "p2shP2wsh", "p2wsh", "p2tr", "p2trMusig2"
+/// * `script_type` - One of: "p2sh", "p2shP2wsh", "p2wsh", "p2tr", "p2trMusig2", "p2mr"
 /// * `is_script_path` - For taproot types, whether script path was used (None for non-taproot)
 /// * `tag` - Optional custom tag for message hashing
 ///
@@ -614,7 +658,7 @@ pub fn verify_bip322_psbt_input_with_pubkeys(
 /// * `input_index` - The index of the input to verify
 /// * `message` - The message that was signed
 /// * `pubkeys` - The three wallet pubkeys [user, backup, bitgo]
-/// * `script_type` - One of: "p2sh", "p2shP2wsh", "p2wsh", "p2tr", "p2trMusig2"
+/// * `script_type` - One of: "p2sh", "p2shP2wsh", "p2wsh", "p2tr", "p2trMusig2", "p2mr"
 /// * `is_script_path` - For taproot types, whether script path was used (None for non-taproot)
 /// * `tag` - Optional custom tag for message hashing
 ///

packages/wasm-utxo/src/fixed_script_wallet/bitgo_psbt/mod.rs

@@ -1014,6 +1014,9 @@ impl BitGoPsbt {
                     create_bip32_derivation(wallet_keys, chain, derivation_index);
                 psbt_input.witness_script = Some(script.witness_script.clone());
             }
+            WalletScripts::P2mr(_) => {
+                return Err("P2MR PSBT input signing is not yet supported".to_string());
+            }
             WalletScripts::P2trLegacy(script) | WalletScripts::P2trMusig2(script) => {
                 let sign_path = options.sign_path.ok_or_else(|| {
                     "sign_path is required for p2tr/p2trMusig2 inputs".to_string()
@@ -1168,6 +1171,20 @@ impl BitGoPsbt {
                     create_bip32_derivation(wallet_keys, chain, derivation_index);
                 psbt_output.witness_script = Some(script.witness_script.clone());
             }
+            WalletScripts::P2mr(_) => {
+                // P2MR uses the same leaf structure as P2TR legacy (3 leaves, no musig2).
+                // We reuse taproot PSBT fields (tap_tree, tap_key_origins) since
+                // all tested PSBT parsers accept them on witness v2 outputs.
+                // No tap_internal_key (P2MR has no internal key or tweak).
+                psbt_output.tap_tree = Some(build_tap_tree_for_output(&pub_triple, false));
+                psbt_output.tap_key_origins = create_tap_bip32_derivation_for_output(
+                    wallet_keys,
+                    chain,
+                    derivation_index,
+                    &pub_triple,
+                    false,
+                );
+            }
             WalletScripts::P2trLegacy(script) | WalletScripts::P2trMusig2(script) => {
                 let is_musig2 = matches!(scripts, WalletScripts::P2trMusig2(_));
 

packages/wasm-utxo/src/fixed_script_wallet/bitgo_psbt/psbt_wallet_input.rs

@@ -751,6 +751,7 @@ pub enum InputScriptType {
     P2trLegacy,
     P2trMusig2ScriptPath,
     P2trMusig2KeyPath,
+    P2mr,
 }
 
 impl InputScriptType {
@@ -769,6 +770,7 @@ impl InputScriptType {
                     Ok(InputScriptType::P2trMusig2KeyPath)
                 }
             }
+            OutputScriptType::P2mr => Ok(InputScriptType::P2mr),
         }
     }