feat(sdk-coin-flrp): implement MPC support and enhance transaction signing methods

Ticket: CECHO-674

Author: mohd-kashif

modules/sdk-coin-flr/src/flr.ts

@@ -440,6 +440,11 @@ export class Flr extends AbstractEthLikeNewCoins {
    * @returns {Promise<BuildOptions>}
    */
   async getExtraPrebuildParams(buildParams: BuildOptions): Promise<BuildOptions> {
+    // MPC/TSS wallets don't use hop transactions — atomic tx is signed directly
+    if (buildParams.wallet?.multisigType() === 'tss') {
+      return {};
+    }
+
     if (
       !_.isUndefined(buildParams.hop) &&
       buildParams.hop &&

modules/sdk-coin-flr/test/unit/flr.ts

@@ -993,6 +993,19 @@ describe('flr', function () {
       const result = await tflrCoin.getExtraPrebuildParams(buildParams);
       result.should.have.property('hopParams');
     });
+
+    it('should return empty object for TSS wallets even when hop is true', async function () {
+      const tssWallet = new Wallet(bitgo, tflrCoin, { multisigType: 'tss' });
+      const buildParams = {
+        hop: true,
+        wallet: tssWallet,
+        recipients: [{ address: EXPORT_C_TEST_DATA.pMultisigAddress, amount: '100000000000000000' }],
+        type: 'Export' as const,
+      };
+
+      const result = await tflrCoin.getExtraPrebuildParams(buildParams);
+      result.should.deepEqual({});
+    });
   });
 
   describe('feeEstimate', function () {

modules/sdk-coin-flrp/src/flrp.ts

@@ -4,6 +4,7 @@ import {
   BaseCoin,
   BitGoBase,
   KeyPair,
+  MPCAlgorithm,
   MultisigType,
   multisigTypes,
   ParsedTransaction,
@@ -66,6 +67,16 @@ export class Flrp extends BaseCoin {
     return multisigTypes.onchain;
   }
 
+  /** @inheritdoc */
+  supportsTss(): boolean {
+    return true;
+  }
+
+  /** @inheritdoc */
+  getMPCAlgorithm(): MPCAlgorithm {
+    return 'ecdsa';
+  }
+
   async verifyTransaction(params: FlrpVerifyTransactionOptions): Promise<boolean> {
     const txHex = params.txPrebuild && params.txPrebuild.txHex;
     if (!txHex) {
@@ -232,13 +243,23 @@ export class Flrp extends BaseCoin {
     if (!this.isValidAddress(address)) {
       throw new InvalidAddressError(`invalid address: ${address}`);
     }
-    if (!keychains || keychains.length !== 3) {
-      throw new Error('Invalid keychains');
-    }
 
     // multisig addresses are separated by ~
     const splitAddresses = address.split('~');
 
+    // MPC/TSS: single address derived from common keychain
+    if (splitAddresses.length === 1 && keychains?.length === 1) {
+      const expectedAddr = new FlrpLib.KeyPair({ pub: keychains[0].pub }).getAddress(this._staticsCoin.network.type);
+      if (expectedAddr !== address) {
+        throw new UnexpectedAddressError(`address validation failure: ${address} is not of this wallet`);
+      }
+      return true;
+    }
+
+    if (!keychains || keychains.length !== 3) {
+      throw new Error('Invalid keychains');
+    }
+
     // derive addresses from keychain
     const unlockAddresses = keychains.map((keychain) =>
       new FlrpLib.KeyPair({ pub: keychain.pub }).getAddress(this._staticsCoin.network.type)
@@ -329,6 +350,29 @@ export class Flrp extends BaseCoin {
     return FlrpLib.Utils.isValidAddress(address);
   }
 
+  /**
+   * Get the raw bytes that need to be signed by the MPC ceremony.
+   * MPC.sign() internally SHA-256 hashes, so return raw unsigned tx bytes.
+   */
+  async getSignablePayload(txHex: string): Promise<Buffer> {
+    const txBuilder = this.getBuilder().from(txHex);
+    const tx = (await txBuilder.build()) as FlrpLib.Transaction;
+    return Buffer.from(tx.signablePayload);
+  }
+
+  /**
+   * Inject an MPC-produced signature into an unsigned transaction.
+   * @param txHex - Unsigned transaction hex
+   * @param signature - 65-byte ECDSA signature (r || s || recovery)
+   * @returns Signed transaction hex
+   */
+  async addSignatureToTransaction(txHex: string, signature: Buffer): Promise<string> {
+    const txBuilder = this.getBuilder().from(txHex);
+    const tx = await txBuilder.build();
+    (tx as FlrpLib.Transaction).addExternalSignature(new Uint8Array(signature));
+    return tx.toBroadcastFormat();
+  }
+
   /**
    * Signs Avaxp transaction
    */

modules/sdk-coin-flrp/src/lib/atomicTransactionBuilder.ts

@@ -136,6 +136,18 @@ export abstract class AtomicTransactionBuilder extends TransactionBuilder {
     const firstIndex = this.recoverSigner ? 2 : 0;
     const bitgoIndex = 1;
 
+    // MPC (threshold=1): single signing address
+    if (this.transaction._threshold === 1) {
+      if (this.transaction._fromAddresses.length < 1) {
+        throw new BuildTransactionError('Insufficient fromAddresses for MPC signing');
+      }
+      const addr = Buffer.from(this.transaction._fromAddresses[0]);
+      if (addr.length !== 20) {
+        throw new BuildTransactionError(`Invalid signing address length: expected 20 bytes, got ${addr.length}`);
+      }
+      return [addr];
+    }
+
     if (this.transaction._fromAddresses.length < Math.max(firstIndex, bitgoIndex) + 1) {
       throw new BuildTransactionError(
         `Insufficient fromAddresses: need at least ${Math.max(firstIndex, bitgoIndex) + 1} addresses`

modules/sdk-coin-flrp/src/lib/transaction.ts

@@ -241,6 +241,38 @@ export class Transaction extends BaseTransaction {
     }
   }
 
+  /**
+   * Apply an externally-produced signature (from MPC/TSS) to this transaction.
+   * Fills the first empty signature slot in each credential.
+   * @param signature - 65-byte Uint8Array (r[32] + s[32] + recovery[1])
+   */
+  addExternalSignature(signature: Uint8Array): void {
+    if (!this._flareTransaction) {
+      throw new InvalidTransactionError('empty transaction to sign');
+    }
+    if (!this.hasCredentials) {
+      throw new InvalidTransactionError('empty credentials to sign');
+    }
+    const unsignedTx = this._flareTransaction as UnsignedTx;
+
+    let signatureSet = false;
+    for (const credential of unsignedTx.credentials) {
+      const signatures = credential.getSignatures();
+      for (let i = 0; i < signatures.length; i++) {
+        if (isEmptySignature(signatures[i])) {
+          credential.setSignature(i, signature);
+          signatureSet = true;
+          break;
+        }
+      }
+    }
+
+    if (!signatureSet) {
+      throw new SigningError('No empty signature slot found');
+    }
+    this._rawSignedBytes = undefined;
+  }
+
   toBroadcastFormat(): string {
     if (!this._flareTransaction) {
       throw new InvalidTransactionError('Empty transaction data');

modules/sdk-coin-flrp/src/lib/transactionBuilder.ts

@@ -46,8 +46,8 @@ export abstract class TransactionBuilder extends BaseTransactionBuilder {
    * @param threshold - Number of required signatures
    */
   validateThreshold(threshold: number): void {
-    if (!threshold || threshold !== 2) {
-      throw new BuildTransactionError('Invalid transaction: threshold must be set to 2');
+    if (!threshold || (threshold !== 1 && threshold !== 2)) {
+      throw new BuildTransactionError('Invalid transaction: threshold must be 1 or 2');
     }
   }
 

modules/sdk-coin-flrp/test/unit/flrp.ts

@@ -8,7 +8,7 @@ import { EXPORT_IN_C } from '../resources/transactionData/exportInC';
 import { EXPORT_IN_P } from '../resources/transactionData/exportInP';
 import { IMPORT_IN_P } from '../resources/transactionData/importInP';
 import { IMPORT_IN_C } from '../resources/transactionData/importInC';
-import { HalfSignedAccountTransaction, TransactionType } from '@bitgo/sdk-core';
+import { HalfSignedAccountTransaction, TransactionType, MPCAlgorithm } from '@bitgo/sdk-core';
 import assert from 'assert';
 
 describe('Flrp test cases', function () {
@@ -57,6 +57,14 @@ describe('Flrp test cases', function () {
     basecoin.getDefaultMultisigType().should.equal('onchain');
   });
 
+  it('should support TSS', function () {
+    basecoin.supportsTss().should.equal(true);
+  });
+
+  it('should return ecdsa as MPC algorithm', function () {
+    (basecoin.getMPCAlgorithm() as MPCAlgorithm).should.equal('ecdsa');
+  });
+
   describe('Keypairs:', () => {
     it('should generate a keypair from random seed', function () {
       const keyPair = basecoin.generateKeyPair();
@@ -499,14 +507,39 @@ describe('Flrp test cases', function () {
       isValid.should.be.true();
     });
 
-    it('should throw for address with wrong number of keychains', async () => {
+    it('should verify MPC wallet address with single keychain', async () => {
+      const address = SEED_ACCOUNT.addressTestnet;
+
+      const isValid = await basecoin.isWalletAddress({
+        address,
+        keychains: [{ pub: SEED_ACCOUNT.publicKey }],
+      });
+
+      isValid.should.be.true();
+    });
+
+    it('should reject MPC wallet address that does not match keychain', async () => {
       const address = SEED_ACCOUNT.addressTestnet;
 
       await assert.rejects(
         async () =>
           basecoin.isWalletAddress({
             address,
-            keychains: [{ pub: SEED_ACCOUNT.publicKey }],
+            keychains: [{ pub: ACCOUNT_1.publicKey }],
+          }),
+        /address validation failure/
+      );
+    });
+
+    it('should throw for multisig address with wrong number of keychains', async () => {
+      // Two tilde-separated addresses but only 2 keychains
+      const address = SEED_ACCOUNT.addressTestnet + '~' + ACCOUNT_1.addressTestnet;
+
+      await assert.rejects(
+        async () =>
+          basecoin.isWalletAddress({
+            address,
+            keychains: [{ pub: SEED_ACCOUNT.publicKey }, { pub: ACCOUNT_1.publicKey }],
           }),
         /Invalid keychains/
       );