feat(sdk-coin-flrp): add recoverySignature method for public key recovery from signature

Ticket: WIN-8068

feat(sdk-coin-flrp): enhance createSignature to return 65-byte signature with recovery parameter and add unit tests for recoverySignature

TICKET: WIN-8068

Author: mohd-kashif

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

@@ -118,11 +118,34 @@ export class Utils implements BaseUtils {
 
   /**
    * Creates a signature using the Flare network parameters
+   * Returns a 65-byte signature (64 bytes signature + 1 byte recovery parameter)
    */
   createSignature(network: FlareNetwork, message: Buffer, prv: Buffer): Buffer {
     const messageHash = this.sha256(message);
     const signature = ecc.sign(messageHash, prv);
-    return Buffer.from(signature);
+
+    // Get the public key from the private key for recovery parameter determination
+    const publicKey = ecc.pointFromScalar(prv, true);
+    if (!publicKey) {
+      throw new Error('Failed to derive public key from private key');
+    }
+
+    // Try recovery with param 0 and 1 to find the correct one
+    let recoveryParam = 0;
+    for (let i = 0; i <= 1; i++) {
+      const recovered = ecc.recoverPublicKey(messageHash, signature, i, true);
+      if (recovered && Buffer.from(recovered).equals(Buffer.from(publicKey))) {
+        recoveryParam = i;
+        break;
+      }
+    }
+
+    // Append recovery parameter to create 65-byte signature
+    const sigWithRecovery = Buffer.alloc(65);
+    Buffer.from(signature).copy(sigWithRecovery, 0);
+    sigWithRecovery[64] = recoveryParam;
+
+    return sigWithRecovery;
   }
 
   /**
@@ -338,6 +361,38 @@ export class Utils implements BaseUtils {
   flareIdString(value: string): Id {
     return new Id(Buffer.from(value, 'hex'));
   }
+
+  /**
+   * FlareJS wrapper to recover signature
+   * @param network
+   * @param message
+   * @param signature
+   * @return recovered public key
+   */
+  recoverySignature(network: FlareNetwork, message: Buffer, signature: Buffer): Buffer {
+    try {
+      // Hash the message first - must match the hash used in signing
+      const messageHash = createHash('sha256').update(message).digest();
+
+      // Extract recovery parameter and signature
+      if (signature.length !== 65) {
+        throw new Error('Invalid signature length - expected 65 bytes (64 bytes signature + 1 byte recovery)');
+      }
+
+      const recoveryParam = signature[64];
+      const sigOnly = signature.slice(0, 64);
+
+      // Recover public key using the provided recovery parameter
+      const recovered = ecc.recoverPublicKey(messageHash, sigOnly, recoveryParam, true);
+      if (!recovered) {
+        throw new Error('Failed to recover public key');
+      }
+
+      return Buffer.from(recovered);
+    } catch (error) {
+      throw new Error(`Failed to recover signature: ${error}`);
+    }
+  }
 }
 
 const utils = new Utils();

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

@@ -0,0 +1,73 @@
+import { coins, FlareNetwork } from '@bitgo/statics';
+import * as assert from 'assert';
+import { Utils } from '../../../src/lib/utils';
+
+describe('Utils', function () {
+  let utils: Utils;
+
+  beforeEach(function () {
+    utils = new Utils();
+  });
+
+  describe('recoverySignature', function () {
+    it('should recover public key from valid signature', function () {
+      const network = coins.get('flrp').network as FlareNetwork;
+      const message = Buffer.from('hello world', 'utf8');
+      const privateKey = Buffer.from('0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef', 'hex');
+
+      // Create signature using the same private key
+      const signature = utils.createSignature(network, message, privateKey);
+
+      // Recover public key
+      const recoveredPubKey = utils.recoverySignature(network, message, signature);
+
+      assert.ok(recoveredPubKey instanceof Buffer);
+      assert.strictEqual(recoveredPubKey.length, 33); // Should be compressed public key (33 bytes)
+    });
+
+    it('should recover same public key for same message and signature', function () {
+      const network = coins.get('flrp').network as FlareNetwork;
+      const message = Buffer.from('hello world', 'utf8');
+      const privateKey = Buffer.from('0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef', 'hex');
+      const signature = utils.createSignature(network, message, privateKey);
+
+      const pubKey1 = utils.recoverySignature(network, message, signature);
+      const pubKey2 = utils.recoverySignature(network, message, signature);
+
+      assert.deepStrictEqual(pubKey1, pubKey2);
+    });
+
+    it('should recover public key that matches original key', function () {
+      const network = coins.get('flrp').network as FlareNetwork;
+      const message = Buffer.from('hello world', 'utf8');
+      const privateKey = Buffer.from('0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef', 'hex');
+
+      // Get original public key
+      const { ecc } = require('@bitgo/secp256k1');
+      const originalPubKey = Buffer.from(ecc.pointFromScalar(privateKey, true) as Uint8Array);
+
+      // Create signature and recover public key
+      const signature = utils.createSignature(network, message, privateKey);
+      const recoveredPubKey = utils.recoverySignature(network, message, signature);
+
+      // Convert both to hex strings for comparison
+      assert.strictEqual(recoveredPubKey.toString('hex'), originalPubKey.toString('hex'));
+    });
+
+    it('should throw error for invalid signature', function () {
+      const network = coins.get('flrp').network as FlareNetwork;
+      const message = Buffer.from('hello world', 'utf8');
+      const invalidSignature = Buffer.from('invalid signature', 'utf8');
+
+      assert.throws(() => utils.recoverySignature(network, message, invalidSignature), /Failed to recover signature/);
+    });
+
+    it('should throw error for empty message', function () {
+      const network = coins.get('flrp').network as FlareNetwork;
+      const message = Buffer.alloc(0);
+      const signature = Buffer.alloc(65); // Empty but valid length signature (65 bytes: 64 signature + 1 recovery param)
+
+      assert.throws(() => utils.recoverySignature(network, message, signature), /Failed to recover signature/);
+    });
+  });
+});