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

Ticket: WIN-8068

Author: mohd-kashif

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

@@ -338,6 +338,38 @@ 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();