fix signal hash

package-lock.json

@@ -9,6 +9,9 @@
       "version": "0.1.2",
       "license": "ISC",
       "dependencies": {
+        "@ethersproject/bytes": "^5.7.0",
+        "@ethersproject/keccak256": "^5.7.0",
+        "@ethersproject/strings": "^5.7.0",
         "@faker-js/faker": "^8.0.2",
         "@prisma/client": "^5.0.0",
         "body-parser": "^1.20.2",

package.json

@@ -23,6 +23,9 @@
   "author": "",
   "license": "ISC",
   "dependencies": {
+    "@ethersproject/bytes": "^5.7.0",
+    "@ethersproject/keccak256": "^5.7.0",
+    "@ethersproject/strings": "^5.7.0",
     "@faker-js/faker": "^8.0.2",
     "@prisma/client": "^5.0.0",
     "body-parser": "^1.20.2",

src/crypto/signalHash.ts

@@ -0,0 +1,13 @@
+import { hexlify } from '@ethersproject/bytes';
+import { toUtf8Bytes } from '@ethersproject/strings';
+import { keccak256 } from '@ethersproject/keccak256';
+
+/**
+ * Hashes a signal string with Keccak256.
+ * @param signal The RLN signal.
+ * @returns The signal hash.
+ */
+export function calculateSignalHash(signal: string): bigint {
+  const converted = hexlify(toUtf8Bytes(signal));
+  return BigInt(keccak256(converted)) >> BigInt(8);
+}

src/crypto/verifier.ts

@@ -1,8 +1,8 @@
 import type { MessageI, RoomI } from 'discreetly-interfaces';
-import { str2BigInt } from 'discreetly-interfaces';
 import { RLNFullProof, RLNVerifier } from 'rlnjs';
 import vkey from './verification_key';
 import { Group } from '@semaphore-protocol/group';
+import { calculateSignalHash } from './signalHash';
 
 const v = new RLNVerifier(vkey);
 
@@ -16,7 +16,7 @@ async function verifyProof(msg: MessageI, room: RoomI, epochErrorRange = 5): Pro
   const rateLimit = room.rateLimit ? room.rateLimit : 1000;
   const currentEpoch = Math.floor(timestamp / rateLimit);
   const rlnIdentifier = BigInt(msg.roomId);
-  const msgHash = str2BigInt(msg.message);
+  const msgHash = calculateSignalHash(msg.message);
   let proof: RLNFullProof | undefined;
   // Check that the epoch falls within the range for the room
   const epoch = BigInt(msg.epoch);