From a1c8f6e907163d8195dda24bb2a49ac9c376430d Mon Sep 17 00:00:00 2001
From: Arseniy Klempner <arseniyk@status.im>
Date: Mon, 27 Oct 2025 13:45:59 -0700
Subject: [PATCH] fix: convert bigint to string when serializing membership

---
 packages/rln/src/keystore/keystore.ts | 47 +++++++++++++++++++--------
 1 file changed, 33 insertions(+), 14 deletions(-)

diff --git a/packages/rln/src/keystore/keystore.ts b/packages/rln/src/keystore/keystore.ts
index f001f2938d..c2623b2fa0 100644
--- a/packages/rln/src/keystore/keystore.ts
+++ b/packages/rln/src/keystore/keystore.ts
@@ -160,7 +160,15 @@ export class Keystore {
   }
 
   public toString(): string {
-    return JSON.stringify(this.data);
+    // Custom replacer function to handle BigInt serialization
+    const bigIntReplacer = (_key: string, value: unknown): unknown => {
+      if (typeof value === "bigint") {
+        return value.toString();
+      }
+      return value;
+    };
+
+    return JSON.stringify(this.data, bigIntReplacer);
   }
 
   public toObject(): NwakuKeystore {
@@ -327,21 +335,32 @@ export class Keystore {
     const { IDCommitment, IDNullifier, IDSecretHash, IDTrapdoor } =
       options.identity;
 
+    // Custom replacer function to handle BigInt serialization
+    const bigIntReplacer = (_key: string, value: unknown): unknown => {
+      if (typeof value === "bigint") {
+        return value.toString();
+      }
+      return value;
+    };
+
     return utf8ToBytes(
-      JSON.stringify({
-        treeIndex: options.membership.treeIndex,
-        identityCredential: {
-          idCommitment: Array.from(IDCommitment),
-          idNullifier: Array.from(IDNullifier),
-          idSecretHash: Array.from(IDSecretHash),
-          idTrapdoor: Array.from(IDTrapdoor)
+      JSON.stringify(
+        {
+          treeIndex: options.membership.treeIndex,
+          identityCredential: {
+            idCommitment: Array.from(IDCommitment),
+            idNullifier: Array.from(IDNullifier),
+            idSecretHash: Array.from(IDSecretHash),
+            idTrapdoor: Array.from(IDTrapdoor)
+          },
+          membershipContract: {
+            chainId: options.membership.chainId,
+            address: options.membership.address
+          },
+          userMessageLimit: options.membership.rateLimit
         },
-        membershipContract: {
-          chainId: options.membership.chainId,
-          address: options.membership.address
-        },
-        userMessageLimit: options.membership.rateLimit
-      })
+        bigIntReplacer
+      )
     );
   }
 }