diff --git a/fix_3.py b/fix_3.py
new file mode 100644
index 0000000..e9a29c7
--- /dev/null
+++ b/fix_3.py
@@ -0,0 +1,23 @@
+// contracts/ListingRegistry.sol
+pragma solidity ^0.8.0;
+
+import "@openzeppelin/contracts/utils/cryptography/ECDSA.sol";
+
+contract ListingRegistry {
+    mapping(address => bool) public sellers;
+    mapping(uint256 => string) public listingMetadata;
+
+    function isValidSignature(bytes32 hash, bytes memory signature) public view returns (bool) {
+        address signer = ECDSA.recover(hash, signature);
+        return sellers[signer];
+    }
+
+    function addSeller(address seller) public {
+        sellers[seller] = true;
+    }
+
+    function createListing(uint256 listingId, string memory metadata, bytes memory signature) public {
+        require(isValidSignature(keccak256(abi.encodePacked(listingId, metadata)), signature), "Invalid signature");
+        listingMetadata[listingId] = metadata;
+    }
+}
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