chore(gateway-contracts): user decrypt shares in events only (#845)

* chore(gateway-contracts): user decrypt shares in events only

Author: eudelins-zama

gateway-contracts/contracts/Decryption.sol

@@ -207,20 +207,13 @@ contract Decryption is
                 verifiedPublicDecryptSignatures;
         /// @notice Handles of the ciphertexts requested for a public decryption
         mapping(uint256 decryptionId => bytes32[] ctHandles) publicCtHandles;
+        /// @notice The number of public decryption requests, used to generate request IDs (`decryptionId`).
+        uint256 publicDecryptionCounter;
         // ----------------------------------------------------------------------------------------------
         // User decryption state variables:
         // ----------------------------------------------------------------------------------------------
-        /// @notice Verified signatures for a user decryption.
-        mapping(uint256 decryptionId => bytes[] verifiedSignatures) verifiedUserDecryptSignatures;
         /// @notice The decryption payloads stored during user decryption requests.
         mapping(uint256 decryptionId => UserDecryptionPayload payload) userDecryptionPayloads;
-        /// @notice The user decrypted shares received from user decryption responses.
-        mapping(uint256 decryptionId => bytes[] shares) userDecryptedShares;
-        // ----------------------------------------------------------------------------------------------
-        // Decryption counters:
-        // ----------------------------------------------------------------------------------------------
-        /// @notice The number of public decryption requests, used to generate request IDs (`decryptionId`).
-        uint256 publicDecryptionCounter;
         /// @notice The number of user decryption requests, used to generate request IDs (`decryptionId`)
         /// @notice (including delegated user decryption requests).
         uint256 userDecryptionCounter;
@@ -572,37 +565,34 @@ contract Decryption is
         /// @dev KMS node that has not already signed.
         _validateDecryptionResponseEIP712Signature(decryptionId, digest, signature);
 
-        /// @dev Store the signature for the user decryption response.
-        /// @dev This list is then used to check the consensus. Important: the mapping should not
-        /// @dev consider the digest (contrary to the public decryption case) as shares are expected
-        /// @dev to be different for each KMS node.
-        bytes[] storage verifiedSignatures = $.verifiedUserDecryptSignatures[decryptionId];
-        verifiedSignatures.push(signature);
-
-        /// @dev Store the user decrypted share for the user decryption response.
-        $.userDecryptedShares[decryptionId].push(userDecryptedShare);
-
         // Store the KMS transaction sender address for the public decryption response
         // It is important to consider the same mapping fields used for the consensus
         // A "late" valid KMS transaction sender address will still be added in the list.
         // We thus use a zero digest (default value for `bytes32`) to still be able to retrieve the
         // list later independently of the decryption response type (public or user).
-        $.consensusTxSenderAddresses[decryptionId][0].push(msg.sender);
+        address[] storage txSenderAddresses = $.consensusTxSenderAddresses[decryptionId][0];
+        txSenderAddresses.push(msg.sender);
+
+        // Store the user decrypted share for the user decryption response.
+        // The index of the share is the length of the txSenderAddresses - 1 so that the first response
+        // associated to this decryptionId has an index of 0.
+        emit UserDecryptionResponse(
+            decryptionId,
+            txSenderAddresses.length - 1,
+            userDecryptedShare,
+            signature,
+            extraData
+        );
 
         // Send the event if and only if the consensus is reached in the current response call.
         // This means a "late" response will not be reverted, just ignored and no event will be emitted
-        if (!$.decryptionDone[decryptionId] && _isConsensusReachedUser(verifiedSignatures.length)) {
+        if (!$.decryptionDone[decryptionId] && _isThresholdReachedUser(txSenderAddresses.length)) {
             $.decryptionDone[decryptionId] = true;
 
             // Since we use the default value for `bytes32`, this means we do not need to store the
             // digest in `decryptionConsensusDigest` here like we do for the public decryption case.
 
-            emit UserDecryptionResponse(
-                decryptionId,
-                $.userDecryptedShares[decryptionId],
-                verifiedSignatures,
-                extraData
-            );
+            emit UserDecryptionResponseThresholdReached(decryptionId);
         }
     }
 
@@ -867,20 +857,20 @@ contract Decryption is
             );
     }
 
-    /// @notice Checks if the consensus is reached among the KMS nodes.
-    /// @param kmsCounter The number of KMS nodes that agreed
-    /// @return Whether the consensus is reached
-    function _isConsensusReachedPublic(uint256 kmsCounter) internal view virtual returns (bool) {
-        uint256 consensusThreshold = GATEWAY_CONFIG.getPublicDecryptionThreshold();
-        return kmsCounter >= consensusThreshold;
+    /// @notice Indicates if the consensus is reached for public decryption.
+    /// @param numVerifiedResponses The number of public decryption responses that have been verified.
+    /// @return Whether the consensus has been reached
+    function _isConsensusReachedPublic(uint256 numVerifiedResponses) internal view virtual returns (bool) {
+        uint256 publicDecryptionThreshold = GATEWAY_CONFIG.getPublicDecryptionThreshold();
+        return numVerifiedResponses >= publicDecryptionThreshold;
     }
 
-    /// @notice Checks if the consensus for user decryption is reached among the KMS signers.
-    /// @param verifiedSignaturesCount The number of signatures that have been verified for a user decryption.
-    /// @return Whether the consensus is reached.
-    function _isConsensusReachedUser(uint256 verifiedSignaturesCount) internal view virtual returns (bool) {
-        uint256 consensusThreshold = GATEWAY_CONFIG.getUserDecryptionThreshold();
-        return verifiedSignaturesCount >= consensusThreshold;
+    /// @notice Indicates if the number of verified user decryption responses has reached the threshold.
+    /// @param numVerifiedResponses The number of user decryption responses that have been verified.
+    /// @return Whether the threshold has been reached.
+    function _isThresholdReachedUser(uint256 numVerifiedResponses) internal view virtual returns (bool) {
+        uint256 userDecryptionThreshold = GATEWAY_CONFIG.getUserDecryptionThreshold();
+        return numVerifiedResponses >= userDecryptionThreshold;
     }
 
     /// @notice Check the handles' conformance for public decryption requests.

gateway-contracts/contracts/interfaces/IDecryption.sol

@@ -78,17 +78,25 @@ interface IDecryption {
     /**
      * @notice Emitted when an public decryption response is made.
      * @param decryptionId The decryption request ID associated with the response.
-     * @param userDecryptedShares The list of decryption shares reencrypted with the user's public key.
-     * @param signatures The signatures of all the KMS connectors that responded.
+     * @param indexShare The index of the share associated with the decryption.
+     * @param userDecryptedShare The decryption share reencrypted with the user's public key.
+     * @param signature The signature of the KMS connector that responded.
      * @param extraData Generic bytes metadata for versioned payloads. First byte is for the version.
      */
     event UserDecryptionResponse(
         uint256 indexed decryptionId,
-        bytes[] userDecryptedShares,
-        bytes[] signatures,
+        uint256 indexShare,
+        bytes userDecryptedShare,
+        bytes signature,
         bytes extraData
     );
 
+    /**
+     * @notice Emitted when the number of user decryption response received reaches the threshold.
+     * @param decryptionId The decryption request ID.
+     */
+    event UserDecryptionResponseThresholdReached(uint256 indexed decryptionId);
+
     /// @notice Error indicating that the input list of handles is empty.
     error EmptyCtHandles();
 

gateway-contracts/contracts/mocks/DecryptionMock.sol

@@ -71,11 +71,14 @@ contract DecryptionMock {
 
     event UserDecryptionResponse(
         uint256 indexed decryptionId,
-        bytes[] userDecryptedShares,
-        bytes[] signatures,
+        uint256 indexShare,
+        bytes userDecryptedShare,
+        bytes signature,
         bytes extraData
     );
 
+    event UserDecryptionResponseThresholdReached(uint256 indexed decryptionId);
+
     uint256 publicDecryptionCounter = 1 << 248;
     uint256 userDecryptionCounter = 2 << 248;
 
@@ -137,9 +140,10 @@ contract DecryptionMock {
         bytes calldata signature,
         bytes calldata extraData
     ) external {
-        bytes[] memory userDecryptedShares = new bytes[](1);
-        bytes[] memory signatures = new bytes[](1);
+        uint256 indexShare;
+
+        emit UserDecryptionResponse(decryptionId, indexShare, userDecryptedShare, signature, extraData);
 
-        emit UserDecryptionResponse(decryptionId, userDecryptedShares, signatures, extraData);
+        emit UserDecryptionResponseThresholdReached(decryptionId);
     }
 }