feat: move out_hash inside tx_effect_hash (#7489)

In the base rollup circuit, we currently sha hash l2 to l1 messages twice: - In tree form, to create each tx's `out_hash` - Flattened inside the `tx_effect_hash` This PR takes the `out_hash` and inserts it into the `tx_effect_hash` preimage, to prevent doubling sha hashing. This saves approx 18k gates in base. It increases the gas cost (TBC) as we now have to calculate each tx's `out_hash` on-chain. Note that to maintain simplicity of empty blocks/txs, an `out_hash` for a tx with no l2 to l1 messages is now **zero** (not H(0, 0) as previously).
AztecProtocol · Aug 20, 2024 · ff0effe · ff0effe
1 parent ec03e40
commit ff0effe
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Showing 14 changed files with 198 additions and 74 deletions.
diff --git a/l1-contracts/src/core/libraries/decoders/TxsDecoder.sol b/l1-contracts/src/core/libraries/decoders/TxsDecoder.sol
@@ -76,6 +76,7 @@ library TxsDecoder {
     bytes32 noteEncryptedLogsHash;
     bytes32 encryptedLogsHash;
     bytes32 unencryptedLogsHash;
+    bytes32 txOutHash;
   }
 
   /**
@@ -105,7 +106,7 @@ library TxsDecoder {
          *    transactionFee,
          *    noteHashesKernel,
          *    nullifiersKernel,
-         *    l2ToL1MsgsKernel,
+         *    txOutHash,                                           |=> Computed below from l2tol1msgs
          *    publicDataUpdateRequestsKernel,
          *    noteEncryptedLogsLength,
          *    encryptedLogsLength,
@@ -179,6 +180,8 @@ library TxsDecoder {
         // UNENCRYPTED LOGS HASH
         (vars.unencryptedLogsHash, offset, vars.kernelUnencryptedLogsLength) =
           computeKernelUnencryptedLogsHash(offset, _body);
+        // TX LEVEL OUT HASH
+        (vars.txOutHash) = computeTxOutHash(offsets.l2ToL1Msgs, _body);
 
         // We throw to ensure that the byte len we charge for DA gas in the kernels matches the actual chargable log byte len
         // Without this check, the user may provide the kernels with a lower log len than reality
@@ -230,12 +233,7 @@ library TxsDecoder {
               counts.nullifier * 0x20,
               Constants.NULLIFIERS_NUM_BYTES_PER_BASE_ROLLUP
             ),
-            sliceAndPadRight(
-              _body,
-              offsets.l2ToL1Msgs,
-              counts.l2ToL1Msgs * 0x20,
-              Constants.L2_TO_L1_MSGS_NUM_BYTES_PER_BASE_ROLLUP
-            ),
+            vars.txOutHash,
             sliceAndPadRight(
               _body,
               offsets.publicData,
@@ -257,7 +255,7 @@ library TxsDecoder {
       // We pad base leaves with hashes of empty tx effect.
       for (uint256 i = numTxEffects; i < vars.baseLeaves.length; i++) {
         // Value taken from tx_effect.test.ts "hash of empty tx effect matches snapshot" test case
-        vars.baseLeaves[i] = hex"00e8b31e302d11fbf7da124b537ba2d44f88e165da03c6557e2b0f6dc486e025";
+        vars.baseLeaves[i] = hex"00f0aa51fc81f8242316fcf2cb3b28196241ed3fa26dd320a959bce6c529b270";
       }
     }
 
@@ -518,7 +516,7 @@ library TxsDecoder {
 
   /**
    * @notice Computes the root for a binary unbalanced Merkle-tree given the leaves.
-   * @dev Filled in greedily with subtrees. Useful for txsEffectHash and outHash tree.
+   * @dev Filled in greedily with subtrees. Useful for txsEffectsHash and outHash tree.
    * @param _leaves - The 32 bytes leafs to build the tree of.
    * @return The root of the Merkle tree.
    */
@@ -550,6 +548,27 @@ library TxsDecoder {
     return root;
   }
 
+  /**
+   * @notice Computes the root for the binary variable height Merkle-tree made of one tx's L2 to L1 msgs.
+   * @dev Mimics compute_kernel_out_hash in base_rollup.
+   * TODO(#7218): Revert to fixed height tree for outbox
+   * @param _data - The blob of data containing l2 to l1 msgs.
+   * @return The root of the Merkle tree.
+   */
+  function computeTxOutHash(uint256 _start, bytes calldata _data) internal pure returns (bytes32) {
+    uint256 offset = _start;
+    // The stored offsets.l2ToL1Msgs does not include the single byte storing the num of msgs, hence -1
+    uint32 numMsgs = uint32(read1(_data, _start - 1));
+    uint256 numMsgsToPad = computeNumMsgsToPad(uint32(numMsgs));
+    bytes32[] memory leavesInMsgTree = new bytes32[](numMsgs + numMsgsToPad);
+    for (uint256 i = 0; i < numMsgs; i++) {
+      leavesInMsgTree[i] = bytes32(slice(_data, offset, 0x20));
+      offset += 0x20;
+    }
+    bytes32 outHash = computeRoot(leavesInMsgTree);
+    return outHash;
+  }
+
   /**
    * @notice Wrapper around the slicing to avoid some stack too deep
    * @param _data - The data to slice
@@ -619,6 +638,32 @@ library TxsDecoder {
     return uint256(uint32(bytes4(slice(_data, _offset, 4))));
   }
 
+  /**
+   * @notice Pads L2 to L1 messages to the next power of 2 - simple algo as we only have a max of 8 msgs
+   * @param _numL2toL1Msgs - num of msgs (currently between 0 and MAX_L2_TO_L1_MSGS_PER_TX = 8)
+   * @return Num msgs to pad
+   */
+  function computeNumMsgsToPad(uint32 _numL2toL1Msgs) internal pure returns (uint32) {
+    // We handle the edge case of 0 msgs by padding by 1 - this ensures computeRoot() gives a result of 0
+    if (_numL2toL1Msgs == 0 || _numL2toL1Msgs == 1) {
+      return 1;
+    }
+
+    uint32 v = _numL2toL1Msgs;
+
+    // the following rounds _numL2toL1Msgs up to the next power of 2 (works only for 4 bytes value!)
+    v--;
+    v |= v >> 1;
+    v |= v >> 2;
+    v |= v >> 4;
+    // We dont expect to have MAX_L2_TO_L1_MSGS_PER_TX greater than 8 bits, so commented out the below to save gas
+    // v |= v >> 8;
+    // v |= v >> 16;
+    v++;
+
+    return v - _numL2toL1Msgs;
+  }
+
   function computeNumTxEffectsToPad(uint32 _numTxEffects) internal pure returns (uint32) {
     // 2 is the minimum number of tx effects so we have to handle the following 2 cases separately
     if (_numTxEffects == 0) {

diff --git a/l1-contracts/test/Rollup.t.sol b/l1-contracts/test/Rollup.t.sol
@@ -414,9 +414,9 @@ contract RollupTest is DecoderBase {
       // The below is a little janky - we know that this test deals with full txs with equal numbers
       // of msgs or txs with no messages, so the division works
       // TODO edit full.messages to include information about msgs per tx?
-      uint256 subTreeHeight = merkleTestUtil.calculateTreeHeightFromSize(
-        full.messages.l2ToL1Messages.length == 0 ? 0 : full.messages.l2ToL1Messages.length / numTxs
-      );
+      uint256 subTreeHeight = full.messages.l2ToL1Messages.length == 0
+        ? 0
+        : merkleTestUtil.calculateTreeHeightFromSize(full.messages.l2ToL1Messages.length / numTxs);
       uint256 outHashTreeHeight = merkleTestUtil.calculateTreeHeightFromSize(numTxs);
       uint256 numMessagesWithPadding = numTxs * Constants.MAX_L2_TO_L1_MSGS_PER_TX;
 

diff --git a/l1-contracts/test/decoders/Decoders.t.sol b/l1-contracts/test/decoders/Decoders.t.sol
@@ -319,6 +319,21 @@ contract DecodersTest is DecoderBase {
     assertEq(logsHash, referenceLogsHashFromIteration3, "Incorrect logs hash");
   }
 
+  function testComputeTxOutHash() public {
+    // A tx with no msgs should give an out hash of 0
+    bytes memory encodedMsgs = abi.encodePacked(hex"00");
+    bytes32 outHash = txsHelper.computeTxOutHash(encodedMsgs);
+    assertEq(outHash, 0, "Incorrect tx empty out hash");
+    // Mimics test_3_elems test in .nr, with msg hashes of value 10, 11, and 12
+    bytes32[3] memory msgs = [bytes32(hex"0a"), bytes32(hex"0b"), bytes32(hex"0c")];
+    encodedMsgs = abi.encodePacked(hex"03", msgs);
+    outHash = txsHelper.computeTxOutHash(encodedMsgs);
+    bytes32 firstNode = Hash.sha256ToField(bytes.concat(msgs[0], msgs[1]));
+    bytes32 secondNode = Hash.sha256ToField(bytes.concat(msgs[2], bytes32(0)));
+    bytes32 expectedOutHash = Hash.sha256ToField(bytes.concat(firstNode, secondNode));
+    assertEq(outHash, expectedOutHash, "Incorrect tx out hash");
+  }
+
   function testTxsDecoderCorrectlyComputesNumTxEffectsToPad() public {
     // Minimum num txs is 2 so when there are no real txs we need to pad to 2
     uint32 numTxEffects = 0;
@@ -337,4 +352,42 @@ contract DecodersTest is DecoderBase {
     paddedNumTxEffects = txsHelper.computeNumTxEffectsToPad(numTxEffects);
     assertEq(paddedNumTxEffects, 0, "Incorrect number of tx effects to pad");
   }
+
+  function testTxsDecoderCorrectlyComputesNumMsgsToPad() public {
+    uint32 numMsgs = 0;
+    uint32 numMsgsToPad = txsHelper.computeNumMsgsToPad(numMsgs);
+    assertEq(numMsgsToPad, 1, "Incorrect number of msgs to pad");
+
+    numMsgs = 1;
+    numMsgsToPad = txsHelper.computeNumMsgsToPad(numMsgs);
+    assertEq(numMsgsToPad, 2 ** 1 - numMsgs, "Incorrect number of msgs to pad");
+
+    numMsgs = 2;
+    numMsgsToPad = txsHelper.computeNumMsgsToPad(numMsgs);
+    assertEq(numMsgsToPad, 0, "Incorrect number of msgs to pad");
+
+    numMsgs = 3;
+    numMsgsToPad = txsHelper.computeNumMsgsToPad(numMsgs);
+    assertEq(numMsgsToPad, 2 ** 2 - numMsgs, "Incorrect number of msgs to pad");
+
+    numMsgs = 4;
+    numMsgsToPad = txsHelper.computeNumMsgsToPad(numMsgs);
+    assertEq(numMsgsToPad, 0, "Incorrect number of msgs to pad");
+
+    numMsgs = 5;
+    numMsgsToPad = txsHelper.computeNumMsgsToPad(numMsgs);
+    assertEq(numMsgsToPad, 2 ** 3 - numMsgs, "Incorrect number of msgs to pad");
+
+    numMsgs = 6;
+    numMsgsToPad = txsHelper.computeNumMsgsToPad(numMsgs);
+    assertEq(numMsgsToPad, 2 ** 3 - numMsgs, "Incorrect number of msgs to pad");
+
+    numMsgs = 7;
+    numMsgsToPad = txsHelper.computeNumMsgsToPad(numMsgs);
+    assertEq(numMsgsToPad, 2 ** 3 - numMsgs, "Incorrect number of msgs to pad");
+
+    numMsgs = 7;
+    numMsgsToPad = txsHelper.computeNumMsgsToPad(numMsgs);
+    assertEq(numMsgsToPad, 2 ** 3 - numMsgs, "Incorrect number of msgs to pad");
+  }
 }
diff --git a/l1-contracts/test/decoders/helpers/TxsDecoderHelper.sol b/l1-contracts/test/decoders/helpers/TxsDecoderHelper.sol
@@ -19,10 +19,18 @@ contract TxsDecoderHelper {
     return TxsDecoder.computeKernelEncryptedLogsHash(0, _kernelLogs);
   }
 
+  function computeTxOutHash(bytes calldata _kernelMsgs) external pure returns (bytes32) {
+    return TxsDecoder.computeTxOutHash(1, _kernelMsgs);
+  }
+
   function computeNumTxEffectsToPad(uint32 _numTxEffects) external pure returns (uint32) {
     return TxsDecoder.computeNumTxEffectsToPad(_numTxEffects);
   }
 
+  function computeNumMsgsToPad(uint32 _numL2toL1Msgs) external pure returns (uint32) {
+    return TxsDecoder.computeNumMsgsToPad(_numL2toL1Msgs);
+  }
+
   function computeUnbalancedRoot(bytes32[] memory _leaves) external pure returns (bytes32) {
     return TxsDecoder.computeUnbalancedRoot(_leaves);
   }

diff --git a/l1-contracts/test/fixtures/empty_block_1.json b/l1-contracts/test/fixtures/empty_block_1.json
@@ -8,24 +8,24 @@
     "l2ToL1Messages": []
   },
   "block": {
-    "archive": "0x0a5e13310d0c5b768e262a51b698d6aa3fb7f45e5d64708d7d3bfc3e8d3fc64a",
+    "archive": "0x0b97584f2e175ce708df94c14fee5e53d1c92cd5308346c6eabb79005ccf6733",
     "body": "0x00000000",
-    "txsEffectsHash": "0x00d09e7feff5a1049661763ded52742f02aac5d9793b27a40d6b9c60a668bdf2",
+    "txsEffectsHash": "0x00e994e16b3763fd5039413cf99c2b3c378e2bab939e7992a77bd201b28160d6",
     "decodedHeader": {
       "contentCommitment": {
         "inHash": "0x00089a9d421a82c4a25f7acbebe69e638d5b064fa8a60e018793dcb0be53752c",
-        "outHash": "0x0007638bb56b6dda2b64b8f76841114ac3a87a1820030e2e16772c4d294879c3",
+        "outHash": "0x00f5a5fd42d16a20302798ef6ed309979b43003d2320d9f0e8ea9831a92759fb",
         "numTxs": 2,
-        "txsEffectsHash": "0x00d09e7feff5a1049661763ded52742f02aac5d9793b27a40d6b9c60a668bdf2"
+        "txsEffectsHash": "0x00e994e16b3763fd5039413cf99c2b3c378e2bab939e7992a77bd201b28160d6"
       },
       "globalVariables": {
         "blockNumber": 1,
         "slotNumber": "0x0000000000000000000000000000000000000000000000000000000000000005",
         "chainId": 31337,
-        "timestamp": 1723019086,
+        "timestamp": 1723460388,
         "version": 1,
-        "coinbase": "0x6e255429b3eecd76bc5123d4539de205bfc8ed04",
-        "feeRecipient": "0x3020f3cce26a2e314fa3cade1dc808c87e6deab7b1c90a86c383428189c062b1",
+        "coinbase": "0x92c3bc662a41b5406370e6e30b6e4541c9c223e3",
+        "feeRecipient": "0x2af4d139729812fa69edfc27fc2d19b3d2616c9e4ec2313efb66fb2f234d59da",
         "gasFees": {
           "feePerDaGas": 0,
           "feePerL2Gas": 0
@@ -56,8 +56,8 @@
         }
       }
     },
-    "header": "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",
-    "publicInputsHash": "0x00e3c26b1e5dbca4734754e663ec588ed9e101588a8ece487c82934f559cfedd",
+    "header": "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",
+    "publicInputsHash": "0x00330b9ccec92816ea3dd5fefce65cdb3803cf663cf2959f403501ff1f27a73c",
     "numTxs": 0
   }
 }
diff --git a/l1-contracts/test/fixtures/empty_block_2.json b/l1-contracts/test/fixtures/empty_block_2.json
@@ -8,32 +8,32 @@
     "l2ToL1Messages": []
   },
   "block": {
-    "archive": "0x2b5b19f8f6282401f17498335c43653551c57ff4b1bd98d00d1429d79c50d293",
+    "archive": "0x1d77208270a6eca3c2b56adaad130b28e2fa111d6bc325ce3cc52b6a68f4894f",
     "body": "0x00000000",
-    "txsEffectsHash": "0x00d09e7feff5a1049661763ded52742f02aac5d9793b27a40d6b9c60a668bdf2",
+    "txsEffectsHash": "0x00e994e16b3763fd5039413cf99c2b3c378e2bab939e7992a77bd201b28160d6",
     "decodedHeader": {
       "contentCommitment": {
         "inHash": "0x00089a9d421a82c4a25f7acbebe69e638d5b064fa8a60e018793dcb0be53752c",
-        "outHash": "0x0007638bb56b6dda2b64b8f76841114ac3a87a1820030e2e16772c4d294879c3",
+        "outHash": "0x00f5a5fd42d16a20302798ef6ed309979b43003d2320d9f0e8ea9831a92759fb",
         "numTxs": 2,
-        "txsEffectsHash": "0x00d09e7feff5a1049661763ded52742f02aac5d9793b27a40d6b9c60a668bdf2"
+        "txsEffectsHash": "0x00e994e16b3763fd5039413cf99c2b3c378e2bab939e7992a77bd201b28160d6"
       },
       "globalVariables": {
         "blockNumber": 2,
         "slotNumber": "0x0000000000000000000000000000000000000000000000000000000000000006",
         "chainId": 31337,
-        "timestamp": 1723019098,
+        "timestamp": 1723460400,
         "version": 1,
-        "coinbase": "0x6e255429b3eecd76bc5123d4539de205bfc8ed04",
-        "feeRecipient": "0x3020f3cce26a2e314fa3cade1dc808c87e6deab7b1c90a86c383428189c062b1",
+        "coinbase": "0x92c3bc662a41b5406370e6e30b6e4541c9c223e3",
+        "feeRecipient": "0x2af4d139729812fa69edfc27fc2d19b3d2616c9e4ec2313efb66fb2f234d59da",
         "gasFees": {
           "feePerDaGas": 0,
           "feePerL2Gas": 0
         }
       },
       "lastArchive": {
         "nextAvailableLeafIndex": 2,
-        "root": "0x0a5e13310d0c5b768e262a51b698d6aa3fb7f45e5d64708d7d3bfc3e8d3fc64a"
+        "root": "0x0b97584f2e175ce708df94c14fee5e53d1c92cd5308346c6eabb79005ccf6733"
       },
       "stateReference": {
         "l1ToL2MessageTree": {
@@ -56,8 +56,8 @@
         }
       }
     },
-    "header": "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",
-    "publicInputsHash": "0x009806b2a395a75e618221b9a39c98be96c7a4053616894d9bc92bbd35c92eb0",
+    "header": "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",
+    "publicInputsHash": "0x006ccf0ce5551a2a07b16c10a4b208bd30403231409d44cedac9b6d489b9f212",
     "numTxs": 0
   }
 }
diff --git a/l1-contracts/test/fixtures/mixed_block_1.json b/l1-contracts/test/fixtures/mixed_block_1.json
diff --git a/l1-contracts/test/fixtures/mixed_block_2.json b/l1-contracts/test/fixtures/mixed_block_2.json
diff --git a/noir-projects/noir-protocol-circuits/crates/rollup-lib/src/base/base_rollup_inputs.nr b/noir-projects/noir-protocol-circuits/crates/rollup-lib/src/base/base_rollup_inputs.nr
@@ -132,14 +132,14 @@ impl BaseRollupInputs {
         let siloed_l2_to_l1_msgs = self.kernel_data.public_inputs.end.l2_to_l1_msgs.map(
             |message: ScopedL2ToL1Message| silo_l2_to_l1_message(message, self.kernel_data.public_inputs.constants.tx_context.version, self.kernel_data.public_inputs.constants.tx_context.chain_id)
         );
+        let out_hash = compute_kernel_out_hash(siloed_l2_to_l1_msgs);
         let tx_effects_hash = compute_tx_effects_hash(
             self.kernel_data.public_inputs.end,
             self.kernel_data.public_inputs.revert_code,
             transaction_fee,
             all_public_data_update_requests,
-            siloed_l2_to_l1_msgs
+            out_hash
         );
-        let out_hash = compute_kernel_out_hash(siloed_l2_to_l1_msgs);
 
         // Perform membership checks that the notes provided exist within the historical trees data
         self.perform_archive_membership_checks();
@@ -1084,12 +1084,7 @@ mod tests {
     #[test]
     unconstrained fn empty_block_out_hash() {
         let outputs = BaseRollupInputsBuilder::new().execute();
-        // For now setting an empty out hash to be H(0,0) to keep consistent
-        // with prev work.
-        let hash_input_flattened = [0; 64];
-        let sha_digest = std::hash::sha256(hash_input_flattened);
-        let expected_out_hash = field_from_bytes_32_trunc(sha_digest);
-        assert_eq(outputs.out_hash, expected_out_hash);
+        assert_eq(outputs.out_hash, 0);
     }
 
     #[test]