refactor(sol): use Hash.sha256ToField library where required (#637)

* refactor(sol): use Hash.sha256ToField library where required * fmt :) * feat: expose bytes32 hash directly * fmt: https://i.pinimg.com/originals/81/23/a1/8123a132c007eab782d6ca9bed517eb3.jpg --------- Co-authored-by: Maddiaa0 <[email protected]>
AztecProtocol · May 22, 2023 · 9d3ea2c · 9d3ea2c
1 parent a613419
commit 9d3ea2c
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diff --git a/l1-contracts/src/core/Decoder.sol b/l1-contracts/src/core/Decoder.sol
@@ -2,6 +2,8 @@
 // Copyright 2023 Aztec Labs.
 pragma solidity >=0.8.18;
 
+import {Hash} from "@aztec/core/libraries/Hash.sol";
+
 /**
  * @title Decoder
  * @author Aztec Labs
@@ -108,10 +110,6 @@ contract Decoder {
   uint256 internal constant CONTRACTS_PER_KERNEL = 1;
   uint256 internal constant L1_TO_L2_MSGS_PER_ROLLUP = 16;
 
-  // Prime field order
-  uint256 internal constant P =
-    21888242871839275222246405745257275088548364400416034343698204186575808495617;
-
   /**
    * @notice Decodes the inputs and computes values to check state against
    * @param _l2Block - The L2 block calldata.
@@ -167,7 +165,7 @@ contract Decoder {
       mstore(add(temp, add(0x20, endOfTreesData)), _diffRoot)
       mstore(add(temp, add(0x40, endOfTreesData)), _l1ToL2MsgsHash)
     }
-    return bytes32(uint256(sha256(temp)) % P);
+    return Hash.sha256ToField(temp);
   }
 
   /**
@@ -504,7 +502,7 @@ contract Decoder {
 
       // Compute current iteration's logs hash and truncate the hash to field
       // See: https://discourse.aztec.network/t/proposal-forcing-the-sequencer-to-actually-submit-data-to-l1/426/2
-      logsHash = bytes32(uint256(sha256(temp)) % P);
+      logsHash = Hash.sha256ToField(temp);
     }
 
     return (logsHash, offset);

diff --git a/l1-contracts/src/core/libraries/Hash.sol b/l1-contracts/src/core/libraries/Hash.sol
@@ -47,4 +47,14 @@ library Hash {
   function sha256ToField(bytes memory _data) internal pure returns (bytes32) {
     return bytes32(uint256(sha256(_data)) % Constants.P);
   }
+
+  /**
+   * @notice Computes the sha256 hash of the provided data and converts it to a field element
+   * @dev Using modulo to convert the hash to a field element.
+   * @param _data - A bytes32 value to hash
+   * @return The hash of the provided data as a field element
+   */
+  function sha256ToField(bytes32 _data) internal pure returns (bytes32) {
+    return sha256ToField(abi.encodePacked(_data));
+  }
 }
diff --git a/l1-contracts/test/Decoder.t.sol b/l1-contracts/test/Decoder.t.sol
@@ -5,7 +5,7 @@ pragma solidity >=0.8.18;
 import {Test} from "forge-std/Test.sol";
 
 import {Decoder} from "@aztec/core/Decoder.sol";
-import {Constants} from "@aztec/core/libraries/Constants.sol";
+import {Hash} from "@aztec/core/libraries/Hash.sol";
 import {DecoderHelper} from "./DecoderHelper.sol";
 
 /**
@@ -144,12 +144,9 @@ contract DecoderTest is Test {
 
     // Note: First 32 bytes are 0 because those correspond to the hash of previous iteration and there was no previous
     //       iteration.
-    bytes32 referenceLogsHash = bytes32(
-      uint256(
-        sha256(
-          hex"0000000000000000000000000000000000000000000000000000000000000000aafdc7aa93e78a70"
-        )
-      ) % Constants.P
+
+    bytes32 referenceLogsHash = Hash.sha256ToField(
+      hex"0000000000000000000000000000000000000000000000000000000000000000aafdc7aa93e78a70"
     );
 
     assertEq(bytesAdvanced, emptyKernelData.length, "Advanced by an incorrect number of bytes");
@@ -167,22 +164,12 @@ contract DecoderTest is Test {
       hex"0000002400000008aafdc7aa93e78a700000001497aee30906a86173c86c6d3f108eefc36e7fb014";
     (bytes32 logsHash, uint256 bytesAdvanced) = helper.computeKernelLogsHash(emptyKernelData);
 
-    bytes32 referenceLogsHashFromIteration1 = bytes32(
-      uint256(
-        sha256(
-          hex"0000000000000000000000000000000000000000000000000000000000000000aafdc7aa93e78a70"
-        )
-      ) % Constants.P
+    bytes32 referenceLogsHashFromIteration1 = Hash.sha256ToField(
+      hex"0000000000000000000000000000000000000000000000000000000000000000aafdc7aa93e78a70"
     );
 
-    bytes32 referenceLogsHashFromIteration2 = bytes32(
-      uint256(
-        sha256(
-          bytes.concat(
-            referenceLogsHashFromIteration1, hex"97aee30906a86173c86c6d3f108eefc36e7fb014"
-          )
-        )
-      ) % Constants.P
+    bytes32 referenceLogsHashFromIteration2 = Hash.sha256ToField(
+      bytes.concat(referenceLogsHashFromIteration1, hex"97aee30906a86173c86c6d3f108eefc36e7fb014")
     );
 
     assertEq(bytesAdvanced, emptyKernelData.length, "Advanced by an incorrect number of bytes");