ECDSA: Use unchecked arithmetic for the tryRecover function (#4301)

Signed-off-by: Pascal Marco Caversaccio <pascal.caversaccio@hotmail.ch>
OpenZeppelin · Jun 8, 2023 · 1d5bcd0 · 1d5bcd0
1 parent d947432
commit 1d5bcd0
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Showing 2 changed files with 11 additions and 3 deletions.
diff --git a/.changeset/four-adults-knock.md b/.changeset/four-adults-knock.md
@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': patch
+---
+
+`ECDSA`: Use unchecked arithmetic for the `tryRecover` function that receives the `r` and `vs` short-signature fields separately.
diff --git a/contracts/utils/cryptography/ECDSA.sol b/contracts/utils/cryptography/ECDSA.sol
@@ -98,9 +98,12 @@ library ECDSA {
      * _Available since v4.3._
      */
     function tryRecover(bytes32 hash, bytes32 r, bytes32 vs) internal pure returns (address, RecoverError) {
-        bytes32 s = vs & bytes32(0x7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff);
-        uint8 v = uint8((uint256(vs) >> 255) + 27);
-        return tryRecover(hash, v, r, s);
+        unchecked {
+            bytes32 s = vs & bytes32(0x7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff);
+            // We do not check for an overflow here since the shift operation results in 0 or 1.
+            uint8 v = uint8((uint256(vs) >> 255) + 27);
+            return tryRecover(hash, v, r, s);
+        }
     }
 
     /**