feat: have difficulty always return zero

integration-tests/contracts/OVMContextStorage.sol

@@ -5,11 +5,13 @@ pragma solidity >=0.7.0;
 contract OVMContextStorage {
     mapping (uint256 => uint256) public blockNumbers;
     mapping (uint256 => uint256) public timestamps;
+    mapping (uint256 => uint256) public difficulty;
     uint256 public index = 0;
 
     fallback() external {
         blockNumbers[index] = block.number;
         timestamps[index] = block.timestamp;
+        difficulty[index] = block.difficulty;
         index++;
     }
 }

integration-tests/test/ovmcontext.spec.ts

@@ -72,6 +72,10 @@ describe('OVM Context: Layer 2 EVM Context', () => {
       expect(receipt.blockNumber).to.deep.equal(blockNumber.toNumber())
       const timestamp = await OVMContextStorage.timestamps(i)
       expect(block.timestamp).to.deep.equal(timestamp.toNumber())
+
+      // Difficulty should always be zero.
+      const difficulty = await OVMContextStorage.difficulty(i)
+      expect(difficulty.toNumber()).to.equal(0)
     }
   }).timeout(150000) // this specific test takes a while because it involves L1 to L2 txs
 

l2geth/core/evm.go

@@ -68,7 +68,7 @@ func NewEVMContext(msg Message, header *types.Header, chain ChainContext, author
 			Coinbase:        beneficiary,
 			BlockNumber:     msg.L1BlockNumber(),
 			Time:            new(big.Int).SetUint64(msg.L1Timestamp()),
-			Difficulty:      new(big.Int).Set(header.Difficulty),
+			Difficulty:      new(big.Int), // Difficulty always returns zero.
 			GasLimit:        header.GasLimit,
 			GasPrice:        new(big.Int).Set(msg.GasPrice()),
 			L1MessageSender: l1MessageSender,