Description:
The commitMove mechanism relies on keccak256(abi.encodePacked(move, salt)) to conceal a player's move until the reveal phase. However, the contract does not enforce or validate that the salt is unique per game or per turn. If a player reuses a salt that was revealed in a previous game, an attacker can reconstruct the commit off-chain and predict the move before the reveal.

Impact:

• A malicious opponent can detect repeated commit hashes by comparing them with previous publicly revealed moves and salts.

• This breaks the secrecy and fairness of the commit-reveal scheme.

• Allows front-running and unfair strategic advantage to a player who monitors the chain.

Proof of Concept:

➡️ This demonstrates that any previously revealed salt and move combination can be used to predict future plays if reused.

Output (-vvvv)

forge test --mt test_ReusedSaltCanBePredicted -vvvv

Recommended Mitigation:

• Enforce that each commit is unique per game and per turn using a mapping(bytes32 => bool) usedCommits.

• Reject reused commit hashes:

• Recommend salts with high entropy (e.g., keccak256(abi.encodePacked(msg.sender, block.timestamp, nonce))) on the frontend.

This ensures that even if a player accidentally reuses their salt, the contract logic prevents it and preserves fairness.