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Secure Leaderboard Implementation

This document outlines the security measures preventing cheating in the Snake game leaderboard.

The Problem

The original contract allowed direct calls to submitScore(), enabling players to:

  • Submit fake scores without playing.
  • Use bots.
  • Manipulate scores via direct contract calls.

The Solution

We implemented a cryptographic signature system where scores must be signed by the game server before submission.

1. Cryptographic Signatures

The game server holds a private key. When a game finishes, the server signs the score along with the player's address and timestamp. The smart contract verifies this signature before accepting the score.

2. Replay Protection

  • Unique Signatures: Each signature is valid only once.
  • Expirations: Signatures expire after 5 minutes.

3. Game Data Validation

The API validates game data (duration, moves, score consistency) before signing to ensure the score was legitimately achieved.

Implementation Details

Workflow

  1. Player completes a game.
  2. Client sends move data to the API.
  3. API validates the data.
  4. If valid, API returns a signed score.
  5. Client submits the signed score to the smart contract.

Key Files

  • contracts/Leaderboard.sol: Signature verification logic.
  • app/api/sign-score/route.ts: Score signing endpoint.
  • lib/secure-score.ts: Signing utilities.

Deployment

  1. Generate a private key:

    node -e "console.log('0x' + require('crypto').randomBytes(32).toString('hex'))"

  2. Set GAME_SERVER_PRIVATE_KEY in .env.local.

  3. Deploy the contract:

    npx hardhat run scripts/deploy-secure-leaderboard.ts --network monad-testnet

Best Practices

  • Server: Keep the private key secure. Implement rate limiting and logging.
  • Client: Handle signature failures gracefully.

Testing Security

Attempting to submit fake scores, replay signatures, or bypass the server should fail with the current implementation.

Limitations

  • Server Dependence: Score submission requires the game server to be online.