🔒 Secure Meta-Transaction Replay Protection

[mijinummi]

📌 Overview

Meta-transactions enable users to submit gasless transactions via relayers. However, without proper safeguards, these transactions are vulnerable to replay attacks, where a malicious actor resubmits a transaction to drain funds or manipulate state.

This task introduces Secure Meta-Transaction Replay Protection to harden the gasless transaction flow by enforcing nonce validation and signature expiration.

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🎯 Objective

Build a protection system that:

• Validates nonces for each meta-transaction
• Enforces signature expiration to prevent replay over time
• Ensures secure and deterministic processing of gasless transactions
• Maintains backward compatibility with existing relayer infrastructure

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🛠 Scope of Work

1️⃣ Nonce Validation

• Maintain a per-user nonce tracking system
• Ensure incoming meta-transactions use the next expected nonce
• Reject duplicate or out-of-order transactions

Example behavior:

User	Expected Nonce	Received Nonce	Result
0x123...	10	10	Accepted
0x123...	10	9	Rejected (replay)
0x123...	10	10	Rejected (duplicate)

• Store nonces in:
  • On-chain mapping (recommended for decentralization)
  • Off-chain cache (Redis) for fast validation

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2️⃣ Signature Expiration

• Include expiry field in meta-transaction payload
• Reject transactions after expiration timestamp
• Provide clear rejection response:

{
  "error": "SignatureExpired",
  "message": "Meta-transaction signature has expired."
}