MultiversX Constant Time Analysis

This skill helps you verify that cryptographic secrets are handled in constant time to prevent timing attacks.

1. When to Use

• Custom Crypto: If the contract implements Elliptic Curve math, ZK verification, or signatures manually (not using the API).
• Comparison: Checking secrets (e.g., comparing user-provided HASH against stored HASH).

2. Patterns to Avoid (Variable Time)

• Early Exit: if byte[i] != other[i] { return false }. This leaks the index of the first difference.
• Short-circuiting: && or || on secrets.

3. MultiversX Solution

• Managed Types: Use ManagedBuffer comparison provided by the API (often constant time implementation in the VM).
• Subtle crate: Use subtle::ConstantTimeEq for manual u8 slice comparisons.

4. Verification

• Measurement: Difficult on-chain due to Gas Metering. Gas usually leaks the execution trace roughly.
• Rule: Rely on the VM's crypto functions (self.crypto().verify_signature(...)) instead of implementing it in WASM.