A Fraud Proof or Fault Proof is the standard security assurance mechanism employed by Optimistic rollups. Fault proofs are submitted and processed retroactively when an observer detects and reports fraud for a financial incentive. Fault Proof schemes fall under non-interactive and interactive types; the former is architecturally the simpler of the two. Still, it is computationally expensive as the proof is fully validated on-chain, and the latter is more complex architecturally but has more minor validation requirements. In comparison to validity proofs, fraud proofs are computationally light and are only processed when submitted.