Crypto Newbie / Simulators / OR Fraud Proof
Optimistic Rollup Fraud Proof + Bridge Decision Simulator
Optimistic rollups assume their state is correct unless someone proves otherwise. The proof window: 7 days. This is why withdrawing from Arbitrum/Optimism/Base to Ethereum L1 takes a week via the native bridge. Fast 3rd-party bridges (Across, Hop, Orbiter) provide instant withdrawals for a fee. This simulator quotes both options, runs the fraud proof game mechanics (~25 bisection rounds × 24h each), and recommends which bridge to use based on your transfer amount.
Bridge from L2 to L1
Bridge quote
Total fee
$0.00
Fee as % of transfer: 0.000%
Estimated time
168 hrs
Bridge risk class: none
Native vs Fast bridge decision
Native fee
$0.00
Native time: 168 hrs
Cheapest fast bridge: orbiter
$25.00
Fast bridge time: 3 min
Extra cost per hour saved (going fast)
$0.1489/hr
Use native bridge (7-day delay is OK, save fees)
Interactive Fraud Proof Game
Bisection rounds needed
24
Gas cost per round
$31.50
Total gas cost (entire game)
$756.00
Bond locked during game
$10.50k
Total time (each round ~24h)
24.0 days
Winner's payoff (loser's bond)
+$10.50k
Why optimistic rollups exist and why 7 days
Ethereum L1 alone can do ~15 TPS. To scale, rollups process transactions OFF-CHAIN, then post just the STATE ROOT + transaction data back to L1. This compresses thousands of L2 txs into one L1 tx. Why 'optimistic'? Because L1 doesn't verify each L2 tx individually — it ASSUMES the posted state is correct, and only checks if challenged. The 7-day window is the time L1 waits for a fraud challenge. After 7 days with no challenge, the state is FINAL. Why 7 days specifically? Long enough that: (a) Honest validators can detect fraud even under DoS attacks. (b) The interactive bisection proof can complete (25 rounds × 24h each). (c) Network upgrades don't interrupt the protection.
Fast bridges — how they work and what they cost
Across, Hop, Orbiter, and others are 'fast bridges.' They observe your L2 withdrawal request, then immediately send you L1 funds from their own liquidity. They get reimbursed by the L2 protocol after the 7-day window expires. The fee they charge (0.05-0.30%) covers: (1) Their cost of capital (locked liquidity). (2) Their bridge security audits + smart contract risk. (3) Their gas costs. For most users, fast bridges are the right choice — you pay 0.05-0.30% to save 7 days. For very large transfers, native bridge can be worth it (no fee). For small transfers, the fixed component of fast bridge fees dominates.
Fraud proof game — interactive bisection protocol
If a validator detects fraud in a posted L2 state, they initiate the fraud proof game. Mechanic: asserter says state X is correct. Challenger disagrees. They bisect — asserter says intermediate state Y is correct, challenger disagrees. Bisect again. After log2(N) rounds where N = total L2 instructions in dispute, they narrow down to a SINGLE CPU instruction. L1 then executes that one instruction and determines who's right. For ~10M L2 instructions per block, this is ~24 rounds. Each round ~24 hours of game time (parties need to compute proofs). Total game time: 25-30 days for a major fraud. But: the 7-day challenge window starts the game; once started, the rest can take longer (and the L2 stays paused until resolved).
Why ZK rollups don't have this 7-day delay
ZK rollups (zkSync, Starknet, Scroll, Polygon zkEVM) post PROOFS that their state transition is correct. Verification is mathematical — L1 doesn't have to wait for a challenge window because the proof itself guarantees correctness. ZK rollup withdrawals: typically 0-1 hour. Trade-off: ZK proving is computationally intensive ($1000s+ per batch in 2023, dropping to $100s in 2024 with hardware advances). Optimistic rollups don't have this proving cost. So in practice: ZK = expensive proofs, fast withdrawals. Optimistic = cheap proofs, slow native withdrawals (fast 3rd-party bridges fill the UX gap). Both approaches dominate different segments of the market.
Frequently asked questions
+Has a fraud proof ever been triggered on a real optimistic rollup?
As of 2024, no successful fraud has been detected on Arbitrum, Optimism, or Base. The 7-day window has expired thousands of times without incident. This is partly good design (rollup code is well-audited), partly the small number of validators currently capable of submitting fraud proofs (most rollups have a few permissioned validators). True permissionless fraud proofs are being rolled out — Arbitrum BoLD (2024) opens fraud proofs to anyone. The mechanism works in theory; in practice, the security comes from the threat plus the existing honest-validator assumption.
+Are fast bridges safe?
Mostly yes, with caveats. Across is generally considered the safest — it uses UMA optimistic oracles for dispute resolution and has been battle-tested. Hop, Orbiter, others are also generally safe but have had occasional issues. The main risk: bridge smart contract bug or exploit, which could lock or lose user funds. Always check recent bridge security incidents before using. For large amounts ($100k+), some users prefer native bridge despite the 7-day wait — to avoid the bridge contract risk.
+What about Arbitrum One vs Arbitrum Nova vs Orbit chains?
Different products with different security models. Arbitrum One = main optimistic rollup, full L1 security, 7-day withdrawals. Arbitrum Nova = AnyTrust chain — uses a Data Availability Committee instead of posting all data to L1, much cheaper but slightly weaker security (depends on DAC trust). Withdrawals from Nova: still ~7 days through native bridge. Orbit chains = Arbitrum's framework for building custom L3s on top of Arbitrum One — these have their own security models depending on configuration. Always check before bridging.
+How do I check if the fraud proof window has expired?
On Arbitrum: go to bridge.arbitrum.io, view your withdrawal. It shows the L1 inclusion time and remaining wait period. On Optimism: app.optimism.io/bridge with same info. On Base: bridge.base.org. After 7 days expires, you click 'Claim' on L1 and pay an L1 gas fee to finalize the withdrawal. The native bridge will refund your full amount; fast bridges already pre-paid you. Always wait for full window to pass before claiming or you'll waste gas.
+Could there be an 'emergency withdrawal' if a rollup gets stuck?
All major optimistic rollups have FORCE INCLUSION mechanisms — if the rollup operator pauses or goes offline, users can still submit transactions through L1 contracts to force inclusion. This includes withdrawals. It's clunky (more expensive, multi-step) but ensures users can always exit. This 'escape hatch' is part of why rollups are considered safer than pure sidechains (Polygon PoS, BSC) — even if the operator is hostile, users can recover funds. The escape hatch has rarely been used (rollups have been reliable), but it's there as a backstop.