Arbitrum Nitro Deep Dive: WASM Fraud Proofs and Data Design

Frequently Asked Questions

01.What makes Arbitrum Nitro's fraud proofs WASM-based?

Arbitrum Nitro compiles its execution stack, including a full Geth core, down to WebAssembly, then runs disputed segments through WAVM, a WASM-compatible instruction set. This lets the interactive fraud proof bisect disagreements to a single WASM instruction and verify it on Ethereum with a one-step proof contract, without requiring a custom, hand-audited virtual machine like Arbitrum's pre-Nitro AVM.

02.How does Arbitrum's interactive fraud proof reach a one-step proof?

When a validator disputes an asserted state root, the two parties play a bisection game, repeatedly splitting the disputed execution range in half and posting hashes of intermediate states until only one WAVM instruction remains in disagreement. At that point, either party submits a one-step proof, a small piece of calldata that lets an Ethereum L1 contract execute that single instruction and determine which side lied.

03.What is Arbitrum's AnyTrust data availability design?

AnyTrust is the data availability mode used by Arbitrum Nova. Instead of posting full transaction data to Ethereum, the sequencer collects signatures from a Data Availability Committee under a 2-of-N honesty assumption and posts a compact certificate, called a DACert, to L1. If the committee cannot produce a valid certificate within minutes, the chain automatically falls back to posting full data on Ethereum, the same mode Arbitrum One uses.

04.How long is the Arbitrum Nitro challenge period?

Arbitrum Nitro's dispute window is approximately seven days (commonly cited as 6.4 days). An asserted state root only becomes final on Ethereum after this window closes without a successful challenge, which is why standard withdrawals from Arbitrum back to Ethereum take about a week unless a user pays a third-party liquidity provider for a fast exit.