Bitcoin Rollups: Security Model in Practice

A rollup that only posts data to Bitcoin but uses a multi-sig for state validation is a sovereign chain with a Bitcoin data feed. Its security is defined by the honesty of its ~$1B+ staked validator set, not Bitcoin's PoW. This is the dominant model (e.g., early Stacks, many sidechains).\n- Security Ceiling: Capped at the economic security of the validator bond.\n- Trust Assumption: Users must trust a new, smaller set of actors.\n- Reality: This is a bridge security model, not a rollup security model.

BitVM enables optimistic rollups by expressing fraud-proof logic in Bitcoin Script. A single honest verifier can challenge invalid state transitions, forcing a Bitcoin L1 dispute resolution. This moves the security from a validator set to Bitcoin's consensus.\n- Security Floor: One honest participant is sufficient for safety.\n- Cost: Fraud proofs are expensive (~$10k+ in fees) but only paid in case of fraud.\n- Status: Theoretical, with prototypes from Botanix Labs and Citrea; mainnet is the ultimate test.

Rollups like Elastos' BeL2 and B² Network use zk-proofs for validity and Bitcoin for data availability (DA). Security is a hybrid: Validity is guaranteed by cryptography, but liveness depends on sequencers posting data. Censorship resistance inherits from Bitcoin if data is forced via covenants.\n- Key Benefit: No need for active fraud proofs; state is always correct.\n- Weakness: If sequencers censor, the chain halts, requiring social consensus.\n- Throughput: ~2000 TPS possible, limited by Bitcoin block space for data.

Models like RGB and client-side validation (CSV) treat Bitcoin purely as a timestamping service. Users directly verify the entire history of their assets. This provides maximal censorship resistance and aligns with Bitcoin's peer-to-peer ethos, but at a massive UX cost.\n- Security Model: User-operated; security scales with user vigilance.\n- Adoption Friction: Requires users to store and validate all relevant data.\n- Niche: Ideal for high-value, non-interactive assets like digital gold or securities.

Bitcoin's ~1MB block size and ~10-minute block time create a severe data bandwidth constraint. Rollups must compete for this scarce resource, making high-throughput systems economically unviable without layer-2 data solutions.\n- Hard Cap: ~4MB of rollup data per hour at base layer.\n- Cost Driver: Data posting fees will become the primary cost, not computation.\n- Innovation Required: Solutions like BitVM's tapleaf trees or off-chain DA with checkpointing are essential.

The practical security of a Bitcoin rollup today is inversely proportional to the size of its active validator set. A system with 5 signers is a federated bridge. One with 10,000 light clients is meaningfully decentralized. The trajectory from multi-sig to BitVM/zk-proofs + decentralized sequencing is the only path to true Bitcoin security inheritance.\n- Red Flag: A small, permissioned set of entities controlling state updates.\n- Green Flag: A mechanism that allows any user to force correct execution via Bitcoin L1.

Your security model dictates your governance. Sovereign rollups (e.g., early BitVM designs) rely on a multi-signature federation for data posting and fraud proofs, trading some decentralization for flexibility. Enshrined rollups (a future goal) would have validation logic directly in a Bitcoin soft fork, achieving maximal security but requiring years of consensus.

• Key Benefit 1: Sovereign models enable faster iteration and custom VMs today.
• Key Benefit 2: Enshrined path offers the ultimate credibly neutral security, aligning with Bitcoin's ethos.

Execution is cheap to verify; data hiding is the primary attack. Most practical security boils down to how and where you post transaction data. Taproot commitments and Bitcoin inscriptions are the current primitive, but they're expensive and limited to ~4MB per block.

• Key Benefit 1: Using Bitcoin L1 for DA provides cryptographic certainty of data existence.
• Key Benefit 2: Emerging layers like Nakachain or Citrea aim to provide scalable, Bitcoin-backed DA at lower cost.

Unlike optimistic rollups on Ethereum, Bitcoin has no smart contract to automatically slash a bond. BitVM-style fraud proofs are a challenge-response game played off-chain, requiring at least one honest participant to be watching and challenging invalid state transitions.

• Key Benefit 1: Creates a 1-of-N honest actor security assumption, which is pragmatic.
• Key Benefit 2: Shifts the security cost from capital lock-up (bonds) to operational vigilance.

The mechanism to move assets between L1 and L2 is your system's most critical trust point. A multi-signature federation is the current standard (see Stacks, Liquid), but it introduces a custodial risk. The endgame is a non-custodial bridge enabled by BitVM2 or similar, which allows users to unilaterally withdraw.

• Key Benefit 1: Multi-sig bridges are battle-tested and can be secure with reputable signers.
• Key Benefit 2: Non-custodial designs eliminate intermediate trust, matching Bitcoin's self-custody model.