Layer 2 Scaling Deep Dive — Rollups, Channels & Sidechains

// optimistic_rollup_sim.js
class OptimisticRollup {
    constructor(challengePeriodDays = 7) {
        this.state = { balances: {} };
        this.batches = [];
        this.challengePeriod = challengePeriodDays * 86400;
    }

    submitBatch(transactions, sequencer) {
        const batch = {
            id: this.batches.length + 1,
            transactions,
            sequencer,
            timestamp: Date.now(),
            challenged: false,
            finalized: false
        };
        this.batches.push(batch);
        console.log(`Batch #${batch.id} submitted by ${sequencer}`);
        console.log(`Contains ${transactions.length} transactions`);
        console.log(`Challenge period: ${this.challengePeriod / 86400} days`);
        return batch;
    }

    challengeBatch(batchId, challenger) {
        const batch = this.batches[batchId - 1];
        if (!batch || batch.finalized) return false;

        batch.challenged = true;
        console.log(`Batch #${batchId} challenged by ${challenger}!`);

        // In production, fraud proof verification happens here
        const fraudDetected = Math.random() > 0.9;

        if (fraudDetected) {
            console.log("FRAUD DETECTED! Sequencer penalized.");
            return true;
        }
        console.log("Challenge resolved — batch valid.");
        return false;
    }

    finalize(batchId) {
        const batch = this.batches[batchId - 1];
        if (!batch || batch.challenged) return;
        batch.finalized = true;
        console.log(`Batch #${batchId} finalized. Transactions irreversible.`);
    }
}

const rollup = new OptimisticRollup();
const batch = rollup.submitBatch(
    Array(100).fill({ from: "Alice", to: "Bob", amount: 1 }),
    "SequencerNode1"
);
rollup.challengeBatch(1, "ValidatorNode5");
rollup.finalize(1);

// Simplified ZK rollup verifier interface
contract ZKVerifier {
    address public verifierContract;

    // Verify a ZK proof that batch is valid
    function verifyBatch(
        bytes calldata proof,
        bytes32 newStateRoot,
        bytes32 oldStateRoot
    ) external returns (bool) {
        // Calls ZK proof verification contract
        (bool success, ) = verifierContract.call(
            abi.encodeWithSignature(
                "verify(bytes,bytes32,bytes32)",
                proof, newStateRoot, oldStateRoot
            )
        );
        require(success, "ZK proof verification failed");
        stateRoot = newStateRoot;
        emit BatchVerified(newStateRoot);
        return true;
    }

    event BatchVerified(bytes32 indexed stateRoot);
}

# sidechain_security_analyzer.py
def analyze_sidechain_security(name, validators, consensus, tvl):
    """
    Assess sidechain security compared to rollups.
    """
    eth_validators = 1_000_000  # Ethereum's validator count
    security_ratio = validators / eth_validators

    print(f"=== Sidechain Security: {name} ===")
    print(f"Validators: {validators:,}")
    print(f"Consensus: {consensus}")
    print(f"TVL: ${tvl}B")
    print(f"Validators vs Ethereum: {security_ratio:.4%}")

    if security_ratio < 0.01:
        print("Risk: VERY HIGH — small validator set")
        print("A 51% attack costs much less than on Ethereum")
    elif security_ratio < 0.1:
        print("Risk: MODERATE — larger set but still centralized")
    else:
        print("Risk: LOW — comparable to L1 security")

    print(f"\nIf {validators * 2 // 3:,} validators collude:")
    print("Funds can be stolen from the bridge")
    print("No recourse — sidechain has its own consensus")

analyze_sidechain_security("Polygon PoS", 100, "Proof of Stake", 6.8)