SuperEx Educational Series: Understanding ZK Rollup

#ZKRollup #EducationalSeries

Today, we continue our deep dive into the Rollup family. This session focuses on ZK Rollup. As a Layer 2 scaling solution, it cleverly leverages zero-knowledge proof technology to ensure the correctness of off-chain computation, achieving high throughput while still maintaining the same level of security as the main chain.

Put simply, within the Rollup world, Optimistic Rollup is more like an engineering approach of “assume honesty first, then correct errors afterward”; ZK Rollup, on the other hand, chose a completely different path from the very beginning.

It does not ask: “If you misbehave, can I detect it?”
It asks instead: “Can you mathematically prove that you did not misbehave?”

These two ways of thinking determine their fundamental differences in security models, performance boundaries, and engineering complexity.

https://news.superex.com/articles/30134.html

What ZK Rollup Wants to Solve Is Not “Whether to Trust,” but “Whether Trust Is Needed at All”

In Optimistic Rollup, Layer 1 can trust the results of Layer 2 because:as long as someone finds a problem → an incorrect state can be overturned through a Fraud Proof.

At its core, this is still built on a prerequisite:there must be at least one honest watcher online.

ZK Rollup directly bypasses this prerequisite. Its core logic is:every state update must be accompanied by a “proof of correctness.”

This proof is not “I promise I am correct,” but rather:without re-executing the transactions, it mathematically proves that this batch of computation must be correct. As long as the proof holds, Layer 1 no longer needs to care how the computation was performed, who performed it, or whether anyone was watching.

This means:

No reliance on a challenge period
No reliance on active watchers
No window where “misbehavior succeeds simply because no one challenges”

Security is pushed directly to the submission stage. And the significance of this “front-loaded security” is far more than a process optimization — it is a complete rewrite of the trust cost structure.

In Optimistic Rollup, what the system truly trusts is not the Sequencer itself, but a more implicit assumption:
that there will always be enough motivated, capable, and continuously online watchers in the network.

This assumption is not always solid in reality, because monitoring has real costs:

Running nodes continuously
Staying fully synchronized with state
Understanding complex execution logic

And acting quickly within a limited challenge window. Once the number of watchers declines, or monitoring incentives weaken, system security does not collapse immediately — but an attack “window” genuinely exists.

The design of ZK Rollup is intentionally aimed at bypassing this hidden risk. It does not require anyone to “watch the system,” nor does it assume that “bad behavior will always be discovered in time.” Instead, it rewrites the problem as:if you want to submit an incorrect state, can you mathematically forge a valid proof?

The answer is: almost impossible.

Because the security of zero-knowledge proofs does not rely on behavioral assumptions, but on:

Clearly defined cryptographic hardness assumptions
Formally verifiable constraint systems
Repeatable, tamper-proof mathematical conclusions

This shifts the attacker’s challenge away from “will anyone catch me?” to:do I have the ability to break a known computationally infeasible boundary?

From a game-theoretic perspective, this is a crucial change.

In Optimistic Rollup, attacks are probabilistic events:

Betting that no one challenges
Betting that challenges are not timely
Betting that execution complexity is high enough

In ZK Rollup, attacks resemble physically impossible events:

Either the proof is valid
Or the state is outright invalid
There is no gray zone

This also explains why many people say that ZK Rollup is not “more decentralized,” but rather less dependent on social consensus and behavioral incentives. It compresses security — previously maintained through participant games — into a single deterministic verification step.

In other words:

Optimistic Rollup is an “after-the-fact correction system”
ZK Rollup is a “pre-constraint system”

The former relies on time and participants; the latter relies on mathematics and structure. And this is precisely the most fundamental — and most easily underestimated — value of ZK Rollup’s trust model.

What Exactly Do Zero-Knowledge Proofs Prove in Rollups?

When people first hear about ZK Rollups, they are often misled by the term “zero knowledge.” In the Rollup context, “zero knowledge” is not the core point — the proof is.

The proof generated by a ZK Rollup essentially proves three things:

The transactions are valid (correct signatures, sufficient balances)
The execution logic is correct (state transitions follow the rules)
The new state is indeed derived from the old state plus this batch of transactions

The key point is: these proofs can be quickly verified by Layer 1, but are almost impossible to forge. Verification is cheap, while forgery is extremely expensive. This creates a very typical structure: Layer 2 bears the heavy computation and proof generation costs, while Layer 1 only performs lightweight verification and final arbitration.

The result is that computation is fully “outsourced,” yet security is not diluted.

Why ZK Rollup Does Not Have a Challenge Period

Optimistic Rollup requires a challenge period because it submits only the “result,” not the “proof of the result.” Time must therefore be given for others to check it.

ZK Rollup’s state update logic is:

Batch transactions
Compute the new state
Generate a validity proof simultaneously
Submit everything together to Layer 1

When Layer 1 receives it, it does only one thing: verify whether the proof is valid.

If the proof is invalid, the state is immediately rejected
If the proof is valid, the state takes effect immediately

This leads to a very intuitive outcome:

No need to wait for a challenge period
Faster withdrawals
Stronger state finality

This is why many people say ZK Rollup is closer to a Layer 2 with “instant finality.”

The Hard Part of ZK Rollup Is Not On-Chain, but Off-Chain

If you only look at the runtime results, ZK Rollup almost appears to be a “perfect solution.” But in reality, its engineering difficulty is mainly concentrated in the off-chain system.

1. Proof generation is extremely complex

Generating a ZK proof means translating transaction logic into provable circuits. These proofs are executed under constrained computation models and incur significantly higher costs than ordinary execution. This is why ZK Rollup infrastructure typically requires much longer development cycles.

2. Extremely unfriendly to developers (at least in the past)

Early ZK Rollups faced problems such as:

Smart contracts not compatible with EVM
Difficult debugging
High costs and immature toolchains

This is also why Optimistic Rollups initially advanced faster. However, this gap is now shrinking rapidly.

The Evolution of ZK Rollup: From “It Works” to “It’s Usable”

Over the past two years, the focus of ZK Rollup development has become very clear: it is no longer about proving that it is “secure,” but about making it “as usable as Ethereum.”

This includes, but is not limited to:

zkEVM: compatibility with EVM semantics
Faster proof generation
Lower off-chain computation costs
More developer-friendly tooling

This has gradually clarified ZK Rollup’s positioning: it is no longer just a “technical flex,” but is striving to become a truly scalable execution layer.

Optimistic vs ZK: Not About Right or Wrong, but About Stage Choice

Many discussions like to ask: “Will only ZK Rollups remain in the end?” But from an engineering perspective, this question itself is not very meaningful.

The core difference between the two is:

Optimistic Rollup: trades time for simplicity, error correction for usability
ZK Rollup: trades complexity for determinism, mathematics for trust

At different stages and under different resource constraints, both paths are reasonable. What truly matters is not “which one wins,” but the fact that Rollups have fundamentally changed the question of who computes and who must be trusted.

Final Thoughts

The significance of ZK Rollup lies not only in being “faster” or “more secure.” What it truly changes is a long-standing assumption: that blockchains must re-execute computation in order to establish trust.

ZK Rollup’s answer is: re-execution is not necessary — proof is enough.

When computation and verification are fully decoupled, the way blockchains scale is no longer constrained by node computation limits. And this may well be the most important aspect of ZK Rollup to truly understand.