Author: Chloe
The current expansion solution based on zero-knowledge proof of Ethereum is ZK-rollup, but there are actually two other solutions-Validium and Volitions.
This article briefly introduces the above three expansion schemes based on zero-knowledge proofs.
ZK rollup
The operation of ZK-rollup is simply to package multiple transactions together and publish them on L1, and at the same time issue a proof (using zero-knowledge proof technology) to claim that these transactions are valid. Once verified on L1, then zk- The status of the rollup is updated.
This set of proof mechanism is also called "validity proof". At present, the main proof mechanisms used by ZK-rollup are zkSNARK and zkSTARK.
In particular, zk-SNARK is the most widely used, and zk-SNARK is an improved version of it, and there are not many users currently.
zk-SNARK stands for zero-knowledge succinct non-interactive argument on knowledge (concise non-interactive zero-knowledge proof), which is an encrypted proof with small files and easy verification, and the simplicity lies in non-interactive.
The traditional scheme is interactive proof, that is, repeated confirmation between the prover and the verifier. You can understand that the demonstrator keeps asking the verifier "yes or no?", and the verifier keeps giving answers until finally a correct answer is found, so the efficiency is very low.
The SNARK solution is to do a "trusted initialization" in advance to generate a public reference string (CRS), so that all demonstrators can directly access it. You can understand that there is a standard answer, and the demonstrator verifies it like correcting a test paper.
However, SNARK generates public reference strings in advance to improve efficiency, but it also leaves hidden dangers - what if the public reference strings are leaked? So STARK was born.
STARK is an interactive proof, but it is a clever interactive proof - the security is guaranteed by hash function collision (a way of probabilistic proof), so it is also more efficient (but still not as efficient as SNARK).
Validiums
ZK-rollup is to send transactions to L1 in batches for execution. It is a kind of "custom security" that does not require trust.
Validiums are executed directly off-chain, and maintain data through zero-knowledge proofs, and verify the validity of withdrawal requests on the main network only when needed.
Therefore, the scalability of Validiums is higher than that of ZK-rollup (currently the highest TPS can reach more than 20,000), but it is a "weak trust expansion" that transfers trust to a third party outside the chain. It will be attacked and cause data unavailable or users cannot Withdraw funds.
The way to solve security is to adopt the PoS mechanism and use economic incentives to ensure that data is stored in each node and is available at any time.
The representative project currently adopting the Validiums solution is Immutable X, an expansion solution centered on NFT.
Vitalik believes that Validiums is actually seriously underestimated, because most Dapps can already meet their operational requirements with Validiums.
Volitions
Combining ZK-rollup and validium, the StarkWare team creatively launched the Volitions solution, which, as the name suggests, is about "decision-making ability".
The Volitions solution essentially provides ZK-rollup and validium services at the same time. They share the same state root (state root), and users can choose the DA mode of each transaction by themselves. Even if the Validium part is compromised, the funds on the ZK-rollup are still safe.
epilogue
epilogue
The Ethereum expansion war is still just beginning. Currently, the Optimistic rollups camp has the upper hand. They can be EVM compatible or even completely equivalent. In addition, the community operation capability is also very strong.
ZK-rollup's downfall is largely due to the need to customize the VM from the start, which means that the code from the EVM has to be written from scratch (although it has become less and less difficult).
However, in the long run, compared to Optimistic rollups, ZK rollups have built-in privacy and security advantages, and the future EVM compatibility is likely to outperform Optimistic rollups.
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