SNARK Design, Part II, with Justin Thaler | a16z crypto research talks

TL;DR

Justin Thaler explains that rollups improve blockchain scalability by keeping a small cryptographic commitment, about 256 bits in his example, on layer one and pairing each updated commitment with a SNARK proof. He also outlines SNARK front ends, back ends, polynomial commitments, and the checks used to validate transaction batches, providing essential context for understanding practical SNARK and rollup design.

Transcript

um all right morning everyone welcome to today's a16z um crypto research seminar uh justin thaler from georgetown is back he's gonna be giving part two of his snarks tutorial we'll see if there's a part three later or not but for now let's let's hear part two thanks tim yes so um i'm going to start today by recapping the first uh talk in case um an... Read More

Key Insights

• 💨 SNARKs provide an efficient way to prove knowledge without revealing sensitive information, making them valuable for privacy and efficiency in blockchain systems.
• 🤣 Roll-up projects use commitments and SNARK proofs to store data more efficiently on the blockchain and increase scalability.
• 🤣 Front-end programming languages in roll-up projects range from SNARK-specific languages like Cairo to transpiled languages like Solidity, each with their own advantages and challenges.
• 🤣 Ensuring data availability is a critical aspect of roll-up projects, and various approaches, such as storing data on-chain or incentivizing external parties, are being explored.

Questions & Answers

Q: How do SNARKs help rollups verify blockchain transactions?

A rollup processes a batch of transactions, computes the resulting state, and posts a commitment to that new state on layer one. It pairs the commitment with a SNARK proving that the transactions are valid and that applying them to the old state produces the new committed state.

Q: What is a SNARK?

A SNARK lets a prover demonstrate knowledge of a witness satisfying a stated property with lower costs than simply sending the witness to the verifier. Its proof is shorter than the explicit witness and, ideally, faster for the verifier to check.

Q: What does a rollup store on layer one?

Instead of storing the entire state of the world on layer one, a rollup stores a cryptographic commitment to that data. Thaler describes this commitment as potentially being a single hash value of about 256 bits.

Q: Why does a rollup need a SNARK proof with its new state commitment?

Users should not have to trust that the rollup service applied every transaction correctly or computed the new commitment honestly. The SNARK proves that valid transactions transform the state behind the old commitment into the state behind the new one.

Q: What transaction conditions can a rollup's SNARK verify?

The proof can establish that the rollup knows a batch of valid transactions. Examples include checking that transactions have digital signatures and that nobody spends more money than is available in their account.

Q: What are the front end and back end of a SNARK system?

The front end converts a program written in a high-level language into an equivalent representation, typically something like a circuit satisfiability instance. The back end applies SNARK proof machinery to that circuit or to a practical variant or generalization of it.

Q: How is a SNARK designed in the standard three-step paradigm?

First, the designer creates a polynomial IOP, followed by a polynomial commitment scheme. Combining them produces a succinct interactive argument, and the Fiat-Shamir transformation removes the interaction to create a static, non-interactive proof.

Q: What example illustrates a prover's claim of knowledge in a SNARK?

The prover and verifier can agree on a cryptographic hash function and an output y. The prover claims to know a pre-image w whose hash is y, while the SNARK demonstrates that knowledge more efficiently than sending w directly.

Summary & Key Takeaways

• SNARKs, or succinct non-interactive arguments of knowledge, are used to prove that a prover has certain information without revealing it. They are designed to be more efficient than traditional proof systems.

• Roll-up projects aim to improve blockchain scalability by storing only commitments to data on the blockchain instead of the entire data itself. They use SNARK proofs to verify the correctness of the commitments and transactions.

• Front-end programming languages for roll-up projects include Cairo, which is designed specifically for SNARKs, and custom compilers for languages like Solidity. These languages require different levels of expertise and have varying trade-offs between expressiveness and efficiency.