July 24, 2021

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SnarkPack: Practical SNARK Aggregation, by Nicolas Gailly and Mary Maller and Anca Nitulescu

Zero-knowledge SNARKs(zk-SNARKs) are non-interactive proof systems with short and efficiently verifiable proofs that do not reveal anything more than the correctness of the statement. zk-SNARKs are widely used in decentralised systems to address privacy and scalability concerns. One of the main applications is the blockchain, were SNARKs are used to prove computations with private inputs and reduce on-chain footprint verification and transaction sizes.

We design and implement SnarkPack, a new argument that further reduces the size of SNARK proofs by means of aggregation. Our goal is to provide an off-the-shelf solution that is practical in the following sense: (1) it is compatible with existing deployed systems, (2) it does not require any extra setup.

SnarkPack is designed to work with Groth16 scheme and has logarithmic size proofs and a verifier that runs in logarithmic time in the number of proofs to be aggregated. Most importantly, SnarkPack reuses the public parameters from Groth16 system, so it does not require a separate trusted setup ceremony.

The key tool for our construction is a new commitment scheme that uses as public parameters two existing Groth16 trusted setup ceremony transcripts. The commitment scheme allows us to instantiate a new optimised version of inner product pairing arguments without additional trusted setup.

SnarkPack can aggregate 8192 proofs in 8.7s and verify them in 33ms, including un-serialization time, yielding a verification mechanism that is exponentially faster than batching and previous solutions in the field.