COSIC seminar – Overview on Zcash and an Efficient zk-SNARK with Non-malleable Proofs – Shahla Atapoor (University of Tartu) Among various zero-knowledge proof systems, zk-SNARKs are the most efficient ones that are deployed in various applications of blockchains to achieve anonymity. Currently, Groth’s zk-SNARK from Eurocrypt 2016 is the most efficient one that is constructed for Quadratic Arithmetic Programs (QAPs), but its proof is vulnerable to the malleability attacks. In Crypto 2017, Groth and Maller proposed the first Square Arithmetic Program (SAP) based zk-SNARK that generates non-malleable proofs, but it is inefficient in comparison with Groth’s zk-SNARK.
In the first part of this presentation, we will give a short overview of the construction of Zcash and the way that it uses zk-SANRKs to generate anonymous transactions. In the second part, we will present a variation of Groth’s zk-SNARK and show that it guarantees non-malleability of proofs and outperforms Groth and Maller’s scheme in practical cases. The proposed variation is achieved by applying some changes in the underlying language using an OR contraction. Analysis that in practical cases overload has minimal effects on the efficiency of the original scheme.
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