Cryptology ePrint Archive: Report 2021/1263

Transparency Dictionaries with Succinct Proofs of Correct Operation

Ioanna Tzialla and Abhiram Kothapalli and Bryan Parno and Srinath Setty

Abstract: This paper introduces Verdict, a transparency dictionary, where an untrusted service maintains a label-value map that clients can query and update (foundational infrastructure for end-to-end encryption and other applications). To prevent unauthorized modifications to the dictionary, for example, by a malicious or a compromised service provider, Verdict produces publicly-verifiable cryptographic proofs that it correctly executes both reads and authorized updates. A key advance over prior work is that Verdict produces efficiently-verifiable proofs while incurring modest proving overheads. Verdict accomplishes this by composing indexed Merkle trees (a new SNARK-friendly data structure) with Phalanx (a new SNARK that supports amortized constant-sized proofs and leverages particular workload characteristics to speed up the prover). Our experimental evaluation demonstrates that Verdict scales to dictionaries with millions of labels while imposing modest overheads on the service and clients.

Category / Keywords: cryptographic protocols / transparency, SNARKs, proofs, key-value stores

Date: received 21 Sep 2021, last revised 21 Sep 2021

Contact author: srinath at microsoft com, it608 at nyu edu, akothapa at andrew cmu edu, parno at cmu edu

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Version: 20210922:151023 (All versions of this report)

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