Non-interactive Cryptographic Timestamping based on Verifiable Delay Functions.

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Presented at FinancialCryptographyandDataSecurity 2020 by

Marc Stevens

Christian Schaffner

Esteban Landerreche

We present the first treatment of non-interactive publiclyverifiable timestamping schemes in the Universal Composability framework. Inspired by the timestamping properties of Bitcoin, we use nonparallelizable computational work that relates to elapsed time to avoidprevious impossibility results on non-interactive timestamping. We introduce models of verifiable delay functions (VDF) related to a clockand non-interactive timestamping in the UC-framework. These are usedto present a secure construction that provides improvements over previous concrete constructions. Namely, timestamps forged by the adversaryare now limited to a certain time-window that depends only on the adversary’s ability to compute VDFs more quickly and on the length ofcorruption. Finally, we discuss how our construction can be added tonon-PoW blockchain protocols to prevent costless simulation attacks.