Cryptology ePrint Archive: Report 2020/504

Storing and Retrieving Secrets on a Blockchain

Vipul Goyal and Abhiram Kothapalli and Elisaweta Masserova and Bryan Parno and Yifan Song

Abstract: Multiple protocols implementing exciting cryptographic functionalities using blockchains such as time-lock encryption, one-time programs and fair multi-party computation assume the existence of a cryptographic primitive called extractable witness encryption. Unfortunately, there are no known efficient constructions (or even constructions based on any well studied assumptions) of extractable witness encryption. In this work, we propose a protocol that uses a blockchain itself to provide a functionality that is effectively the same as extractable witness encryption. By making small adjustments to the blockchain code, it is possible to easily implement applications that rely on extractable witness encryption and existed only as theoretical designs until now. There is also potential for new applications. As a key building block, our protocol uses a new and highly efficient batched dynamic proactive secret sharing scheme which may be of independent interest. We provide a proof-of-concept implementation of the extractable witness encryption construction and the underlying dynamic proactive secret sharing protocol.

Category / Keywords: applications / Blockchain, Extractable Witness Encryption, Dynamic Proactive Secret Sharing

Date: received 29 Apr 2020, last revised 18 Jun 2020

Contact author: goyal at cs cmu edu,elisawem@cs cmu edu,parno@cmu edu,yifans2@andrew cmu edu,akothapa@andrew cmu edu

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Version: 20200618:155944 (All versions of this report)

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