Welcome to the resource topic for 2024/769
Title:
Time-Based Cryptography From Weaker Assumptions: Randomness Beacons, Delay Functions and More
Authors: Damiano Abram, Lawrence Roy, Mark Simkin
Abstract:The assumption that certain computations inherently require some sequential time has established itself as a powerful tool for cryptography. It allows for security and liveness guarantees in distributed protocols that are impossible to achieve with classical hardness assumptions. Unfortunately, many constructions from the realm of time-based cryptography are based on new and poorly understood hardness assumptions, which tend not to stand the test of time (cf. Leurent et al. 2023, Peikert & Tang 2023).
In this work, we make progress on several fronts. We formally define the concept of a delay function and present a construction thereof from minimal assumptions. We show that these functions, in combination with classical cryptographic objects that satisfy certain efficiency criteria, would allow for constructing delay encryption, which is otherwise only known to exist based on a new hardness assumption about isogenies. We formally define randomness beacons as they are used in the context of blockchains, and we show that (linearly homomorphic) time-lock puzzles allow for efficiently constructing them. Finally, we resolve an open question of Malavolta and Thyagarajan by constructing fully homomorphic time- lock puzzles from linearly homomorphic time-lock puzzles and multi-key fully homomorphic encryption, whereas their previous construction required indistinguishability obfuscation.
Our work puts time-based cryptography on a firmer theoretical footing, provides new constructions from simpler assumptions, and opens new avenues for constructing delay encryption.
ePrint: https://eprint.iacr.org/2024/769
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