International Association for Cryptologic Research

International Association
for Cryptologic Research


Non-Malleable Time-Lock Puzzles and Applications

Cody Freitag
Ilan Komargodski
Rafael Pass
Naomi Sirkin
DOI: 10.1007/978-3-030-90456-2_15
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Abstract: Time-lock puzzles are a mechanism for sending messages "to the future", by allowing a sender to quickly generate a puzzle with an underlying message that remains hidden until a receiver spends a moderately large amount of time solving it. We introduce and construct a variant of a time-lock puzzle which is non-malleable, which roughly guarantees that it is impossible to "maul" a puzzle into one for a related message without solving it. Using non-malleable time-lock puzzles, we achieve the following applications: - The first fair non-interactive multi-party protocols for coin flipping and auctions in the plain model without setup. - Practically efficient fair multi-party protocols for coin flipping and auctions proven secure in the (auxiliary-input) random oracle model. As a key step towards proving the security of our protocols, we introduce the notion of functional non-malleability, which protects against tampering attacks that affect a specific function of the related messages. To support an unbounded number of participants in our protocols, our time-lock puzzles satisfy functional non-malleability in the fully concurrent setting. We additionally show that standard (non-functional) non-malleability is impossible to achieve in the concurrent setting (even in the random oracle model).
Video from TCC 2021
  title={Non-Malleable Time-Lock Puzzles and Applications},
  booktitle={Theory of Cryptography;19th International Conference},
  author={Cody Freitag and Ilan Komargodski and Rafael Pass and Naomi Sirkin},