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Homomorphic Time-Lock Puzzles and Applications

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Advances in Cryptology – CRYPTO 2019 (CRYPTO 2019)

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Abstract

Time-lock puzzles allow one to encrypt messages for the future, by efficiently generating a puzzle with a solution s that remains hidden until time \(\mathcal {T}\) has elapsed. The solution is required to be concealed from the eyes of any algorithm running in (parallel) time less than \(\mathcal {T}\). We put forth the concept of homomorphic time-lock puzzles, where one can evaluate functions over puzzles without solving them, i.e., one can manipulate a set of puzzles with solutions \((s_1, \dots , s_n)\) to obtain a puzzle that solves to \(f(s_1, \ldots , s_n)\), for any function f. We propose candidate constructions under concrete cryptographic assumptions for different classes of functions. Then we show how homomorphic time-lock puzzles overcome the limitations of classical time-lock puzzles by proposing new protocols for applications of interest, such as e-voting, multi-party coin flipping, and fair contract signing.

G. Malavolta—Part of the work done while at Friedrich-Alexander-Universität Erlangen-Nürnberg.

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Notes

  1. 1.

    We implicitly assume that all puzzles are honestly generated, which can be enforced with standard cryptographic tools.

  2. 2.

    In [20] the signing algorithm requires an additional timing parameter, which we fix to be the round number and omit for the sake of clarity.

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Acknowledgements

Research supported in part by a gift from Ripple, a gift from DoS Networks, a grant from Northrop Grumman, a Cylab seed funding award, and a JP Morgan Faculty Fellowship.

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Authors and Affiliations

  1. Carnegie Mellon University, Pittsburgh, USA

    Giulio Malavolta

  2. Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany

    Sri Aravinda Krishnan Thyagarajan

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  1. Giulio Malavolta
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Correspondence to Giulio Malavolta or Sri Aravinda Krishnan Thyagarajan .

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Editors and Affiliations

  1. Georgia Institute of Technology, Atlanta, GA, USA

    Alexandra Boldyreva

  2. University of California at San Diego, La Jolla, CA, USA

    Daniele Micciancio

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Malavolta, G., Thyagarajan, S.A.K. (2019). Homomorphic Time-Lock Puzzles and Applications. In: Boldyreva, A., Micciancio, D. (eds) Advances in Cryptology – CRYPTO 2019. CRYPTO 2019. Lecture Notes in Computer Science(), vol 11692. Springer, Cham. https://doi.org/10.1007/978-3-030-26948-7_22

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  • DOI: https://doi.org/10.1007/978-3-030-26948-7_22

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