International Association for Cryptologic Research

International Association
for Cryptologic Research


Homomorphic Time-Lock Puzzles and Applications

Giulio Malavolta
Sri Aravinda Krishnan Thyagarajan
DOI: 10.1007/978-3-030-26948-7_22 (login may be required)
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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.
Video from CRYPTO 2019
  title={Homomorphic Time-Lock Puzzles and Applications},
  booktitle={Advances in Cryptology – CRYPTO 2019},
  series={Lecture Notes in Computer Science},
  author={Giulio Malavolta and Sri Aravinda Krishnan Thyagarajan},