Paper 2023/405

CaSCaDE: (Time-Based) Cryptography from Space Communications DElay

Carsten Baum, Technical University of Denmark
Bernardo David, IT University of Copenhagen
Elena Pagnin, Chalmers University of Technology
Akira Takahashi, J.P.Morgan AI Research & AlgoCRYPT CoE
Abstract

Time-based cryptographic primitives such as Time-Lock Puzzles (TLPs) and Verifiable Delay Functions (VDFs) have proven to be pivotal in several areas of cryptography. All existing candidate constructions, however, guarantee time-delays based on the average hardness of sequential computational problems. This means that any algorithmic or hardware improvement affects parameter choices and may turn deployed systems insecure. To address this issue, we investigate how to build time-based cryptographic primitives where delays depend on sources other than sequential computations: namely, transmission delays caused by sequential communication. We explore sequential communication delays that arise when sending a message through a constellation of satellites in Space. This setting has the advantage that distances between protocol participants are guaranteed as positions of satellites are observable from Earth, moreover delay lower bounds are unconditional and can be easily computed using the laws of Physics (no transmission travels faster than the speed of Light). We introduce proofs of sequential communication delay (SCD) in the Universal Composability framework, that can be used to convince a verifier that a message has accrued delay by traversing a path among a set of scattered satellites. With our SCD proofs we realize the first proposals of Publicly Verifiable TLPs and VDFs whose delay guarantees are rooted on physical limits, rather than ever-decreasing computational hardness. Finally, our notion of SCD paves the way to the first Delay Encryption construction not based on supersingular isogenies.

Metadata
Available format(s)
PDF
Publication info
Published elsewhere. Major revision. SCN 2024
Contact author(s)
cabau @ dtu dk
bernardo @ bmdavid com
elenap @ chalmers se
takahashi akira 58s @ gmail com
History
2024-07-05: last of 2 revisions
2023-03-21: received
See all versions
Short URL
https://ia.cr/2023/405
License
Creative Commons Attribution
CC BY

BibTeX

@misc{cryptoeprint:2023/405,
      author = {Carsten Baum and Bernardo David and Elena Pagnin and Akira Takahashi},
      title = {{CaSCaDE}: (Time-Based) Cryptography from Space Communications {DElay}},
      howpublished = {Cryptology {ePrint} Archive, Paper 2023/405},
      year = {2023},
      url = {https://eprint.iacr.org/2023/405}
}
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