,
Koji Nuida
Creative Commons Attribution 4.0 International license
Card-based cryptography is the art of cryptography using a deck of physical cards. While this area is known as a research area of recreational cryptography and is recently paid attention in educational purposes, there is no systematic study of the relationship between card-based cryptography and the other "conventional" cryptography. This paper establishes the first generic conversion from card-based protocols to private simultaneous messages (PSM) protocols, a special kind of secure multiparty computation. Our compiler supports "simple" card-based protocols, which is a natural subclass of finite-runtime protocols. The communication complexity of the resulting PSM protocol depends on how many cards are opened in total in all possible branches of the original card-based protocol. This result shows theoretical importance of such "opening complexity" of card-based protocols, which had not been focused in this area. As a consequence, lower bounds for PSM protocols imply those for simple card-based protocols. In particular, if there exists no PSM protocol with subexponential communication complexity for a function f, then there exists no simple card-based protocol with subexponential opening complexity for the same f.
@InProceedings{shinagawa_et_al:LIPIcs.STACS.2025.72,
author = {Shinagawa, Kazumasa and Nuida, Koji},
title = {{Card-Based Protocols Imply PSM Protocols}},
booktitle = {42nd International Symposium on Theoretical Aspects of Computer Science (STACS 2025)},
pages = {72:1--72:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-365-2},
ISSN = {1868-8969},
year = {2025},
volume = {327},
editor = {Beyersdorff, Olaf and Pilipczuk, Micha{\l} and Pimentel, Elaine and Thắng, Nguy\~{ê}n Kim},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2025.72},
URN = {urn:nbn:de:0030-drops-228975},
doi = {10.4230/LIPIcs.STACS.2025.72},
annote = {Keywords: Card-based cryptography, private simultaneous messages}
}