Card-Based Cryptography Meets 3D Printer

Card-based protocols perform cryptographic functionalities, such as secure computations, using a deck of cards. Basically, these protocols are supposed to be implemented by humans’ manipulating physical cards. This paper is the first attempt to make use of a 3D printer for better physical implementations of card-based protocols: we have designed and fabricated a couple of physical devices using a 3D printer that are useful for humans to implement protocols. The first device we created is the “five-card-trick turner,” which can turn over five cards simultaneously in an amusing manner; this operation appears in the final step of the five-card trick, which is the most famous card-based protocol. The second device we created is a special card box for storing a pile of cards, whose concept was proposed in 2015 but the device had not been created in reality thus far. The special boxes can be used for implementing complex shuffles that seem difficult to implement only by hand. Furthermore, we propose another use of these special boxes so that we can efficiently perform secure computations of symmetric functions.