The Six-Card Trick: Secure Computation of Three-Input Equality

Secure computation enables parties having secret inputs to compute some function of their inputs without revealing inputs beyond the output. It is known that secure computation can be done by using a deck of physical cards. The five-card trick proposed by den Boer in 1989 is the first card-based protocol, which computes the logical AND function of two inputs. In this paper, we design a new protocol for the three-input equality function using six cards, which we call the six-card trick.