  Ball sort puzzle is a popular logic puzzle consisting of several bins
containing balls of multiple colors. Each bin works like a stack; a ball has to
follow the last-in first-out order. The player has to sort the balls by color
such that each bin contains only balls of a single color. In this paper, we
propose a physical zero-knowledge proof protocol for the ball sort puzzle using
a deck of playing cards, which enables a prover to physically show that he/she
knows a solution with $t$ moves of the ball sort puzzle without revealing it.
Our protocol is the first zero-knowledge proof protocol for an interactive
puzzle involving moving objects.
