We consider playing online games on peer-to-peer networks, without assuming servers that control the execution of a game. In such an environment, players may cheat the opponent by, for example, illegally replacing the cards in their hands. The aim of this paper is to examine a possibility of excluding such cheatings. We show that by employing cryptographic techniques, we can exclude some types of cheating at some level. Finally, based on our discussion, we implement the cheat-proof network “Gunjin-Shogi”, which is a variant of Japanese Chess.