Common graph algorithms in computer science mostly assume that there’s no cycle in graph structure. On the other hand, the cyclic authentication proves to be a great tool for security enhancement indeed. A cycle means eternity. When a program meets the cycle, it never ends. We can apply the mechanism to ameliorate encryption algorithm. For instance, suppose that there are three individual services A, B and C. Service A has the password to access B, B has that of C and C has that of A. It’s a cyclic password lock. No one can break the cycle unless every service is completely exploited by attackers. Excluding social engineering cases, the countermeasure proves no way to break up. It’s a very subject worthy to consider.