The differential cryptanalysis method developed by E. Biham et al. presented a new index of cryptographic strength, i.e. signal to noise ratio (S/N). Their paper estimates S/N only for DES-like functions, i.e., cryptographic function based on iterating the same weak function n times. Other types such as including both stronger and weaker functions have not yet been examined. This paper examines the N-stage MULTI2 cipher algorithm to calculate S/N and shows there are many fast cipher algorithms having small S/N property.

For a method to control the microwave coupled lines with optically induced plasma effectively, we propose the selective mode-control method, which restricts controlled modes to a selected one. We analyzed the basic characteristics of coupled microstrip lines theoretically by using the spectral domain technique and indicated the effectiveness of this method with the aid of numerical results. Further, we designed an optically controlled change-over switch as an application of this method.