Security Analysis of Generalized Confidentialmodulation for Quantum Communication

We propose a new evaluation method for‘generalized confidential modulation(GCM)’ for quantum communication. Confidential modulationrealizes a secret communication by using secret information for modulationand noise in a channel. Y-00 is one of the famous methods of GCM forquantum communication. The existing evaluation methods for GCM arebased on stream ciphers. They can estimate its analytical security andthe evaluation depends on the security status of pseudo random numbergenerator (PRNG) which controls the modulation. On the other hand,our method is based on mode of operation for block ciphers and clears theweaknesses from structural viewpoint. Using our method, we can comparethe security of different GCM structures. Our method of security evaluationand comparison does not depend on the security status of PRNG.From the results of our evaluation, we conclude that the security of GCMis limited to computational security.