Encrypted communication system that limits the damage caused when a secret key has been leaked

摘要

In an encrypted transmission system composed of one transmission apparatus 10 and twenty-eight reception apparatuses A1-G4 that are classified into seven groups A-G, two secret keys exclusively selected out of a total of fourteen secret keys are distributed beforehand to each group. The transmission apparatus 10 encrypts the same message M using one of the two secret keys distributed to each group and sends each group a message M encrypted with one of the group's secret keys. The reception apparatuses each decrypt the received cryptogram separately using each of the secret keys of group to which each reproduction apparatus belongs, judge whether either of the two decryption results conforms to a predetermined rule, and specify the correct decryption result.