US Patent 6970561 Encryption and decryption with endurance to cryptanalysis

An encrypting apparatus includes an encrypting operation section, a determining section and a control section. The encrypting operation section carries out an encrypting operation to a plaintext using intermediate data at each of a plurality of encrypting stages of the encrypting operation to produce a ciphertext. The encrypting operation section outputs encrypting stage data indicating an encrypting state at each of the plurality of processing stages. The determining section determines whether the encrypting operation at a next encrypting stage should be changed, based on the encrypting stage data at a current encrypting stage from the encrypting operation section. The control section changing the encrypting operation at the next encrypting stage when it is determined that the encrypting operation at the next encrypting stage should be changed.