Since a conventional information processing apparatus includes a plurality of semiconductor devices, there is a problem that sensitive information may reside on a system bus in the apparatus or a semiconductor memory device serving as main memory therein. To obviate this problem, each information processing apparatus has a CPU which includes a microprocessor, a cryptographic processing algorithm ROM, a cryptographic processing hardware circuit, a RAM, a key custody area, and an external bus controller, which are all integrated on a single semiconductor chip. Thus, encryption/decryption processing is carried out only in the CPU, and internal operations of the CPU are made non-analyzable from an external signal of the CPU.