Information processing device, encryption method of instruction code, and decryption method of encrypted instruction code

Abstract

It is possible to achieve the protection of software with reduced overhead. For example, a memory for storing an encrypted code prepared in advance and a decryptor module for decrypting the code are provided. The decryptor module includes, for example, a three-stage pipeline and a selector for selecting one output from the outputs of each stage of the pipeline. When a branch instruction is issued and subsequent inputs of the pipeline are in the order of CD', CD′, . . . , the decryptor module outputs a first decrypted code by performing a one-stage pipeline process to CD′. Next, the decryptor module outputs a second decrypted code by performing a two-stage pipeline process to CD′, and the decryptor module outputs a third decrypted code by performing a three-stage pipeline process to CD′(and subsequent codes). Therefore, in particular, the overhead to CD′can be reduced.