To provide an anti-tampering system having an enhanced security, which makes it difficult to analyze instruction codes of a key generation logic, encryption decryption processing, etc. executed in a terminal device while shortening an operation time.

The anti-tampering system comprises a terminal device 100 and an anti-tampering device 200 communicating with the terminal device. The terminal device transmits an instruction to generate an encrypting instruction for encryption object data existing in an input area, to the anti-tampering device, and the anti-tampering device transmits the encrypting instruction for encryption object data to the terminal device, and the terminal device executes the encrypting instruction and transfers encrypted data to an output area. The terminal device transmits a classification of a processor of the terminal device to the anti-tampering device together with the instruction to generate the encrypting instruction, and the anti-tampering device transmits the instruction to generate the encrypting instruction, to the terminal device only when the anti-tampering device can cope with the received classification of the processor of the terminal device.

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