Image processing device, tampering prevention method, and tampering detection method

A tampering prevention method executed by a computer, the tampering prevention method comprising:

• calculating, by a processor, frequency coefficients of an image;
• selecting a plurality of pairs of the frequency coefficients from the calculated frequency coefficients;
• generating a code based on a comparison result between an absolute value of a difference between the two frequency coefficients of each of the selected pairs and a threshold, and a magnitude relationship between the two frequency coefficients;
• and
• encrypting the generated code with a private key to generate a digital signature.

An image processing device comprising:

• a frequency calculation part configured to calculate frequency coefficients of an image subjected to tampering detection;
• a coefficient selection part configured to select a plurality of pairs of the frequency coefficients from the calculated frequency coefficients;
• a code generation part configured to generate a code based on a magnitude relationship between the two frequency coefficients of each of the selected pairs;
• and
• a signature verification part configured to acquire a digital signature and a public key, and compare a code obtained by decrypting the digital signature with the public key and the code generated by the code generation part to verify presence or absence of tampering with the image subjected to tampering detection.

A tampering detection method executed by a computer, the tampering detection method comprising:

• calculating, by a processor, frequency coefficients of an image subjected to tampering detection;
• selecting a plurality of pairs of the frequency coefficients from the calculated frequency coefficients;
• generating a code based on a magnitude relationship between the two frequency coefficients of each of the selected pairs;
• and
• acquiring a digital signature and a public key, and comparing a code obtained by decrypting the digital signature with the public key and the generated code to verify presence or absence of tampering with the image subjected to tampering detection.