Image encryption apparatus and image decryption apparatus

An image encryption method executed by an image encryption apparatus for encrypting image data of a document, said method comprising:

• receiving area data indicating an encryption area of the document;
• receiving level data indicating an authority level for the encryption area indicated by the area data received in the operation of receiving area data;
• generating an encryption key corresponding to the authority level indicated by the level data received in the operation of receiving level data;
• implanting check data in the image data of the document within the encryption area, said check data being detected in verifying whether or not encrypted image data in the encryption area is appropriately decrypted through decryption;
• and
• encrypting the image data of the document within the encryption area with the encryption key corresponding to the authority level for the encryption area, said image data being implanted with the check data.

An image decryption method executed by an image decryption apparatus for decrypting encrypted image data, said method comprising:

• determining a maximum authority level, said image decryption apparatus decrypting the encrypted image data of authority levels lower than or equal to the maximum authority level;
• generating decryption keys corresponding to all authority levels lower than or equal to the maximum authority level determined in the operation of determining a maximum authority level;
• decrypting the encrypted image data within an encryption area with each of the decryption keys to generate a set of decrypted image data;
• trying to detect check data from each of the set of decrypted image data, said check data being implanted in the encrypted image data through encryption;
• and
• selecting, as appropriately decrypted image data for the encryption area, decrypted image data from which the check data has been detected