Image encrypting device, image decrypting device and method

An image decrypting device for decrypting an encrypted image including an image encrypted into an original image, the image decrypting device comprising:

• a computer configured to:
• input the encrypted image as image data;
• detect a position of an encryption region that is a region, in which an image is encrypted in the encrypted image, by analyzing the encrypted image;
• restore a pixel value of the image of the encryption region to a pixel value before being converted by a first conversion process for converting a pixel value of the image of the encryption region at certain cycles in a horizontal direction and a vertical direction of the image of the encryption region, by executing a second conversion process reverse to the first conversion process in order to identify the position of the encryption region on the basis of information about the position of the encryption region;
• extract encryption key associated information, which is information about an encryption key embedded in the image of the encryption region, from the restored image of the encryption region;
• decrypt a decryption key, which is used to decrypt the image of the encryption region, from the encryption key associated information by using a first private key pairing with a first public key used to generate the encryption key associated information;
• decrypt an original image by decrypting the image of the encryption region by using the decrypted decryption key;
• and
• output the original image in a predetermined method.

An image encrypting method for encrypting an image, the image encrypting method comprising:

• inputting image data to be encrypted;
• specifying an encryption region to be encrypted in the image data;
• converting the specified encryption region into a first image by using an encryption key;
• obtaining a public key of a transmission destination of the data to be encrypted;
• encrypting the encryption key by using the obtained public key;
• embedding encryption key associated information, which is information about the encrypted encryption key, in the first image to convert the encryption region into a second image;
• converting a pixel value of the second image at certain cycles in a horizontal direction and a vertical direction of the second image to convert the encryption region into a third image;
• and
• outputting an encrypted image, which is obtained by converting an image of the encryption region into the third image in the input image to be encrypted, in a predetermined method.

An image decrypting method for decrypting an encrypted image including an image encrypted into an original image, the image decrypting method comprising:

• inputting the encrypted image as image data;
• detecting a position of an encryption region that is a region, in which an image is encrypted in the encrypted image, by analyzing the encrypted image;
• restoring a pixel value of the image of the encryption region to a pixel value before being converted by a first conversion process for converting a pixel value of the image of the encryption region at certain cycles in a horizontal direction and a vertical direction of the image of the encryption region, by executing a second conversion process reverse to the first conversion process in order to identify the position of the encryption region on the basis of information about the detected position of the encryption region;
• extracting encryption key associated information, which is information about an encryption key embedded in the image of the encryption region, from the restored image of the encryption region;
• decrypting a decryption key, which is used to decrypt the image of the encryption region, from the encryption key associated information by using a first private key pairing with a first public key used to generate the extracted encryption key associated information;
• decrypting the original image by decrypting the image of the encryption region by using the decrypted decryption key;
• and
• outputting the original image in a predetermined method.

A storage medium not including a signal, storing an image encrypting program for causing a computer, in order to encrypt an image, to execute a process comprising:

• inputting image data to be encrypted;
• specifying an encryption region to be encrypted in the image data;
• converting the encryption region into a first image by using an encryption key;
• obtaining a public key of a transmission destination of the data to be encrypted;
• encrypting the encryption key by using the public key;
• embedding encryption key associated information, which is information about the encrypted encryption key, in the first image to convert the encryption region into a second image;
• converting a pixel value of the second image at certain cycles in a horizontal direction and a vertical direction of the second image to convert the encryption region into a third image;
• and
• outputting an encrypted image, which is obtained by converting an image of the encryption region into the third image in the image data, in a predetermined method.

A storage medium not including a signal, storing an image decrypting program for causing a computer, in order to decrypt an encrypted image including an image encrypted into an original image, to execute a process comprising:

• inputting the encrypted image as image data;
• detecting a position of an encryption region that is a region, in which an image is encrypted in the encrypted image, by analyzing the encrypted image;
• restoring a pixel value of an image of the encryption region to a pixel value before being converted by a first conversion process for converting a pixel value of the image of the encryption region at certain cycles in a horizontal direction and a vertical direction of the image of the encryption region, by executing a second conversion process reverse to the first conversion process in order to identify the position of the encryption region on the basis of information about the position of the encryption region;
• extracting encryption key associated information, which is information about an encryption key embedded in the image of the encryption region, from the restored image of the encryption region;
• decrypting a decryption key, which is used to decrypt the image of the encryption region, from the encryption key associated information by using a first private key pairing with a first public key used to generate the encryption key associated information;
• decrypting the original image by decrypting the image of the encryption region by using the decrypted decryption key;
• and
• outputting the original image in a predetermined method.