Data management device, system, re-encryption device, data sharing device, and storage medium

A system comprising a data sharing device and a re-encryption device,

• the data sharing device comprising:
• a first encrypted data storage device for storing first encrypted data obtained by encrypting plain text data with a first public key of a first user device;
• a first conversion key storage device for storing a conversion key generated from a first private key corresponding to the first public key and a second private key of the first user device;
• an encrypted data conversion device for converting the first encrypted data into second encrypted data with the conversion key;
• a second encrypted data storage device for storing the second encrypted data, and
• the re-encryption device comprising:
• a first re-encryption key storage device for storing a first re-encryption key for re-encrypting the first encrypted data without decrypting to obtain first re-encrypted data decryptable with a private key of a second user device;
• a second conversion key storage device for storing the conversion key;
• a re-encryption key conversion device for converting the first re-encryption key into a second re-encryption key with the conversion key in the second conversion key storage device;
• and
• a second re-encryption key storage device for storing the second re-encryption key,
• wherein the second encrypted data is identical to encrypted data obtained by encrypting the plain text data with a second public key corresponding to the second private key, and
• the second re-encryption key is a re-encryption key for re-encrypting the second encrypted data without decrypting to obtain second re-encrypted data decryptable with the private key of the second user device.

A re-encryption device configured to communicate with a data sharing device that stores first encrypted data obtained by encrypting plain text data with a first public key of a first user device,

• the data sharing device also being a device that stores a conversion key generated from a first private key corresponding to the first public key and a second private key of the first user device, converts the first encrypted data into second encrypted data with the conversion key, and stores the second encrypted data, and comprising:
• a first re-encryption key storage device for storing a first re-encryption key for re-encrypting the first encrypted data without decrypting to obtain first re-encrypted data decryptable with a private key of a second user device;
• a second conversion key storage device for storing the conversion key;
• a re-encryption key conversion device for converting the first re-encryption key into a second re-encryption key with the conversion key in the second conversion key storage device;
• and
• a second re-encryption key storage device for storing the second re-encryption key,
• wherein the second encrypted data is identical to encrypted data obtained by encrypting the plain text data with a second public key corresponding to the second private key, and
• the second re-encryption key is a re-encryption key for re-encrypting the second encrypted data without decrypting to obtain second re-encrypted data decryptable with the private key of the second user device.

A data sharing device configured to communicate with a re-encryption device, the data sharing device comprising:

• a first encrypted data storage device for storing first encrypted data obtained by encrypting plain text data with a first public key of a first user device;
• a first conversion key storage device for storing a conversion key generated from a first private key corresponding to the first public key and a second private key of the first user device;
• an encrypted data conversion device for converting the first encrypted data into second encrypted data with the conversion key;
• a second encrypted data storage device for storing the second encrypted data,
• wherein the re-encryption device is configured to store a first re-encryption key for re-encrypting the first encrypted data without decrypting and obtaining first re-encrypted data decryptable with a private key of a second user device, store the conversion key, convert the first re-encryption key into a second re-encryption key with the conversion key, and store the second re-encryption key,
• the second encrypted data is identical to encrypted data obtained by encrypting the plain text data with a second public key corresponding to the second private key, and
• the second re-encryption key is a re-encryption key for re-encrypting the second encrypted data without decrypting to obtain second re-encrypted data decryptable with the private key of the second user device.

A non-transitory computer readable storage medium storing a program to cause a processor to perform processing, the program which is used by a re-encryption device configured to communicate with a data sharing device that stores first encrypted data obtained by encrypting plain text data with a first public key of a first user device, the re-encryption device comprising a storage device and the processor,

• the data sharing device also being a device that stores a conversion key generated from a first private key corresponding to the first public key and a second private key of the first user device, converts the first encrypted data into second encrypted data with the conversion key, and stores the second encrypted data, and
• the processing comprising:
• writing, in the storage device, a first re-encryption key for re-encrypting the first encrypted data without decrypting to obtain first re-encrypted data decryptable with a private key of a second user device;
• writing the conversion key in the storage device;
• converting the first re-encryption key into a second re-encryption key with the conversion key in the storage device;
• and
• writing the second re-encryption key in the storage device,
• wherein the second encrypted data is identical to encrypted data obtained by encrypting the plain text data with a second public key corresponding to the second private key, and
• the second re-encryption key is a re-encryption key for re-encrypting the second encrypted data without decrypting to obtain second re-encrypted data decryptable with the private key of the second user device.

A non-transitory computer readable storage medium storing a program to cause a processor to perform processing, the program which is used by a data sharing device configured to communicate with a re-encryption device, the data sharing device comprising a storage device and the processor,

• the processing comprising:
• writing, in the storage device, first encrypted data obtained by encrypting plain text data with a first public key of a first user device in the storage device;
• writing a conversion key generated from a first private key corresponding to the first public key and a second private key of the first user device in the storage device;
• converting the first encrypted data into second encrypted data with the conversion key;
• and
• writing the second encrypted data in the storage device,
• wherein the re-encryption device is configured to store a first re-encryption key for re-encrypting the first encrypted data without decrypting and obtaining first re-encrypted data decryptable with a private key of a second user device, store the conversion key, convert the first re-encryption key into a second re-encryption key with the conversion key, and store the second re-encryption key,
• the second encrypted data is identical to encrypted data obtained by encrypting the plain text data with a second public key corresponding to the second private key, and
• the second re-encryption key is a re-encryption key for re-encrypting the second encrypted data without decrypting to obtain second re-encrypted data decryptable with the private key of the second user device.