Encryption device and encryption system

An encryption system including an encryption apparatus for encrypting a data piece that is smaller than a unit length for encryption and a decryption apparatus for decrypting the encrypted data piece,

• the encryption apparatus comprising:
• a storage unit operable to store therein management information indicating a used area within an encryption area defined based on the unit length, the used area being an area already used for encryption;
• an encryption unit operable, when encrypting a new data piece that is smaller than the unit length, to generate encrypted data by adding the new data piece to an unused area within the encryption area with reference to the management information, the unused area being an area not used for encryption;
• and
• a control unit operable to update the management information to include an area for the new data piece into the used area after the encryption unit generates the encrypted data, and output the encrypted data together with the updated management information to the decryption apparatus, and
• the decryption apparatus comprising:
• a decryption unit operable to decrypt the encrypted data input from the encryption apparatus, and extracts, from the decrypted data, a data piece existing within an area based on the used area indicated by the management information.

An encryption method for encrypting a data piece that is smaller than a unit length for encryption, comprising the steps of:

• storing management information indicating a used area within an encryption area defined based on the unit length, the used area being an area already used for encryption;
• when encrypting a new data piece that is smaller than the unit length, generating encrypted data by adding the new data piece to an unused area within the encryption area with reference to the management information, the unused area being an area not used for encryption;
• and
• updating the management information to include an area for the new data piece into the used area, after the generation of the encrypted data.

A computer program for controlling an encryption apparatus for encrypting a data piece that is smaller than a unit length for encryption, the computer program causing a computer in the encryption apparatus to execute the steps of:

• storing management information indicating a used area within an encryption area defined based on the unit length, the used area being an area already used for encryption;
• when encrypting a new data piece that is smaller than the unit length, generating encrypted data by adding the new data piece to an unused area within the encryption area with reference to the management information, the unused area being an area not used for encryption;
• and
• updating the management information to include an area for the new data piece into the used area, after the generation of the encrypted data.

An integrated circuit for use in an encryption apparatus for encrypting a data piece that is smaller than a unit length for encryption, comprising:

• a storage unit operable to store therein management information indicating a used area within an encryption area defined based on the unit length, the used area being an area already used for encryption;
• an encryption unit operable, when encrypting a new data piece that is smaller than the unit length, to generate encrypted data by adding the new data piece to an unused area within the encryption area with reference to the management information, the unused area being an area not used for encryption;
• and
• a control unit operable to update the management information to include an area for the new data piece into the used area, after the generation of the encrypted data.