Method for transmission/reception of contents usage right information in encrypted form, and device thereof

A content usage right information receiving device for receiving license data containing a content key for decrypting encrypted content data from a content usage right information providing device, the content usage right information receiving device comprising:

• a processor;
• a memory having a program, when executed, causing the processor to perform the following functions:
• a certificate output function for outputting a certificate containing a first public key of the content usage right information receiving device;
• an interface function for transmitting the certificate to the content usage right information providing device and receiving from the content usage right information providing device an encrypted first symmetric key;
• a first decryption function for decrypting the encrypted first symmetric key by using a first private key corresponding to the first public key and acquiring a first symmetric key;
• a generating function for generating a second symmetric key;
• and
• a first encryption function for concatenating the second symmetric key and a second public key of the content usage right information receiving device, and encrypting a concatenated key by using the first symmetric key and creating an encrypted second symmetric key, wherein
• the interface function transmits the second encrypted second symmetric key to the content usage right information providing device and receives first encrypted license data from the content usage right information providing device,
• the processor further performs the following functions:
• a second decryption function for decrypting the first encrypted license data by using the second symmetric key and acquiring second encrypted license data;
• and
• a third decryption function for acquiring a shared key and license data from the second encrypted license data, and
• after the first symmetric key and the shared key are shared between the content usage right information providing device and the content usage right information receiving device,
• the generating function generates a new second symmetric key,
• the first encryption function encrypts the new second symmetric key by using the first symmetric key and creating an encrypted second symmetric key,
• the interface function transmits the encrypted second symmetric key to the content usage right information providing device and receives first encrypted license data,
• the second decryption function decrypts the first encrypted license data by using the second symmetric key and acquires second encrypted license data, and
• the third decryption function decrypts the second encrypted license data by using the shared key and acquires license data.