Patent ID: 8078874

Claim:
A method of transmitting data using authentication between a first device and a second device, the method comprising: encrypting a certificate of the first device using a shared key shared by the first device and the second device, and transmitting the encrypted certificate of the first device to the second device; receiving at the first device, authentication key generation information for the first device for generating an authentication key, if it is determined that the certificate of the first device is valid and not revoked; determining whether the authentication key generation information for the first device has been altered, wherein the determining of whether the authentication key generation information for the first device has been altered comprises: receiving an electronic signature of the authentication key generation information, wherein the electronic signature comprises data in which the authentication key generation information for the first device and a hash value of the authentication key generation information for the first device are encrypted using a secret key of the second device; decrypting the encrypted authentication key generation information for the first device using a public key of the second device included in the certificate of the second device, and comparing a hash value of the authentication key generation information for the first device obtained by the decrypting the encrypted authentication key generation information for the first device, and the hash value of the authentication key generation information for the first device included in the electronic signature; generating at the first device, a first random number of the first device; generating at the first device, the authentication key based on the first random number and the authentication key generation information for the first device; encrypting content data using the authentication key, at the first device; and transmitting the encrypted content data from the first device to the second device.