Patent ID: 6834111
Filing Date: 2004-12-21
Classification: H04H,H04L

Abstract:
A data transmitting and receiving method comprising the steps of:on a transmission side, encrypted digital data obtained by performing a first encryption process on digital data using a work key, and an encrypted work key obtained by performing a second encryption process on the work key using a control key, are transmitted, and on a reception side, the encrypted work key is received and decrypted using the control key obtained by performing an authentication and key exchange process with the transmission side, and the encrypted digital data is received and decrypted using the decrypted work key, thereby obtaining the digital data, on said transmission side, the control key is periodically or non-periodically updated, an identifier identifying the control key is assigned for each control key; and on said reception side, when a reception process is suspended and then resumed, it is determined whether or not the control key has been updated while the reception process is being suspended by referring to the identifier transmitted from the transmission side, and, when it is determined that the control key has been updated, the authentication and key exchange process is performed again, thereby obtaining the updated control key; wherein said reception side requests the transmission side to transmit the identifier when the reception process is suspended and then resumed; and said transmission side transmits the identifier when the authentication and key exchange process is performed, and also transmits the identifier in response to the request; the reception side receives the identifier transmitted from the transmission side, and the reception side does not perform the authentication and key exchange process, based on the received identifier and determining that the control key has not been updated.