Patent ID: 6785390
Filing Date: 2004-08-31
Classification: H04L

Abstract:
A receiving apparatus for receiving data encrypted by an encryption key that is updated periodically, comprising:obtaining means for obtaining an initial value of the encryption key; generating means for generating a decryption key according to initial value of the encryption key; receiving means for receiving the encrypted data; reading means for reading a flag attached to the received encrypted data; detecting means for detecting changes in a state of said flag and a polarity of each said change; updating means for updating said decryption key in synchronization with each said change of said flag and in response to said polarity of each said change; storage means for storing versions of said decryption keys corresponding to said changed states of said flag; and decrypting means for decrypting the received encrypted data using one of said stored versions of said decryption keys corresponding to said flag attached to the received encrypted data.