Patent ID: 8281128

Claim:
A machine-implemented method of transporting an encrypted transport stream of multimedia content, the method comprising: dividing a transport stream of the multimedia content into a plurality of packets; receiving key information and first time information from information included in a selected packet from among the plurality of packets; determining encryption information from the key information and the first time information, according to a key derivation function, wherein the first time information is variable with time; encrypting the plurality of packets using the determined encryption information; and transporting the plurality of encrypted packets and the key information, wherein the determining the encryption information comprises selecting, as encryption information for a current packet, one of encryption information determined according to the key derivation function using the first time information included in a header of the current packet and the key information, and encryption information determined according to the key derivation function using the key information and the first time information included in a header of a packet closest to the current packet from among packets previous to the current packet and include the first time information.