Patent ID: 8233621

Claim:
A method comprising: receiving a slice comprising a plurality of macroblocks by a transmitter having a processor, a memory, an I/O interface and an encrypter; selecting an encryption key based at least in part on a relative importance of secure transmission of the macroblocks, the encryption key comprising: if the importance is high, a master key; if the importance is medium, a first key derivable by applying a one-way function to the master key; and if the importance is low, a second key derivable by applying the one-way function to the first key; and encrypting, by the transmitter, the slice using the encryption key for transmission to one or more receivers having a processor, a memory, an I/O interface and a decryptor, wherein the relative importances of secure transmission of I frame slices and headers, P frame slices which contain more than a first predetermined amount (α) of I-macroblocks, and B frame slices which contain more than a second predetermined amount (β) of I-macroblocks, are high, medium, and low, respectively, and the relative importance of other slices is lowest.