Modified twofish algorithm for increasing security and efficiency in the encryption of video signals

A new encryption system is presented for compressed video signals. It employs the twofish algorithm, recently proposed for standardization purposes, as the core cipher but, through simple modifications, it permits to achieve the very high security levels promised by the standard with reduced overhead and processing time. So the new method is particularly adapted for bandwidth limited applications operating in real time. For the sake of clarity, the proposal is tested on H.263+ coded signals, but it can be easily adapted to other formats, of MPEG-x or H.26x type. Performance evaluation is done off-line, by using a simulator, but also implemented on-line in a practical environment. A comparison is made with the previous systems.