Compact dependent key generation methods for encryption-based subscription differentiation for scalable bit-streams

Subscription differentiation can be easily supported by deploying a scalable (prioritized) bit-stream and encrypting different parts of the bit-stream with various keys. Based on the subscription level, only the keys corresponding to the authorized part of the bit-stream are transmitted to the receiver. Since state-of-the-art scalable bit-streams offer a plethora of spatial, temporal and SNR resolutions, the number of keys to communicate for the various resolutions can be very large and variable. In this paper, two methods are proposed to significantly reduce the number of keys to be communicated by using dependent keys related by one-way functions. The first method is based on using separate one-way function chains for the keys for each scalability dimension. The second method allows simultaneous key progression along multiple dimensions by using special types of quasi-commutative one-way functions called one-way accumulators. The resultant one-way structure is named the accumulator mesh.