Adaptive and composable multi-media transcoders

In this paper, a new construction of adaptive and composable transcoders from universally composabley secure (the uc-security) commitments is introduced and analyzed. Our transcoder is built on the top of scalable video coding standard, known as H.264/SVC. The idea behind of our implementation is simple: a base layer of streams is encoded by an extractable key while an enhanced layer of streams is encoded by an equivocable key of the underlying universally composable commitment scheme. We show that our construction reaches the UC-security in the presence of adaptive adversaries in the common reference string model assuming that the underlying Paillier´s public-key encryption scheme is semantically secure and the Damgård-Fazio-Nicolosi´s non-interactive protocol is zero-knowledge in the registered public-key model. Furthermore, if the underlying Paillier´s public-key encryption scheme is replaced by Damgård-Jurik´s length-flexible public key encryption scheme, then the derived adaptive and composable transcoder is length-flexible as well.