The key idea of dynamic spectrum access (DSA) networks is to allow the secondary, unlicensed users to detect and use unused portions of the spectrum (white spaces) opportunistically. The two main constraints in the design of DSA networks is to make sure that this opportunistic access is done without any disruption of service to the primary users and without any modifications to the primaries themselves. Most architectures and protocols for DSA networks in the literature assume that all parties are honest and that there are no attackers. Recently (IEEE ICC, CogNet 2008) we demonstrated the failure of this approach by showing that an attacker can manipulate messages to convince the parties involved in the protocol to make incorrect spectrum decisions. In this paper, we consider spectrum decision protocols in clustered infrastructure-based dynamic spectrum access networks where the spectrum decision in each cluster is coordinated by some central authority. We propose an efficient and provably secure protocol that can be used to protect the spectrum decision process against a malicious adversary.

Encryption is one of the fundamental technologies that is used in digital rights management. Unlike ordinary computer applications, multimedia applications generate large amounts of data that has to be processed in real time. So, a number of encryption schemes for multimedia applications have been proposed in recent years. We analyze the following proposed methods for multimedia encryption: key-based multiple Huffman tables (MHT), arithmetic coding with key-based interval splitting (KSAC), and randomized arithmetic coding (RAC). Our analysis shows that MHT and KSAC are vulnerable to low complexity known- and/or chosen-plaintext attacks. Although we do not provide any attacks on RAC, we point out some disadvantages of RAC over the classical compress-then-encrypt approach.