The Optimal Carrier-Secret Ratio for Wireless Covert Channels Based on Constellation Shaping Modulation

Wireless covert communication is an emerging communication technique that prevents eavesdropping. This paper considers the bit error ratio (BER) problem of covert communication based on constellation shaping modulation (CSM). The impact of carrier-secret ratio (CSR) on BER is studied and the approximate solution of optimal CSR is obtained. Then, we extended the conclusion to typical communication scenarios with one and more relays where the undetectability and reliability were analyzed and inspected. It is proved that there also exists the optimal CSR in scenarios with relays. Additionally, it is found that the undetectability under the constraints of constant total power depends on the eavesdropper’s position, and we found an undetectability deterioration area (UDA) in the scenario of relays. Simulation results show the existence of optimal CSR and its impact on transmission performance.

Speculative taint tracking (STT)

Speculative execution attacks present an enormous security threat, capable of reading arbitrary program data under malicious speculation, and later exfiltrating that data over microarchitectural covert channels. This paper proposes speculative taint tracking (STT), a high security and high performance hardware mechanism to block these attacks. The main idea is that it is safe to execute and selectively forward the results of speculative instructions that read secrets, as long as we can prove that the forwarded results do not reach potential covert channels. The technical core of the paper is a new abstraction to help identify all micro-architectural covert channels, and an architecture to quickly identify when a covert channel is no longer a threat. We further conduct a detailed formal analysis on the scheme in a companion document. When evaluated on SPEC06 workloads, STT incurs 8.5% or 14.5% performance overhead relative to an insecure machine.

A Noninterference Model for Mobile OS Information Flow Control and Its Policy Verification

Mobile operating systems such as Android are facing serious security risk. First, they have a large number of users and store a large number of users’ private data, which have become major targets of network attack; second, their openness leads to high security risks; third, their coarse-grained static permission control mechanism leads to a large number of privacy leaks. Recent decentralized information flow control (DIFC) operating systems such as Asbestos, HiStar, and Flume dynamically adjust the label of each process. Asbestos contains inherent covert channels due to this implicit label adjustment. The others close these covert channels through the use of explicit label change, but this impedes communication and increases performance overhead. We present an enhanced implicit label change model (EILCM) for mobile operating systems that can close the known covert channel in these models with implicit label change and supports dynamic constraints on tags for separation of duty. We also formally analyze the reasons why EILCM can close the known covert channels and prove that abstract EILCM systems have the security property of noninterference with declassification by virtue of the model checker tool FDR. We also prove that the problem of EILCM policy verification is NP-complete and propose a backtrack-based search algorithm to solve the problem. Experiments are presented to show that the algorithm is effective.