Doctor of Philosophy

dissertationCross layer system design represents a paradigm shift that breaks the traditional layer-boundaries in a network stack to enhance a wireless network in a number of di erent ways. Existing work has used the cross layer approach to optimize a wireless network in terms of packet scheduling, error correction, multimedia quality, power consumption, selection of modulation/coding and user experience, etc. We explore the use of new cross layer opportunities to achieve secrecy and e ciency of data transmission in wireless networks. In the rst part of this dissertation, we build secret key establishment methods for private communication between wireless devices using the spatio-temporal variations of symmetric-wireless channel measurements. We evaluate our methods on a variety of wireless devices, including laptops, telosB sensor nodes, and Android smartphones, with diverse wireless capabilities. We perform extensive measurements in real-world environments and show that our methods generate high entropy secret bits at a signi cantly faster rate in comparison to existing approaches. While the rst part of this dissertation focuses on achieving secrecy in wireless networks, the second part of this dissertation examines the use of special pulse shaping lters of the lterbank multicarrier (FBMC) physical layer in reliably transmitting data packets at a very high rate. We rst analyze the mutual interference power across subcarriers used by di erent transmitters. Next, to understand the impact of FBMC beyond the physical layer, we devise a distributed and adaptive medium access control protocol that coordinates data packet tra c among the di erent nodes in the network in a best e ort manner. Using extensive simulations, we show that FBMC consistently achieves an order-of-magnitude performance improvement over orthogonal frequency division multiplexing (OFDM) in several aspects, including packet transmission delays, channel access delays, and e ective data transmission rate available to each node in static indoor settings as well as in vehicular networks

Key Generation in Wireless Sensor Networks Based on Frequency-selective Channels - Design, Implementation, and Analysis

Key management in wireless sensor networks faces several new challenges. The scale, resource limitations, and new threats such as node capture necessitate the use of an on-line key generation by the nodes themselves. However, the cost of such schemes is high since their secrecy is based on computational complexity. Recently, several research contributions justified that the wireless channel itself can be used to generate information-theoretic secure keys. By exchanging sampling messages during movement, a bit string can be derived that is only known to the involved entities. Yet, movement is not the only possibility to generate randomness. The channel response is also strongly dependent on the frequency of the transmitted signal. In our work, we introduce a protocol for key generation based on the frequency-selectivity of channel fading. The practical advantage of this approach is that we do not require node movement. Thus, the frequent case of a sensor network with static motes is supported. Furthermore, the error correction property of the protocol mitigates the effects of measurement errors and other temporal effects, giving rise to an agreement rate of over 97%. We show the applicability of our protocol by implementing it on MICAz motes, and evaluate its robustness and secrecy through experiments and analysis.Comment: Submitted to IEEE Transactions on Dependable and Secure Computin

Software Grand Exposure: SGX Cache Attacks Are Practical

Side-channel information leakage is a known limitation of SGX. Researchers have demonstrated that secret-dependent information can be extracted from enclave execution through page-fault access patterns. Consequently, various recent research efforts are actively seeking countermeasures to SGX side-channel attacks. It is widely assumed that SGX may be vulnerable to other side channels, such as cache access pattern monitoring, as well. However, prior to our work, the practicality and the extent of such information leakage was not studied. In this paper we demonstrate that cache-based attacks are indeed a serious threat to the confidentiality of SGX-protected programs. Our goal was to design an attack that is hard to mitigate using known defenses, and therefore we mount our attack without interrupting enclave execution. This approach has major technical challenges, since the existing cache monitoring techniques experience significant noise if the victim process is not interrupted. We designed and implemented novel attack techniques to reduce this noise by leveraging the capabilities of the privileged adversary. Our attacks are able to recover confidential information from SGX enclaves, which we illustrate in two example cases: extraction of an entire RSA-2048 key during RSA decryption, and detection of specific human genome sequences during genomic indexing. We show that our attacks are more effective than previous cache attacks and harder to mitigate than previous SGX side-channel attacks

Secure key design approaches using entropy harvesting in wireless sensor network: A survey

Physical layer based security design in wireless sensor networks have gained much importance since the past decade. The various constraints associated with such networks coupled with other factors such as their deployment mainly in remote areas, nature of communication etc. are responsible for development of research works where the focus is secured key generation, extraction, and sharing. Keeping the importance of such works in mind, this survey is undertaken that provides a vivid description of the different mechanisms adopted for securely generating the key as well its randomness extraction and also sharing. This survey work not only concentrates on the more common methods, like received signal strength based but also goes on to describe other uncommon strategies such as accelerometer based. We first discuss the three fundamental steps viz. randomness extraction, key generation and sharing and their importance in physical layer based security design. We then review existing secure key generation, extraction, and sharing mechanisms and also discuss their pros and cons. In addition, we present a comprehensive comparative study of the recent advancements in secure key generation, sharing, and randomness extraction approaches on the basis of adversary, secret bit generation rate, energy efficiency etc. Finally, the survey wraps up with some promising future research directions in this area