The Sybil attack has devastating effect on many distributed decision protocols such as voting: By disguising with multiple identities, a Sybil attacker can amplify his impact on the final outcome. A cooperative spectrum sensing protocol, which aims to enhance the sensing performance over the individual sensing protocols, is a kind of cooperative decision protocol. If not carefully designed, cooperative spectrum sensing can also be very vulnerable to the false-reporting Sybil attack, in which an attacker seeks to degrade the sensing performance by submitting multiple incorrect measurements using multiple identities. In this paper, we exploit the attacker's limited radio resources and propose a Sybil-resilient clustering mechanism, and adopt it as the basis of a secure cluster-based cooperative sensing protocol. We perform extensive simulation and show that naïve soft data combination and statistics-based false-report-resilient cooperative sensing protocols are susceptible to the Sybil attack; however, our proposed protocol can still provide reasonable sensing outcome despite the presence of Sybil attackers.

Spectrum sensing is one of the most important enabling techniques on which to build a cognitive radio network. However, previously proposed techniques often have shortcomings in non-ideal environments: 1) An energy detector is simple but cannot perform in face of uncertain noise power; 2) A matched filter is the optimal detector, but performs poorly with clock drifts; 3) Eigenvalue-based blind feature detectors show great promise, but cannot detect signals that are noise-like; and 4) Above protocols all rely on field survey to determine the proper decision thresholds. We propose HIPSS and its extension Δ-HIPSS that are based on the Hermitian-inner-product of two observations acquired by a wireless receiver over multiple radio paths. HIPSS and Δ-HIPSS are lightweight and through extensive analysis and evaluation, we show that 1) HIPSS and Δ-HIPSS are robust in the presence of noise power uncertainties; 2) HIPSS and ΔHIPSS require neither a much longer observation duration nor complex computation compared to an energy detector in ideal setting; 3) HIPSS and Δ-HIPSS can detect noise-like primary signals; and 4) Δ-HIPSS can reliably return sensing decisions without necessitating any field surveys.

Since a transmitter can only be at one location at a time, a jammer must jam in a narrowband fashion in the spatial domain. We propose JIM-Beam, a narrowband jamming-resilient flooding protocol that randomizes the orientation of a node's directional antenna over time. We use ns-2 simulations to show that JIM-Beam provides improvements in packet delivery ratio over flooding naively and flooding using the uncoordinated frequency hopping protocol.

In this demonstration, we present a working prototype that uses an Anisotropic Magnetoresistive (AMR) sensor array to estimate the electricity usage on individual branches of an electricity panel. Our design enables the general public to retrofit an electricity panel: one simply needs to attach a compact AMR sensor array onto the panel. Our system can then exploit the inherent power patterns of electric loads to automatically infer the system parameters and estimate the per-branch currents accurately. Even for branches carrying small loads (e.g., a 30W fan), the estimation error of our system is below 10%.

Substantial effort has been invested on secure location verification in hope to enable mobile wireless systems to optimize system performance or securely confer rights based on the participants' locations. However, most previous studies do not address the impact of, and are often susceptible to, collusion attacks in which adversaries share their private keys. In this paper, we propose a secure multilateration scheme. Given the same processing delay, detection threshold, and assuming zero synchronization error between verifiers, our proposed scheme achieves the highest rate of false-location detection by any verification system based solely on time-of-flight measurements. We also show that our scheme is resilient to collusion attacks if the verification system can detect the distance enlargement attack. We propose using other physical measurements to mitigate the distance enlargement, and thus also the collusion, attacks. To the best of our knowledge, this is the first attempt to prevent collusion attacks by mitigating the distance enlargement attack.

In a Vehicular Ad hoc NETwork (VANET), vehicles broadcast safety messages disclosing their trajectory information in order to warn drivers of impending accidents. Precise location information needed for these safety applications, combined with the need to exclude attackers through the use of authentication, creates a significant privacy risk. One method proposed to improve privacy is the use of many pseudonyms, and changing pseudonyms while in a mix zone where all other vehicles also change pseudonyms. Previous work has evaluated the effectiveness of mix zones using traces generated based on traffic theory. In this paper, we analyze the privacy obtainable from using mix zones in VANETs based on actual recordings of vehicle movements. We choose rank instead of entropy as our privacy metric because, as we will show, entropy is difficult to measure in our scenarios.

Wireless communication systems are often susceptible to the jamming attack where adversaries attempt to overpower transmitted signals by injecting a high level of noise. Jamming is difficult to mitigate in broadcast networks because transmitting and receiving are inherently symmetric operations: A user that possesses the key to decode a transmission can also use that key to jam the transmission. We describe a code tree system that provides input to the physical layer and helps the physical layer circumvent jammers. In our system, the transmitter has more information than any proper subset of receivers. Each receiver cooperates with the transmitter to detect any jamming that affects that receiver. In the resulting system, each benign user is guaranteed to eliminate the impact of the attacker after some finite number of losses with arbitrarily high probability. We show that any system that relies on only using spreading code, and no other physical factors, to mitigate jamming must use at least$j+1$codes, where$j$is the number of jammers. We then propose an optimized scheme that is power-efficient: Each transmission is sent on at most$2j+1$codes simultaneously. Finally, we demonstrate that our scheme approaches the best possible performance by performing an extensive analysis of the system using both event-driven ns-2 and chip-accurate MATLAB simulations.

Congestion control algorithms seek to optimally utilize network resources by allocating a certain rate for each user. However, malicious clients can disregard the congestion control algorithms implemented at the clients and induce congestion at bottleneck links. Thus, in an adversarial environment, the network must enforce the congestion control algorithm in order to attain the optimal network utilization offered by the algorithm. Prior work protects only a single link incident on the enforcement routers neglecting damage inflicted upon other downstream links. We present CRAFT, a capability-based scheme to secure all downstream links of a deploying router. Our goal is to enforce a network-wide congestion control algorithm on all flows. As a reference design, we develop techniques to enforce the TCP congestion control. Our design regulates all flows to share bandwidth resources in a TCP-fair manner by emulating the TCP state machine in a CRAFT router. As a result, once a flow passes a single CRAFT router, it is TCP-fair on all downstream links of that router.

In this paper we present fundamental results on secure clock synchronization and man-in-the-middle detection using only timing information. Under the assumption of afflne clocks, we present a clock synchronization protocol that can operate on any channel on which data can be sent. We present a clock synchronization protocol from the literature and add verification steps on top of this protocol. These verification steps force man- in-the-middle attackers, who want to delay traffic between the endpoints and yet remain undetected, to impose only constant delays on packets. In a special case, we show that it is possible to identify and ignore attacker-delayed packets. We then show three different types of attackers: a half-duplex attacker that can always be caught using timing information alone, a double full-duplex attacker that can never be caught using only timing information, and a full-duplex attacker whose capability to perform man-in-the- middle attacks depends on its location relative to the endpoints and on the turnaround times of the endpoints. In particular, we prove that certain attackers are impossible to detect using only timing, and we construct defensive protocols that prevent all other man-in- the-middle delay attacks. A particularly noteworthy result is that a single attacker using the same radio technology as the endpoints can never successfully perform a man-in-the-middle attack to delay traffic. These results form a lightweight man-in-the-middle attack detection protocol, on top of which a wide variety of protocols can be built, including routing protocols and more sophisticated heavyweight protocols.

Due to the widespread adoption of the Global Positioning System (GPS), many systems have been designed to use the location information of participants. When these systems confer rights (such as access rights) based on location, such claim must be securely verified in order to prevent attackers from gaining access to resources that should be restricted. Substantial effort has been made on secure location verification; however, previous work does not address the impact of collusion attacks where adversaries share their private keys nor do they address a possible jamming attack where attackers inject a high amount of noise to prevent successful challenge and response receptions. In this paper, we propose a secure multilateration scheme that provides maximal security achievable by any time-of-flight based system that does not employ other verification methods.

Wireless communications are inherently symmetric; that is, it takes an attacker the same amount of power to modulate a signal as it does for a legitimate node to modulate the same signal. As a result, wireless communications are often susceptible to the jamming attack in which the attacker injects a high level of noise into the system. Spread spectrum has long been used to resist jamming attacks in unicast environments, or when the jammer has less information than the other receivers. Recently, we proposed a scheme for broadcast jamming mitigation based on spread spectrum and a binary key tree and showed some improvements over a multiple-unicast system. In this paper, we extend our previous work in five ways. First, we provide a theoretical result that under our scheme, jammers can cause only a limited number of losses. Second, we develop a dynamic tree-remerging scheme that achieves higher power efficiency than previously proposed schemes, and scales to an arbitrary number of receivers without increasing the number of codes in use; in particular, we send each transmission on at most 2j + 1 codes, where j is the number of jammers. Third, we show that our scheme is close to optimal, demonstrating that under certain realistic restrictions, the system cannot escape jamming without using at least j +1 codes. Fourth, we provide a detailed analysis of false alarm rates, showing both experimental and theoretical results. Finally, we perform a more extensive analysis of our system using both a chip-accurate MATLAB simulation and a bit-accurate event-driven simulation in the ns-2 network simulator; these simulations demonstrate that our scheme approaches the best possible performance.

Mobile communication systems are often susceptible to high level of noise injected by adversaries, known as jamming attack. Jamming is difficult to prevent in broadcast networks because a user that can decode a transmission can also jam the transmission. In this paper, we describe a code tree system that helps the physical layer circumvent jammers. This system works with any spread-spectrum communications system. In our system, the transmitter has more information than any single receiver. Each receiver cooperates with the transmitter to detect any jamming that affects that receiver. Our scheme mitigates the jamming attack while allowing the transmitter to transmit on fewer codes than the number of users. We simulated our system in a theoretical setting using MATLAB. The result shows significant improvement over naively transmitting on a single shared code.