George T. Amariucai

Half-Duplex Active Eavesdropping in Fast-Fading Channels: A Block-Markov Wyner Secrecy Encoding Scheme

In this paper, we study the problem of half-duplex active eavesdropping in fast-fading channels. The active eavesdropper is a more powerful adversary than the classical eavesdropper. It can choose between two functional modes: eavesdropping the transmission between the legitimate parties (Ex mode), and jamming it (Jx mode)-the active eavesdropper cannot function in full duplex mode. We consider a conservative scenario, when the active eavesdropper can choose its strategy based on the legitimate transmitter-receiver pairs strategy, and thus, the transmitter and legitimate receiver have to plan for the worst. We show that conventional physical-layer secrecy approaches perform poorly (if at all), and we introduce a novel encoding scheme, based on very limited and unsecured feedback-the Block-Markov Wyner encoding scheme-which outperforms any schemes currently available.

Delegation of computation with verification outsourcing: curious verifiers

In the Cloud Computing paradigm, a user often reduces financial, personnel, and computational burdens by outsourcing computation and other IT services to a professional service provider. However, to be able to assure the correctness of the result, the user still needs to perform the verification himself. Such verification may be tedious and expensive. Consequently, users are likely to outsource (again) the verification workload to a third party. Other scenarios such as auditing and arbitrating may also require the use of third-party verification. Outsourcing verification will introduce new security challenges. One such challenge is to protect the computational task and the results from the untrusted third party verifier. In this work, we address this problem by proposing an efficient verification outsourcing scheme. To our knowledge, this is the first solution to the verification outsourcing problem. We show that, without using expensive fully-homomorphic encryption, an honest-but-curious third party can help to verify the result of an outsourced computational task without having to learn either the computational task or the result thereof. We have implemented our design by combining a novel commitment protocol and an additive-homomorphic encryption in the argument system model. The total cost of the verification in our design is less than the verifiers cost in the state-of-the-art argument systems that rely only on standard cryptographic assumptions.

An automatic, time-based, secure pairing protocol for passive RFID

This paper introduces the Adopted-Pet (AP) protocol, an automatic (i.e. requiring no human interaction) secure pairing protocol, adequate for the pairing between a passive RFID tag and a reader. Most pairing protocols rely for their security on a certain advantage that the legitimate devices have over any malicious users. Such advantages include proximity (employing near-field communication) or secret keys that are either produced with the assistance of, or verified by, the legitimate user. The advantage exploited by our novel AP protocol is the amount of uninterrupted time spent by the two devices in the proximity (although not requiring near-field communication) of each-other. We discuss several implementation configurations, all based on pseudo-random bit generators, employing short-length LFSRs, and requiring no more than 2000 transistors. This makes the protocol ideally suited for low-cost passive RFID tags. For each configuration we show that the AP protocol is highly secure against occasional malicious entities.

Jamming games in fast-fading wireless channels

In this paper, we adopt outage probability (lambda-capacity) in fast fading channels as a pay-off function in a zero- sum game between a legitimate transceiver pair and an uncorrelated Gaussian jammer. The transmitter aims at minimizing the outage probability, while the jammer attempts to maximize the outage probability. We consider both peak (over each codeword) and average (over all codewords) power constraints. For peak power constraints, a transmission rate is either supported by the system, or if too large, causes the whole transmission to fail. By imposing average power constraints, large rates can be supported at the cost of positive probability of codeword error. Maxmin and minimax power control strategies are developed, which show that no Nash equilibrium of pure strategies exists under average power constraints.

Feedback-Based Collaborative Secrecy Encoding Over Binary Symmetric Channels

In this paper, we propose a feedback scheme for transmitting secret messages between two legitimate parties, over an eavesdropped communication link. Relative to Wyners traditional encoding scheme, our feedback-based encoding often yields larger rate-equivocation regions and achievable secrecy rates. More importantly, by exploiting the channel randomness inherent in the feedback channels, our scheme achieves a strictly positive secrecy rate even when the eavesdroppers channel is less noisy than the legitimate receivers channel. All channels are modeled as binary and symmetric. We demonstrate the versatility of our feedback-based encoding method by using it in three different configurations: the stand-alone configuration, the mixed configuration (when it combines with Wyners scheme), and the reversed configuration. Depending on the channel conditions, significant improvements over Wyners secrecy capacity can be observed in all configurations.

Mixed anti-jamming strategies in fixed-rate wireless systems over fast fading channels

We study the problem of jamming in a fixed-rate wireless system over fast fading channels. Both transmitter and jammer are subject to long term (average) power constraints. Our jamming problem is formulated as a zero-sum game, with the probability of outage as pay-off function and power control functions as strategies. We consider both the case with full channel state information (CSI) at all parties (available from a training and feedback protocol), and the case when no CSI is fed back from the receiver. Nash equilibria of mixed strategies are found by solving the generalized form of an older problem dated back to Bell and Cover [1].

Secret Common Randomness From Routing Metadata in Ad Hoc Networks

Establishing secret common randomness between two or multiple devices in a network resides at the root of communication security. In its most frequent form of key establishment, the problem is traditionally decomposed into a randomness generation stage (randomness purity is subject to employing often costly true random number generators) and an information-exchange agreement stage, which relies either on public-key infrastructure or on symmetric encryption (key wrapping). In this paper, we propose a secret-common-randomness establishment algorithm for ad hoc networks, which works by harvesting randomness directly from the network routing metadata, thus achieving both pure randomness generation and (implicitly) secret-key agreement. Our algorithm relies on the route discovery phase of an ad hoc network employing the dynamic source routing protocol, is lightweight, and requires relatively little communication overhead. The algorithm is evaluated for various network parameters in an OPNET ad hoc network simulator. Our results show that, in just 10 min, thousands of secret random bits can be generated network-wide, between different pairs in a network of 50 users.

Jamming Games in Fast-Fading Wireless Channels

In this paper, we adopt outage probability (lambda-capacity) in fast fading channels as a pay-off function in a zero- sum game between a legitimate transceiver pair and an uncorrelated Gaussian jammer. The transmitter aims at minimizing the outage probability, while the jammer attempts to maximize the outage probability. We consider both peak (over each codeword) and average (over all codewords) power constraints. For peak power constraints, a transmission rate is either supported by the system, or if too large, causes the whole transmission to fail. By imposing average power constraints, large rates can be supported at the cost of positive probability of codeword error. Maxmin and minimax power control strategies are developed, which show that no Nash equilibrium of pure strategies exists under average power constraints.

Extractable Common Randomness From Gaussian Trees: Topological and Algebraic Perspectives

In this paper, we study both topological and algebraic properties of unrooted Gaussian trees in order to characterize their security performance. Such performance is measured by the corresponding potential in extracting common randomness from a given tree, which is further determined by max-min and min-max conditional mutual information (CMI) values, subject to the order of selecting variables from the tree by legitimate nodes Alice and Bob, and an eavesdropper Eve, respectively. A new operation is proposed to transform a Gaussian tree into another, and also to order different Gaussian trees. Through such operation we construct several equivalent classes of Gaussian trees. Each class includes multiple Gaussian trees that can be partially ordered based on the associated max-min or min-max CMI metric, and thus, we can find the most secure and the least secure trees in each partially ordered set (poset). The union of all posets generates all possible non-isomorphic trees of the given number of variables. Then, we assign a particular polynomial to each Gaussian tree, and show that such polynomial can determine the relative security performance of the Gaussian tree with respect to other trees within the same class. In the end, based on a generalized integer partition method, we propose a novel approach to efficiently enumerate the most secure structures of all posets.

Evaluation of security robustness against information leakage in Gaussian polytree graphical models

Extensive works have been undertaken to develop efficient statistical inference algorithms based on graphical models. However, there still lacks sufficient understanding about how topological properties affect certain information related metrics for certain graphs. In this paper, we are particularly interested in finding out how topological properties of rooted polytrees for Gaussian random variables determine its security robustness, which is measured by our proposed max-min information (MaMI) metric. MaMI is defined as the maximin value of the conditional mutual information between any two random variables (nodes) in a given DAG, conditioned on the value of a third random variable, which is at full disposal of an eavesdropper, under a constraint of a given fixed joint entropy. We show some general topological properties which the desired max-min solutions satisfy. Under such properties, we prove the superior max-min feature of the linear topology for a simple but non-trivial case. The results not only help us understand the security strength of different rooted polytree type DAGs, which is critical when we evaluate the information leakage issues for various jointly Gaussian distributed measurements in networks, but also provide us another algebraic and analysis perspective in grasping some fundamental properties of such DAGs.