Browsing by Author "Ahmadi, Hadi"

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    Information Theoretic Security over Physical-Layer Channels
    (2012-12-12) Ahmadi, Hadi; Safavi-Naini, Reyhaneh Alsadat
    Wyner [96] proved that unconditionally secure communication over noisy channels is possible if the wiretapping channel is noisier than the main channel. The work has developed the following belief: Physical-channel characteristics are great resources to build security functionalities in the information-theoretic framework. We follow this belief and investigate the three problems of secret key establishment, manipulation detection, and distance bounding verification over physical-layer channels. We investigate secret key establishment (SKE) between Alice and Bob when they are connected through a pair of noisy wiretap channels with leakage to Eve. Our results show the possibility of SKE even in cases where the main channels are noisier than Eve's channels. We then notice two implicit assumptions of this work: (i) local randomness is freely available, and (ii) the wiretap channels are independent. We remove Assumption (i) by considering no local randomness for the parties. The results appreciate the role of noise as a single resource for randomness derivation and key generation in this setting. Regarding the second assumption, we consider the general two-way wiretap channel, where simultaneous data transmission can help achieve higher key rates. We show under what condition our security requirements can be strengthened without sacrificing the SK capacity. We consider manipulation detection against physical-layer adversaries noticing their limitations. We define leakage-resilient algebraic manipulation detection (LR-AMD) codes and prove optimal LR-AMD code constructions in general and special leakage scenarios. We show two applications of these codes: (i) robust nonperfect secret sharing and (ii) manipulation detection over wiretap channels. We then discuss how these codes can be composed with other primitives to guarantee bitwise manipulation detection and SKE against active adversaries over binary wiretap channels. Distance bounding verification (DBV) allows a verifier to check an upper bound on a claimed distance from a prover. We study DBV over physical channels with security against distance fraud (DFA), ma a fraud (MFA) and terrorist fraud (TFA) attacks. We show efficient DFA- and MFA-secure protocols only using physical channel properties. We further prove that TFA-security becomes feasible if the parties' communication is limited by the bounded retrieval model (BRM).
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    Secret Key Agreement over Two-Way Broadcast Channels
    (2009-11-19T17:46:24Z) Ahmadi, Hadi; Safavi-Naini, Rei
    Wyner, and later Csisz´ar-and-K¨orner, studied the problem of secure communication over noisy channels. They proved that positive rates for one-way secure communication are achievable provided that the eavesdropper’s channel is noisier than the main channel. This paper considers the problem of information-theoretically secure key agreement when Alice and Bob are connected by a two-way noisy broadcast channel: that is, each party has access to a noisy broadcast channel that they can use for sending messages. We define secrecy capacity (for key agreement) of twoway broadcast channels and obtain a lower bound by presenting three key agreement protocols. In the first two protocols the key is effectively determined by one of the parties and securely delivered over the noisy channels. The third protocol, however, uses a novel interactive channel coding technique that results in a shared key which is a noisy version of the initiator’s message. We apply our results to the case that the noisy channels are binary symmetric and derive expressions for the secrecy capacities of the three protocols. We show that by using interactive coding, in some cases, it is possible to establish a secure key even if the main channel is 10 times noisier than the eavesdropper’s channels. Our results have theoretical and practical significance. We discuss our results and future work.