Secure communication over a wireless channel in the presence of a passive eavesdropper is considered. We present a method to exploit the eavesdropper's inherent receiver vulnerabilities to obtain everlasting secrecy. An ephemeral cryptographic key is pre-shared between the transmitter and the legitimate receiver and is utilized to induce intentional intersymbol interference (ISI). The legitimate receiver uses the key to cancel the ISI while the eavesdropper, since it does not have the key, cannot do such. It is shown that although ISI reduces the capacity of the main channel, it can lead to a net gain in secrecy rate. The achievable secrecy rates for different ISI filter settings are evaluated and the proposed method is compared with other information-theoretic security schemes.
Secure communication over a wireless channel in the presence of a passive eavesdropper is considered. We present a method to exploit the eavesdropper's inherent receiver vulnerabilities to obtain everlasting secrecy. An ephemeral cryptographic key is pre-shared between the transmitter and the legitimate receiver and is utilized to induce intentional intersymbol interference (ISI). The legitimate receiver uses the key to cancel the ISI while the eavesdropper, since it does not have the key, cannot do such. It is shown that although ISI reduces the capacity of the main channel, it can lead to a net gain in secrecy rate. The achievable secrecy rates for different ISI filter settings are evaluated and the proposed method is compared with other information-theoretic security schemes.
Secure communication over a wireless channel in the presence of a passive eavesdropper is considered. Our main interest is in the disadvantaged wireless environment, where the channel from the transmitter Alice to the eavesdropper Eve is (possibly much) better than that from Alice to Bob, hence making information-theoretic secrecy challenging. We present a method to exploit inherent vulnerabilities of the eavesdropper's receiver through the use of “cheap” cryptographically-secure key-bits, which only need be kept secret from Eve for the (short) transmission period of the message, to obtain information-theoretic (i.e. everlasting) secret bits at Bob. In particular, based on an ephemeral cryptographic key pre-shared between Alice and Bob, a random jamming signal with large variations is added to each symbol. The legitimate receiver Bob uses the key to subtract the jamming signal immediately, while Eve is forced to perform the inherently nonlinear operation of recording the signal; when Eve then obtains the key, which we assume pessimistically (for Alice) happens right after message transmission, Eve can then immediately subtract the jamming signal from the recorded signal. But, because of the intervening non-linear operation in Eve's receiver and the non-commutativity of nonlinear operations, Bob's channel and Eve's channel have different achievable rates and information-theoretic secrecy can be obtained, hence achieving the goal of converting the vulnerable cryptographic secret key into information-theoretic secure bits. The achievable secrecy rates for different settings are evaluated. Among other results, it is shown that, even when the eavesdropper has perfect access to the output of the transmitter (albeit through an imperfect analog-to-digital converter), the method can still achieve a positive secrecy rate.
Secure communication over a wiretap channel is considered in the disadvantaged wireless environment, where the eavesdropper channel is (possibly much) better than the main channel. We present a method to exploit inherent vulnerabilities of the eavesdroppers receiver to obtain everlasting secrecy. Based on an ephemeral cryptographic key pre-shared between the transmitter Alice and the intended recipient Bob, a random jamming signal is added to each symbol. Bob can subtract the jamming signal before recording the signal, while the eavesdropper Eve is forced to perform these non-commutative operations in the opposite order. Thus, information-theoretic secrecy can be obtained, hence achieving the goal of converting the vulnerable “cheap” cryptographic secret key bits into “valuable” information-theoretic (i.e., everlasting) secure bits. We evaluate the achievable secrecy rates for different settings, and show that, even when the eavesdropper has perfect access to the output of the transmitter (albeit through an imperfect analog-to-digital converter), the method can still achieve a positive secrecy rate. Next we consider a wideband system, where Alice and Bob perform frequency hopping in addition to adding the random jamming to the signal, and we show the utility of such an approach even in the face of substantial eavesdropper hardware capabilities.
The physical layer security problem with a passive eavesdropper is considered in this letter. We propose a method to obtain everlasting secrecy by exploiting inter-symbol interference (ISI) in eavesdropper. In the proposed method, the pulse shaping filter in the transmitter changes with time in the faster-than-Nyquist (FTN) signaling structure. The filter hopping pattern is pre-shared between the transmitter and the legitimate receiver. Knowing the hopping pattern, the legitimate receiver can mitigate the ISI as that in FTN. Otherwise, the eavesdropper will experience severe interference. The results show that even the eavesdropping link is much better than the legitimate link, a positive secrecy rate is also obtained. The secrecy rates for various examples of the proposed method are evaluated and the comparisons with other information-theoretic security schemes are also shown.
Secure communication over a memoryless wiretap channel in the presence of a passive eavesdropper is considered. Traditional information-theoretic security methods require an advantage for the main channel over the eavesdropper channel to achieve a positive secrecy rate, which in general cannot be guaranteed in wireless systems. Here, we exploit the non-linear conversion operation in the eavesdropper's receiver to obtain the desired advantage - even when the eavesdropper has perfect access to the transmitted signal at the input to their receiver. The basic idea is to employ an ephemeral cryptographic key to force the eavesdropper to conduct two operations, at least one of which is non-linear, in a different order than the desired recipient. Since non-linear operations are not necessarily commutative, the desired advantage can be obtained and information-theoretic secrecy achieved even if the eavesdropper is given the cryptographic key immediately upon transmission completion. In essence, the lack of knowledge of the key during the short transmission time inhibits the recording of the signal in such a way that the secret information can never be extracted from it. The achievable secrecy rates for different countermeasures that the eavesdropper might employ are evaluated. It is shown that even in the case of an eavesdropper with uniformly better conditions (channel and receiver quality) than the intended recipient, a positive secrecy rate can be achieved.
In this letter, we propose a novel scheme for enhancing the security of the information transfer between resource-limited devices. We select a pulse from a set of T-orthogonal pulses for shaping the data at source (S) based on legitimate channel state information (CSI). A destination (D) having the CSI, properly samples the output of the matched filter. An eavesdropper (E) having no knowledge of the legitimate CSI, may or may not sample correctly, thereby, inducing artificial intersymbol interference (ISI) at the E. We also consider a case where the S - E link is correlated with the S - D link (when E and D are closely located). We derive optimal thresholds at E, S for switching the selection of a pulse in maximizing and minimizing the achievable rate at E, respectively. We derive closed-form expressions for upper bound and lower bound on the secrecy outage probability (SOP) for the independent case. Simulation results show that unlike at D, the symbol error rate (SER) at E saturates at a high SER due to the induced ISI.
Information-theoretic security guarantees that a message is kept secret from potential eavesdroppers regardless of their current or future computational abilities. But current information-theoretic security approaches generally rely on an advantage of the channel of the desired recipient over the adversary, and such an advantage can be difficult to guarantee in a wireless network where an eavesdropper might be very near the transmitter. This paper initiates an approach to everlasting security for wireless communication links by exploiting a fundamental concept from systems theory: that nonlinear systems are not (necessarily) commutative. This property is exploited by employing a short-term cryptographic key to force the eavesdropper's signal to be subjected to nonlinear operations in the reverse order of that of the signal at the desired recipient. After introducing the idea and providing analysis for the general case, we next consider a simple (and practical) instantiation where the transmitter uses the ephemeral cryptographic key to rapidly power modulate the transmitted signal. Secrecy rates with this rapid power modulation under various assumptions establish the promise of the approach, even in the case of an eavesdropper with uniformly better conditions (channel and receiver quality) than the intended recipient.