We propose a systematic concatenated coding scheme based on the combination of interleaving with powerful channel codes and jamming for wireless secrecy under the practical assumption of codes in the finite blocklength regime. The basic idea lies in generating a short random key that is used to shuffle/interleave information at the source, Alice. This key is then sent to the legitimate receiver, Bob, during a brief period of advantageous communication over the eavesdropper Eve (e.g., due to more interference from a jammer). Finally, the key is decoded at Bob to properly deinterleave the original information. Bob receives a better quality version of the interleaving key, therefore having the needed advantage over Eve. Information reliability is provided by a strong inner code, while security against Eve results from the proper selection of the outer code and interference levels over the key. We propose a methodology for selection of the outer code with reliability and security constraints. For that, we introduce bit error complementary cumulative distribution function metrics, suitable for security and reliability analysis of error correcting codes.
We propose a systematic concatenated coding scheme based on the combination of interleaving with powerful channel codes and jamming for wireless secrecy under the practical assumption of codes in the finite blocklength regime. The basic idea lies in generating a short random key that is used to shuffle/interleave information at the source, Alice. This key is then sent to the legitimate receiver, Bob, during a brief period of advantageous communication over the eavesdropper Eve (e.g., due to more interference from a jammer). Finally, the key is decoded at Bob to properly deinterleave the original information. Bob receives a better quality version of the interleaving key, therefore having the needed advantage over Eve. Information reliability is provided by a strong inner code, while security against Eve results from the proper selection of the outer code and interference levels over the key. We propose a methodology for selection of the outer code with reliability and security constraints. For that, we introduce bit error complementary cumulative distribution function metrics, suitable for security and reliability analysis of error correcting codes.
This paper presents a practical physical-layer security scheme based on coding methodologies combined with self-jamming to combat advantaged eavesdroppers, i.e., eavesdroppers that may possess an equal or even better channel than the legitimate receiver. We introduce a strengthened security gap notion, where reliability is assured by typical bit-error rate (BER) measurements, but secrecy is guaranteed by considering the entire distribution of messages upon reception, instead of average measures. Relying on this new security gap notion, we then propose a scheme that combines concatenated coding with self-jamming by the legitimate receiver for effective security and reliability even when eavesdroppers possess a channel with equal or better conditions than the legitimate receiver.
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.
In this work, we consider the pros and cons of using various layers of keyless coding to achieve secure and reliable communication over the Gaussian wiretap channel. We define a new approach to information theoretic security, called practical secrecy and the secrecy benefit, to be used over real-world channels and finite blocklength instantiations of coding layers, and use this new approach to show the fundamental reliability and security implications of several coding mechanisms that have traditionally been used for physical-layer security. We perform a systematic/structured analysis of the effect of error-control coding, scrambling, interleaving, and coset coding, as coding layers of a secrecy system. Using this new approach, scrambling and interleaving are shown to be of no effect in increasing information theoretic security, even when measuring the effect at the output of the eavesdropper's decoder. Error control coding is shown to present a trade-off between secrecy and reliability that is dictated by the chosen code and the signal-to-noise ratios at the legitimate and eavesdropping receivers. Finally, the benefits of secrecy coding are highlighted, and it is shown how one can shape the secrecy benefit according to system specifications using combinations of different layers of coding to achieve both reliable and secure throughput.
We propose a coding methodology for physical layer security with adaptive characteristics, whereby adaptive we mean that the system must be tunable to different operational points/signal-to-noise ratio levels of both the legitimate receiver and the eavesdropper. Based on interleaving and scrambling as techniques that shuffle the original message before transmission, we consider puncturing over an interleaving/scrambling key and/or over the message as a mechanism to provide the required adaptability to channel conditions. The proposed techniques have shown suitable adaptability to different channel quality levels of the legitimate receiver and eavesdropper, while still guaranteeing the desired reliability for the legitimate receiver and secrecy against the eavesdropper.
Wireless systems are susceptible to eavesdropping as an unwelcome result of the broadcast nature of the wireless medium. Fortunately, the wireless medium also provides endowments including the temporal dispersion, the capability of signal superposition and other properties, to facilitate defending against eavesdropping. The focus of the thesis is to provide schemes for utilizing these properties at the physical layer and their performance analysis from an information-theoretic secrecy perspective. The work is based on Wyner's results on the wire-tap channel, in which the transmission between two legitimate users (Alice and Bob) is eavesdropped upon by Eve. The secrecy level is measured by the equivocation rate at Eve. The system performance is measured by the secrecy capacity. This is the maximum rate at which a message can be sent from Alice to Bob, while constraining the equivocation rate at Eve equal to the communication rate, and thus ensuring that Eve cannot deduce any useful information asymptotically. First, the scenario where a secret message needs to be delivered to the intended receiver within a given delay constraint and without the knowledge of the channel state information (CSI) at the transmitter is considered. In particular, hybrid automatic retransmission request (HARQ) protocols are revisited for a block-fading wire-tap channel via a joint consideration of channel coding, secrecy coding, and retransmission protocols. Two secure HARQ protocols: a repetition time diversity (RTD) scheme with maximal-ratio combining, and an incremental redundancy (INR) scheme based on ratecompatible Wyner secrecy codes are analyzed via an outage-based formulation. The throughput of RTD and INR protocols under probabilistic outage requirements is derived. Asymptotic analysis and numerical computations are given to demonstrate both the benefits of HARQ protocols and the tradeoff between reliability and confidentiality in delay-constrained communications. Second, the effects of interference on information-theoretic secret communication is considered. More specifically, the wiretap channel with a helping interferer (WT-HI) is proposed and studied. Here, an interferer, which does not know the confidential message, helps in ensuring the secrecy of the message by sending independent signals. Achievable secrecy rates and upper bounds on the secrecy capacity are given for both discrete memoryless and Gaussian channels. Interference has conventionally been regarded as a harmful phenomenon that leads to decreasing the rate and the reliability performance of wireless systems. In this work, it is shown that interference can be exploited to assist wireless secrecy. Lastly, the problem of secret key generation over fading channels, in which there exists an additional authenticated, public and error-free feedback channel from Bob to Alice, is considered. A key generation scheme consisting of a communication phase and a key-generation phase is presented. The communication phase is based on layered broadcast coding, which adapts the decoded rate at Bob to the actual channel state without requiring CSI available at Alice. The key-generation phase is based on the messages decoded by Bob after the communication phase and the public feedback. The achievable secrecy key rate and the optimal power distribution over coded layers for maximizing the secrecy key rate are characterized. Theoretical and numerical results show that the broadcast approach outperforms the single-level-coding based approach significantly, and hence demonstrate the role of introducing self-interference in facilitating secret-key generation over slowly fading channels when transmit CSI is not available.
This paper presents a testbed implementation and evaluation of coding for secrecy schemes in a real environment through software defined radio platforms. These coding schemes rely on interleaving and scrambling with randomly generated keys to shuffle information before transmission. These keys are then encoded jointly with data and then hidden (erased) before transmission, thus only being retrievable through parity information resulting from encoded data. An advantage of the legitimate receiver (e.g. a better signal-to-noise ratio) on the reception of those keys provides the means to achieve secrecy against an adversary eavesdropper. Through this testbed implementation, we show the practical feasibility of coding for secrecy schemes in real-world environments, unveiling the usefulness of interleaving and scrambling with a hidden key to reduce the required advantage over an eavesdropper. We further describe and present solutions to a set of issues that appear when doing practical implementations of security schemes in software defined radio platforms.