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Wireless One-time PAD : A Practical Method to Achieve Perfect Secrecy

Seyedehsan Bateni

Published May 11, 2018• 1 citation
OpenAlex

Abstract

In this thesis, a new practical method to realize one-time pad perfect secrecy for wireless \ncommunication is presented. Most commonly used security methods are based on cryp- tographic \ntechniques employed at the upper layers of a wireless network. These methods basically rely on the \ncomputational hardness of some mathematical problems. This com- putational complexity is vulnerable \nin nature due to fast-growing computational power of hardware technology, yet not taking into \naccount the revolution of Quantum computing in further future. Another core problematic issue \nexists in symmetric security systems; there is a deadlock between securing the channel and \nestablishing the shared key. We need the key for securing the channel, on the other hand, for \nsharing the key we need a secure channel. \n \nTo address such vulnerabilities, Physical Layer Security (PLS) has been widely studied in recent \nyears. PLS schemes build on the idea of turning unpredictable and random wire- less channel \ncharacteristics into a source for information-theoretic security. Information- theoretic security \nitself, relies on Shannon’s pioneer work . Shannon, inspired by one-time pad, also known as Vernam \ncipher, theoretically showed that the only unconditional per- fect secrecy system is a one-time pad \nwith a key at least as random as the plaintext, i.e., a system that uses a different random key to \ncipher any new plaintext. In PLS key genera- tion methods, legitimate parties alternately send \nprobe signals and estimate Channel State Information (CSI) of common random channel and then \nconvert enough amount of these estimates to secure shared keys. To achieve perfect secrecy, the key \ngeneration methods must meet the key randomness and Key Generation Rate (KGR) requirements of \ntheir specific cryptographic applications. \n \nIn this research a new practical system for achieving unconditional perfect secrecy is presented. \nOur system uses channel phase as the probing parameter to fully benefit from its uniform \ndistribution over [0, 2π]. It also uses an encryption method based on modulo- \n2π addition of phase values which is the perfect counterpart of XOR addition in binary one-time \npad. Moreover, by intentionally perturbing the wireless channel in vicinity of the transceiver \nantenna based on RF-mirrors structure, it produces different random phase values in each channel \nprobing, much faster than the inherent channel variation would do, resulting in dramatically higher \nKGR than any wide-band PLS scheme presented so far and realizing true perfect secrecy. Most \nimportantly, the focus of this research is a detailed practical algorithm for implementing the \nsystem as well as empirical results which makes \nour system the first channel-phase-based PLS scheme implementation, reported so far.

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The current research on physical layer security is far from implementations in practical networks, arguably due to impractical assumptions in the literature and the limited applicability of physical layer security. Aiming to reduce the gap between theory and practice, this thesis focuses on wireless physical layer security towards practical assumptions and requirements. In the first half of the thesis, we reduce the dependence of physical layer security on impractical assumptions. The secrecy enhancements and analysis based on impractical assumptions cannot lead to any true guarantee of secrecy in practical networks. The current study of physical layer security was often based on the idealized assumption of perfect channel knowledge on both legitimate users and eavesdroppers. We study the impact of channel estimation errors on secure transmission designs. We investigate the practical scenarios where both the transmitter and the receiver have imperfect channel state information (CSI). Our results show how the optimal transmission design and the achievable throughput vary with the amount of knowledge on the eavesdropper's channel. Apart from the assumption of perfect CSI, the analysis of physical layer security often ideally assumed the number of eavesdropper antennas to be known. We develop an innovative approach to study secure communication systems without knowing the number of eavesdropper antennas by introducing the concept of spatial constraint into physical layer security. That is, the eavesdropper is assumed to have a limited spatial region to place (possibly an infinite number of) antennas. We show that a non-zero secrecy rate is achievable with the help of a friendly jammer, even if the eavesdropper places an infinite number of antennas in its spatial region. In the second half of the thesis, we improve the applicability of physical layer security. The current physical layer security techniques to achieve confidential broadcasting were limited to application in single-cell systems. The primary challenge to achieve confidential broadcasting in the multi-cell network is to deal with not only the inter-cell but also the intra-cell information leakage and interference. To tackle this challenge, we design linear precoders performing confidential broadcasting in multi-cell networks. We optimize the precoder designs to maximize the secrecy sum rate with based on the large-system analysis. Finally, we improve the applicability of physical layer security from a fundamental aspect. The analysis of physical layer security based on the existing secrecy metric was often not applicable in practical networks. We propose new metrics for evaluating the secrecy of transmissions over fading channels to address the practical limitations of using existing secrecy metrics for such evaluations. The first metric establishes a link between the concept of secrecy outage and the eavesdropper's ability to decode confidential messages. The second metric provides an error-probability-based secrecy metric which is often used for the practical implementation of secure wireless systems. The third metric characterizes how much or how fast the confidential information is leaked to the eavesdropper. We show that the proposed secrecy metrics enable one to appropriately design secure communication systems with different views on how secrecy is measured.

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arXiv:1901.05324•Journal of Information Security and Cryptography (Enigma)•Jan 27, 2019•0 citations
In this thesis, a new practical method to realize one-time pad perfect secrecy for wireless \ncommunication is presented. Most commonly used security methods are based on cryp- tographic \ntechniques employed at the upper layers of a wireless network. These methods basically rely on the \ncomputational hardness of some mathematical problems. This com- putational complexity is vulnerable \nin nature due to fast-growing computational power of hardware technology, yet not taking into \naccount the revolution of Quantum computing in further future. Another core problematic issue \nexists in symmetric security systems; there is a deadlock between securing the channel and \nestablishing the shared key. We need the key for securing the channel, on the other hand, for \nsharing the key we need a secure channel. \n \nTo address such vulnerabilities, Physical Layer Security (PLS) has been widely studied in recent \nyears. PLS schemes build on the idea of turning unpredictable and random wire- less channel \ncharacteristics into a source for information-theoretic security. Information- theoretic security \nitself, relies on Shannon’s pioneer work . Shannon, inspired by one-time pad, also known as Vernam \ncipher, theoretically showed that the only unconditional per- fect secrecy system is a one-time pad \nwith a key at least as random as the plaintext, i.e., a system that uses a different random key to \ncipher any new plaintext. In PLS key genera- tion methods, legitimate parties alternately send \nprobe signals and estimate Channel State Information (CSI) of common random channel and then \nconvert enough amount of these estimates to secure shared keys. To achieve perfect secrecy, the key \ngeneration methods must meet the key randomness and Key Generation Rate (KGR) requirements of \ntheir specific cryptographic applications. \n \nIn this research a new practical system for achieving unconditional perfect secrecy is presented. \nOur system uses channel phase as the probing parameter to fully benefit from its uniform \ndistribution over [0, 2π]. It also uses an encryption method based on modulo- \n2π addition of phase values which is the perfect counterpart of XOR addition in binary one-time \npad. Moreover, by intentionally perturbing the wireless channel in vicinity of the transceiver \nantenna based on RF-mirrors structure, it produces different random phase values in each channel \nprobing, much faster than the inherent channel variation would do, resulting in dramatically higher \nKGR than any wide-band PLS scheme presented so far and realizing true perfect secrecy. Most \nimportantly, the focus of this research is a detailed practical algorithm for implementing the \nsystem as well as empirical results which makes \nour system the first channel-phase-based PLS scheme implementation, reported so far.
The one-time pad (OTP) secure transmission relies on the random keys to achieve perfect secrecy, while the unpredictable wireless channel is shown to be a good random source. There is very few work of the joint design of OTP and key generation from wireless channels. This article provides a comprehensive and quantitative investigation on secure transmission achieved by OTP and wireless channel randomness. We propose two OTP secure transmission schemes, i.e., identical key-based physical-layer secure transmission (IK-PST) and un-IK-PST (UK-PST). We quantitatively analyze the performance of both schemes and prove that UK-PST outperforms IK-PST. We extend the pairwise schemes to a group of users in networks with star and chain topologies. We implement prototypes of both schemes and evaluate the proposed schemes through both simulations and experiments. The results verify that UK-PST has a higher effective secret transmission rate than that of IK-PST for scenarios with both pairwise and group users.
The current research on physical layer security is far from implementations in practical networks, arguably due to impractical assumptions in the literature and the limited applicability of physical layer security. Aiming to reduce the gap between theory and practice, this thesis focuses on wireless physical layer security towards practical assumptions and requirements. In the first half of the thesis, we reduce the dependence of physical layer security on impractical assumptions. The secrecy enhancements and analysis based on impractical assumptions cannot lead to any true guarantee of secrecy in practical networks. The current study of physical layer security was often based on the idealized assumption of perfect channel knowledge on both legitimate users and eavesdroppers. We study the impact of channel estimation errors on secure transmission designs. We investigate the practical scenarios where both the transmitter and the receiver have imperfect channel state information (CSI). Our results show how the optimal transmission design and the achievable throughput vary with the amount of knowledge on the eavesdropper's channel. Apart from the assumption of perfect CSI, the analysis of physical layer security often ideally assumed the number of eavesdropper antennas to be known. We develop an innovative approach to study secure communication systems without knowing the number of eavesdropper antennas by introducing the concept of spatial constraint into physical layer security. That is, the eavesdropper is assumed to have a limited spatial region to place (possibly an infinite number of) antennas. We show that a non-zero secrecy rate is achievable with the help of a friendly jammer, even if the eavesdropper places an infinite number of antennas in its spatial region. In the second half of the thesis, we improve the applicability of physical layer security. The current physical layer security techniques to achieve confidential broadcasting were limited to application in single-cell systems. The primary challenge to achieve confidential broadcasting in the multi-cell network is to deal with not only the inter-cell but also the intra-cell information leakage and interference. To tackle this challenge, we design linear precoders performing confidential broadcasting in multi-cell networks. We optimize the precoder designs to maximize the secrecy sum rate with based on the large-system analysis. Finally, we improve the applicability of physical layer security from a fundamental aspect. The analysis of physical layer security based on the existing secrecy metric was often not applicable in practical networks. We propose new metrics for evaluating the secrecy of transmissions over fading channels to address the practical limitations of using existing secrecy metrics for such evaluations. The first metric establishes a link between the concept of secrecy outage and the eavesdropper's ability to decode confidential messages. The second metric provides an error-probability-based secrecy metric which is often used for the practical implementation of secure wireless systems. The third metric characterizes how much or how fast the confidential information is leaked to the eavesdropper. We show that the proposed secrecy metrics enable one to appropriately design secure communication systems with different views on how secrecy is measured.
Due to the broadcast nature of wireless channels, wireless communication is vulnerable to eavesdropping, message modification, and node impersonation. Securing the wireless communication requires the shared secret keys between the communicating entities. Traditional security schemes rely on public key infrastructures and cryptographic algorithms to manage secret keys. Recently, many physical-layer-based methods have been proposed as alternative solutions for key generation in wireless networks. These methods exploit the inherent randomness of the wireless fading channel to generate secret keys while providing information-theoretical security without intensive cryptographic computations. This article provides an overview of the existing PHY-based key generation schemes exploiting the randomness of the wireless channels. Specifically, we first introduce the fundamental and general framework of the PHY-based key generation schemes and then categorize them into two classes: received-signal-strength-based and channel- phase-based protocols. Finally, we present a performance comparison of them in terms of key disagreement probability, key generation rate, key bit randomness, scalability, and implementation issues.
Physical layer security (PLS) is a new paradigm aiming at securing communications between legitimate parties at the physical layer. Conventionally, achieving confidentiality in communication networks relies on cryptographic techniques such as public-key cryptography, secret-key distribution and symmetric encryption. Such techniques are deemed secure based on the assumption of limited computational abilities of a wiretapper. Given the relentless progress in computational capacities and the dynamic topology and proliferation of modern wireless networks, the relevance of the previous techniques in securing communications is more and more questionable and less and less reliable. In contrast to this paradigm, PLS does not assume a specific computational power at any eavesdropper, its premise to guarantee provable security via employing channel coding techniques at the physical layer exploiting the inherent randomness in most communication systems. In this dissertation, we investigate a particular aspect of PLS, which is secret-key agreement, also known as secret-sharing. In this setup, two legitimate parties try to distill a secret-key via the observation of correlated signals through a noisy wireless channel, in the presence of an eavesdropper who must be kept ignorant of the secret-key. Additionally, a noiseless public channel is made available to the legitimate parties to exchange public messages that are also accessible to the eavesdropper. Recall that key agreement is an important aspect toward realizing secure communications in the sense that the key can be used in a one-time pad scheme to send the confidential message. In the first part, our focus is on secret-sharing over Rayleigh fading quasi-static channels. We study the fundamental relationship relating the probability of error and a given target secret-key rate in the high power regime. This is characterized through the diversity multiplexing tradeoff (DMT) concept, that we define for our model and then characterize it. We show that the impact of the secrecy constraint is to reduce the effective number of transmit antennas by the number of antennas at the eavesdropper. Toward this characterization, we provide several schemes achieving the DMT and we highlight disparities between coding for the wiretap channel and coding for secret-key agreement. In the second part of the present work, we consider a fast-fading setting in which the wireless channels change during each channel use. We consider a correlated environment where transmit, legitimate receiver and eavesdropper antennas are correlated. We characterize the optimal strategy achieving the highest secret-key rate. We also identify the impact of correlation matrices and illustrate our analysis with various numerical results. Finally, we study the system from an energy-efficiency point of view and evaluate relevant metrics as the minimum energy required for sharing a secret-key bit and the wideband slope.
The Non-Reconciled Keys-based One-Time Pad (NRK-OTP) secure transmission scheme has attracted widespread attention since it reduces communication cost and computational complexity caused by information reconciliation. However, this scheme utilizes quantization to convert the analog channel estimates into binary sequences, which results in channel estimation errors being amplified. To address the problem, this letter proposes a Non-Quantization Keys-based One-Time Pad (NQK-OTP) secure transmission scheme. First, the uniformly distributed keys are generated from the wireless channel without quantization. Novel encryption and decryption algorithms are then presented to encrypt and decrypt modulated signals via OTP. Analytical and simulation results demonstrate that the proposed scheme can realize perfect secrecy and defend against symbol detection attacks. Compared with the NRK-OTP secure transmission scheme, the proposed scheme can achieve significant performance improvement in terms of Bit Error Rate (BER).
Among the problems to guarantee secrecy for in-transit information, the difficulties involved in renewing cryptographic keys in a secure way using couriers, the perfect secrecy encryption method known as One-Time-Pad (OTP) became almost obsolete. Pure quantum key distribution (QKD) ideally offers security for key distribution and could revive OTP. However, special networks that may need optical fibers, satellite, relay stations, expensive detection equipment compared with telecom technology and the slow protocol offer powerful obstacles for widespread use of QKD. Classical encryption methods flood the secure communication landscape. Many of them rely its security on historical difficulties such as factoring of large numbers - their alleged security sometimes are presented as the difficulty to brake encryption by brute force. The possibility for a mathematical breakthrough that could make factoring trivial are poorly discussed. This work proposes a solution to bring perfect secrecy to in-transit communication and without the above problems. It shows the key distribution scheme (nicknamed KeyBITS Platform) based on classical signals carrying information but that carry with them recordings of quantum noise. Legitimate users start with a shared information of the coding bases used that gives them an information advantage that allows easy signal recovery. The recorded noise protects the legitimate users and block the attacker's access. This shared information is refreshed at the end of each batch of keys sent providing the secret shared information for the next round. With encryption keys distilled from securely transmitted signals at each round OTP can be revived and at fast speeds.