Physical layer security can provide alternative means for securing the exchange of confidential messages in wireless applications. In this paper, the resilience of wireless multiuser networks to passive (interception of the broadcast channel) and active (interception of the broadcast channel and false feedback) eavesdroppers is investigated under Rayleigh fading conditions. Stochastic characterizations of the secrecy capacity (SC) are obtained in scenarios involving a base station and several destinations. The expected values and variances of the SC along with the probabilities of secrecy outages are evaluated in the following cases: (i) in the presence of passive eavesdroppers without any side information; (ii) in the presence of passive eavesdroppers with side information about the number of eavesdroppers; and (iii) in the presence of a single active eavesdropper with side information about the behavior of the eavesdropper. This investigation demonstrates that substantial secrecy rates are attainable on average in the presence of passive eavesdroppers as long as minimal side information is available. On the other hand, it is further found that active eavesdroppers can potentially compromise such networks unless statistical inference is employed to restrict their ability to attack. Interestingly, in the high signal to noise ratio regime, multiuser networks become insensitive to the activeness or passiveness of the attack.
Physical layer security can provide alternative means for securing the exchange of confidential messages in wireless applications. In this paper, the resilience of wireless multiuser networks to passive (interception of the broadcast channel) and active (interception of the broadcast channel and false feedback) eavesdroppers is investigated under Rayleigh fading conditions. Stochastic characterizations of the secrecy capacity (SC) are obtained in scenarios involving a base station and several destinations. The expected values and variances of the SC along with the probabilities of secrecy outages are evaluated in the following cases: (i) in the presence of passive eavesdroppers without any side information; (ii) in the presence of passive eavesdroppers with side information about the number of eavesdroppers; and (iii) in the presence of a single active eavesdropper with side information about the behavior of the eavesdropper. This investigation demonstrates that substantial secrecy rates are attainable on average in the presence of passive eavesdroppers as long as minimal side information is available. On the other hand, it is further found that active eavesdroppers can potentially compromise such networks unless statistical inference is employed to restrict their ability to attack. Interestingly, in the high signal to noise ratio regime, multiuser networks become insensitive to the activeness or passiveness of the attack.
Security is becoming an increasingly important issue in wireless communications, to which physical layer approaches can contribute by providing addition resources for securing confidential messages. In this paper, the resilience of multi-user networks to passive and active eavesdropping is investigated. In particular, average secrecy capacities are evaluated in scenarios involving a base station and several terminals, some of which constitute passive or active eavesdroppers. Network resources (e.g. power) are allocated by the base station based on the available channel state information. The average secrecy capacity of such a network is evaluated in the following cases: (i) in the presence of passive eavesdroppers when no side information is available to the base station; (ii) in the presence of passive eavesdroppers with side information available; and (iii) in the presence of a single active eavesdropper with side information available. This investigation demonstrates that substantial secrecy rates are attainable in the presence of passive eavesdroppers as long as minimal side information, e.g. a statistical characterization of the number of potential eavesdroppers, is available to the base station. On the other hand, it is further found that active eavesdroppers can potentially compromise such networks unless statistical inference is employed to restrict their ability to attack.
The resilience of block fading wireless orthogonal frequency division multiple access (OFDMA) networks to passive eavesdroppers is investigated. The network secrecy capacity is evaluated in scenarios involving a base station and several terminals, some of which constitute passive eavesdroppers. Assuming a block fading Rayleigh channel, the probability of a secrecy outage during a transmission frame is evaluated with respect to a target secrecy rate τ in the following cases: (i) in the absence of any cooperation between the network nodes, and, (ii) when the full multi-user diversity is exploited both by the legitimate users as well as by the eavesdroppers. Remarkably, it is demonstrated that in a network of as few as 12 legitimate users and a single eavesdropper it is possible to transmit 1 bit/sec/Hz with a probability of secrecy outage less than 1%. Furthermore, the delay constrained secrecy capacity of this network is evaluated when the full channel state information (CSI) is available both at the base station and at all receiving nodes. A secure waterfilling scheme is discussed, satisfying a short-term power constraint.
Information security has been a very important issue in wireless networks. With the ever-increasing amount of data being exchanged over wireless networks, the confidentiality of information needs to be protected from unauthorized users called eavesdropper. Due to the broadcast nature of the wireless medium, the transmissions between legitimate users maybe overheard and intercepted by the unauthorized parties, which makes wireless transmission vulnerable to potential eavesdropping attacks. The security of wireless communications plays an increasingly important role in the cybercrime defense against unauthorized activities. We consider the wireless physical layer security which has been explored for the sake of enhancing the protection of wireless communications against eavesdroppers. We consider the problem of secret communication through Rayleigh fading channel in the presence of an eavesdropper in which the transmitter knows the channel state information of both the main and eavesdropper channel. Then, we analyze the average capacity of the main channel and eavesdropper channel from which an expression of secrecy capacity is derived based on the cumulative distribution function and probability density function of the signal to noise ratio. We also analyze an expression for the symbol error rate of the main channel, and the outage probability is obtained for the main transmission. Finally, we perform the numerical results in MATLAB.
Multiuser multiple-input multiple-output (MIMO) wireless techniques have received tremendous attention as a way to achieve high spectral efficiency in current mobile communication systems such as Long Term Evolution (LTE) [1]. Due to the broadcast nature of the physical medium, wireless multiuser communications are very susceptible to eavesdropping, and it is critical to secure the transmitted information. In this work, consider the broadcast channel with confidential messages and external eavesdroppers (BCCE), where a multi-antenna base station [2] simultaneously communicates to multiple potentially malicious users, in the presence of randomly located external eavesdroppers. The secrecy capacity is measured in terms of outage probability and provides a complete characterization of the maximum transmission rate at which the eavesdropper is unable to decode any information. Using the proposed model, the secrecy rates is achieved with regularized channel inversion (RCI) precoding and analyzed by performing a large-system analysis where the number of users K and the number of transmit antennas N both grow to infinity in a fixed ratio. Finally an explicit expression for the probability of secrecy outage and the system performance is analyzed in the presence of both colluding and non-colluding eavesdroppers.
Wireless networks have experienced rapid evolutions toward sustainability, scalability and interoperability. The digital economy is driven by future networked societies to a more holistic community of intelligent infrastructures and connected services for a more sustainable and smarter society. Furthermore, an enormous amount of sensitive and confidential information, e.g., medical records, electronic media, financial data, and customer files, is transmitted via wireless channels. The implementation of higher layer key distribution and management was challenged by the emergence of these new advanced systems. In order to resist various malicious abuses and security attacks, physical layer security (PLS) has become an appealing alternative. The basic concept behind PLS is to exploit the characteristics of wireless channels for the confidentiality. Its target is to blind the eavesdroppers such that they cannot extract any confidential information from the received signals. This thesis presents solutions and analyses to improve the PLS in wireless networks. \n \nIn the second chapter, we investigate the secrecy capacity performance of an amplify-andforward (AF) dual-hop network for both distributed beamforming (DBF) and opportunistic relaying (OR) techniques. We derive the capacity scaling for two large sets; trustworthy relays and untrustworthy aggressive relays cooperating together with a wire-tapper aiming to intercept the message. We show that the capacity scaling in the DBF is lower bounded by a value which depends on the ratio between the number of the trustworthy and the untrustworthy aggressive relays, whereas the capacity scaling of OR is upper bounded by a value depending on the number of relays as well as the signal to noise ratio (SNR). \n \nIn the third chapter, we propose a new location-based multicasting technique, for dual phase AF large networks, aiming to improve the security in the presence of non-colluding passive eavesdroppers. We analytically demonstrate that the proposed technique increases the security by decreasing the probability of re-choosing a sector that has eavesdroppers, for each transmission time. Moreover, we also show that the secrecy capacity scaling of our technique is the same as for broadcasting. Hereafter, the lower and upper bounds of the secrecy outage probability are calculated, and it is shown that the security performance is remarkably enhanced, compared to the conventional multicasting technique. \n \nIn the fourth chapter, we propose a new cooperative protocol, for dual phase amplify-andforward large wireless sensor networks, aiming to improve the transmission security while taking into account the limited capabilities of the sensor nodes. In such a network, a portion of the K relays can be potential passive eavesdroppers. To reduce the impact of these untrustworthy relays on the network security, we propose a new transmission protocol, where the source agrees to share with the destination a given channel state information (CSI) of source-trusted relay-destination link to encode the message. Then, the source will use this CSI again to map the right message to a certain sector while transmitting fake messages to the other sectors. Adopting such a security protocol is promising because of the availability of a high number of cheap electronic sensors with limited computational capabilities. For the proposed scheme, we derived the secrecy outage probability (SOP) and demonstrated that the probability of receiving the right encoded information by an untrustworthy relay is inversely proportional to the number of sectors. We also show that the aggressive behavior of cooperating untrusted relays is not effective compared to the case where each untrusted relay is trying to intercept the transmitted message individually. \n \nFifth and last, we investigate the physical layer security performance over Rayleigh fading channels in the presence of impulsive noise, as encountered, for instance, in smart grid environments. For this scheme, secrecy performance metrics were considered with and without destination assisted jamming at the eavesdropper’s side. From the obtained results, it is verified that the SOP, without destination assisted jamming, is flooring at high signal-to-noise-ratio values and that it can be significantly improved with the use of jamming.
In this paper, the physical layer security of a multi-user jamming-assisted broadcast network in the presence of multiple eavesdroppers. Specifically, a base station (BS) is broadcasting data to multiple end-users via direct links in the presence of multiple passive wiretappers, while both the legitimate users and the eavesdroppers use a maximal-ratio combining scheme to achieve high spatial diversity gain. Furthermore, the BS is broadcasting a jamming signal that can not be canceled by the eavesdroppers to increase their decoding failure rates. All links are subject to Nakagami-m fading models. Relying on the upper incomplete moment-generating function of the combined Signal-to-interference-plus-noise ratio (SINR) at each wiretapper’s MRC output, tight approximate and asymptotic expressions for the secrecy outage probability (SOP) are derived considering two different scenarios, i.e., (i) absence and (ii) presence of the broadcasted artificial noise. The impact of the jamming signal level, severity fading parameter, and the number of MRC branches are examined, while the most influential parameter on the system’s security is retrieved. Numerical results and simulations reveal the accuracy of the obtained analytical expressions and gain more useful insights into the system’s secrecy.