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109
Secure communication over fading channels
, 2007
"... The fading broadcast channel with confidential messages (BCC) is investigated, where a source node has common information for two receivers (receivers 1 and 2), and has confidential information intended only for receiver 1. The confidential information needs to be kept as secret as possible from rec ..."
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Cited by 188 (21 self)
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The fading broadcast channel with confidential messages (BCC) is investigated, where a source node has common information for two receivers (receivers 1 and 2), and has confidential information intended only for receiver 1. The confidential information needs to be kept as secret as possible from receiver 2. The broadcast channel from the source node to receivers 1 and 2 is corrupted by multiplicative fading gain coefficients in addition to additive Gaussian noise terms. The channel state information (CSI) is assumed to be known at both the transmitter and the receivers. The parallel BCC with independent subchannels is first studied, which serves as an informationtheoretic model for the fading BCC. The secrecy capacity region of the parallel BCC is established. This result is then specialized to give the secrecy capacity region of the parallel BCC with degraded subchannels. The secrecy capacity region is then established for the parallel Gaussian BCC, and the optimal source power allocations that achieve the boundary of the secrecy capacity region are derived. In particular, the secrecy capacity region is established for the basic Gaussian BCC. The secrecy capacity results are then
Discrete memoryless interference and broadcast channels with confidential messages: secrecy rate regions
 IEEE Transactions on Information Theory
, 2008
"... Abstract — Discrete memoryless interference and broadcast channels in which independent confidential messages are sent to two receivers are considered. Confidential messages are transmitted to each receiver with perfect secrecy, as measured by the equivocation at the other receiver. In this paper, w ..."
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Cited by 161 (12 self)
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Abstract — Discrete memoryless interference and broadcast channels in which independent confidential messages are sent to two receivers are considered. Confidential messages are transmitted to each receiver with perfect secrecy, as measured by the equivocation at the other receiver. In this paper, we derive inner and outer bounds for the achievable rate regions for these two communication systems. I.
Wireless informationtheoretic security  part I: Theoretical aspects
 IEEE Trans. on Information Theory
, 2006
"... In this twopart paper, we consider the transmission of confidential data over wireless wiretap channels. The first part presents an informationtheoretic problem formulation in which two legitimate partners communicate over a quasistatic fading channel and an eavesdropper observes their transmissi ..."
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Cited by 155 (12 self)
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In this twopart paper, we consider the transmission of confidential data over wireless wiretap channels. The first part presents an informationtheoretic problem formulation in which two legitimate partners communicate over a quasistatic fading channel and an eavesdropper observes their transmissions through another independent quasistatic fading channel. We define the secrecy capacity in terms of outage probability and provide a complete characterization of the maximum transmission rate at which the eavesdropper is unable to decode any information. In sharp contrast with known results for Gaussian wiretap channels (without feedback), our contribution shows that in the presence of fading informationtheoretic security is achievable even when the eavesdropper has a better average signaltonoise ratio (SNR) than the legitimate receiver — fading thus turns out to be a friend and not a foe. The issue of imperfect channel state information is also addressed. Practical schemes for wireless informationtheoretic security are presented in Part II, which in some cases comes close to the secrecy capacity limits given in this paper.
The relayeavesdropper channel: Cooperation for secrecy
 IEEE Trans. on Inf. Theory
, 2006
"... This paper establishes the utility of user cooperation in facilitating secure wireless communications. In particular, the fourterminal relayeavesdropper channel is introduced and an outerbound on the optimal rateequivocation region is derived. Several cooperation strategies are then devised and ..."
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Cited by 153 (6 self)
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This paper establishes the utility of user cooperation in facilitating secure wireless communications. In particular, the fourterminal relayeavesdropper channel is introduced and an outerbound on the optimal rateequivocation region is derived. Several cooperation strategies are then devised and the corresponding achievable rateequivocation region are characterized. Of particular interest is the novel NoiseForwarding (NF) strategy, where the relay node sends codewords independent of the source message to confuse the eavesdropper. This strategy is used to illustrate the deaf helper phenomenon, where the relay is able to facilitate secure communications while being totally ignorant of the transmitted messages. Furthermore, NF is shown to increase the secrecy capacity in the reversely degraded scenario, where the relay node fails to offer performance gains in the classical setting. The gain offered by the proposed cooperation strategies is then proved theoretically and validated numerically in the additive White Gaussian Noise (AWGN) channel. I.
Towards the secrecy capacity of the Gaussian MIMO wiretap channel: The 221 channel
 IEEE TRANSACTIONS ON INFORMATION THEORY
, 2009
"... We find the secrecy capacity of the 221 Gaussian MIMO wiretap channel, which consists of a transmitter and a receiver with two antennas each, and an eavesdropper with a single antenna. We determine the secrecy capacity of this channel by proposing an achievable scheme and then developing a tight ..."
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Cited by 79 (20 self)
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We find the secrecy capacity of the 221 Gaussian MIMO wiretap channel, which consists of a transmitter and a receiver with two antennas each, and an eavesdropper with a single antenna. We determine the secrecy capacity of this channel by proposing an achievable scheme and then developing a tight upper bound that meets the proposed achievable secrecy rate. We show that, for this channel, Gaussian signalling in the form of beamforming is optimal, and no preprocessing of information is necessary.
The Secrecy Capacity Region of the Gaussian MIMO MultiReceiver Wiretap Channel
, 2009
"... In this paper, we consider the Gaussian multipleinput multipleoutput (MIMO) multireceiver wiretap channel in which a transmitter wants to have confidential communication with an arbitrary number of users in the presence of an external eavesdropper. We derive the secrecy capacity region of this ch ..."
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Cited by 70 (23 self)
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In this paper, we consider the Gaussian multipleinput multipleoutput (MIMO) multireceiver wiretap channel in which a transmitter wants to have confidential communication with an arbitrary number of users in the presence of an external eavesdropper. We derive the secrecy capacity region of this channel for the most general case. We first show that even for the singleinput singleoutput (SISO) case, existing converse techniques for the Gaussian scalar broadcast channel cannot be extended to this secrecy context, to emphasize the need for a new proof technique. Our new proof technique makes use of the relationships between the minimummeansquareerror and the mutual information, and equivalently, the relationships between the Fisher information and the differential entropy. Using the intuition gained from the converse proof of the SISO channel, we first prove the secrecy capacity region of the degraded MIMO channel, in which all receivers have the same number of antennas, and the noise covariance matrices can be arranged according to a positive semidefinite order. We then generalize this result to the aligned case, in which all receivers have the same number of antennas, however there is no order among the noise covariance matrices. We accomplish this task by using the channel enhancement technique. Finally, we find the secrecy capacity region of the general MIMO channel by using some limiting arguments on the secrecy capacity region of the aligned MIMO channel. We show that the capacity achieving coding scheme is a variant of dirtypaper coding with Gaussian signals.
The wiretap channel with feedback: Encryption over the channel
 IEEE TRANS. INF. THEORY
, 2008
"... In this work, the critical role of noisy feedback in enhancing the secrecy capacity of the wiretap channel is established. Unlike previous works, where a noiseless public discussion channel is used for feedback, the feedforward and feedback signals share the same noisy channel in the present model ..."
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Cited by 59 (8 self)
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In this work, the critical role of noisy feedback in enhancing the secrecy capacity of the wiretap channel is established. Unlike previous works, where a noiseless public discussion channel is used for feedback, the feedforward and feedback signals share the same noisy channel in the present model. Quite interestingly, this noisy feedback model is shown to be more advantageous in the current setting. More specifically, the discrete memoryless moduloadditive channel with a fullduplex destination node is considered first, and it is shown that the judicious use of feedback increases the secrecy capacity to the capacity of the source–destination channel in the absence of the wiretapper. In the achievability scheme, the feedback signal corresponds to a private key, known only to the destination. In the halfduplex scheme, a novel feedback technique that always achieves a positive perfect secrecy rate (even when the source–wiretapper channel is less noisy than the source–destination channel) is proposed. These results hinge on the moduloadditive property of the channel, which is exploited by the destination to perform encryption over the channel without revealing its key to the source. Finally, this scheme is extended to the continuous real valued modulo channel where it is shown that the secrecy capacity with feedback is also equal to the capacity in the absence of the wiretapper.
Secrecy in Cooperative Relay Broadcast Channels
, 2008
"... We investigate the effects of user cooperation on the secrecy of broadcast channels by considering a cooperative relay broadcast channel. We show that user cooperation can increase the achievable secrecy region. We propose an achievable scheme that combines Marton’s coding scheme for broadcast chann ..."
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Cited by 54 (13 self)
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We investigate the effects of user cooperation on the secrecy of broadcast channels by considering a cooperative relay broadcast channel. We show that user cooperation can increase the achievable secrecy region. We propose an achievable scheme that combines Marton’s coding scheme for broadcast channels and Cover and El Gamal’s compressandforward scheme for relay channels. We derive outer bounds for the rateequivocation region using auxiliary random variables for singleletterization. Finally, we consider a Gaussian channel and show that both users can have positive secrecy rates, which is not possible for scalar Gaussian broadcast channels without cooperation.
Cooperation with an untrusted relay: a secrecy perspective
 IEEE TRANSACTIONS ON INFORMATION THEORY
, 2010
"... We consider the communication scenario where a sourcedestination pair wishes to keep the information secret from a relay node despite wanting to enlist its help. For this scenario, an interesting question is whether the relay node should be deployed at all. That is, whether cooperation with an untr ..."
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Cited by 53 (13 self)
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We consider the communication scenario where a sourcedestination pair wishes to keep the information secret from a relay node despite wanting to enlist its help. For this scenario, an interesting question is whether the relay node should be deployed at all. That is, whether cooperation with an untrusted relay node can ever be beneficial. We first provide an achievable secrecy rate for the general untrusted relay channel, and proceed to investigate this question for two types of relay networks with orthogonal components. For the first model, there is an orthogonal link from the source to the relay. For the second model, there is an orthogonal link from the relay to the destination. For the first model, we find the equivocation capacity region and show that answer is negative. In contrast, for the second model, we find that the answer is positive. Specifically, we show, by means of the achievable secrecy rate based on compressandforward, that by asking the untrusted relay node to relay information, we can achieve a higher secrecy rate than just treating the relay as an eavesdropper. For a special class of the second model, where the relay is not interfering itself, we derive an upper bound for the secrecy rate using an argument whose net effect is to separate the eavesdropper from the relay. The merit of the new upper bound is demonstrated on two channels that belong to this special class. The Gaussian case of the second model mentioned above benefits from this approach in that the new upper bound improves the previously known bounds. For the Cover–Kim deterministic relay channel, the new upper bound finds the secrecy capacity when the sourcedestination link is not worse than the sourcerelay link, by matching with achievable rate we present.
Providing Secrecy With Structured Codes: Tools and Applications to TwoUser Gaussian Channels
, 2009
"... Recent results have shown that structured codes can be used to construct good channel codes, source codes and physical layer network codes for Gaussian channels. For Gaussian channels with secrecy constraints, however, efforts to date rely on random codes. In this work, we advocate that structured c ..."
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Cited by 45 (17 self)
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Recent results have shown that structured codes can be used to construct good channel codes, source codes and physical layer network codes for Gaussian channels. For Gaussian channels with secrecy constraints, however, efforts to date rely on random codes. In this work, we advocate that structured codes are useful for providing secrecy, and show how to compute the secrecy rate when structured codes are used. In particular, we solve the problem of bounding equivocation rates with one important class of structured codes, i.e., nested lattice codes. Having established this result, we next demonstrate the use of structured codes for secrecy in twouser Gaussian channels. In particular, with structured codes, we prove that a positive secure degree of freedom is achievable for a large class of fully connected Gaussian channels as long as the channel is not degraded. By way of this, for these channels, we establish that structured codes outperform Gaussian random codes at high SNR. This class of channels include the twouser multiple access wiretap channel, the twouser interference channel with confidential messages and the twouser interference wiretap channel. A notable consequence of this result is that, unlike the case with Gaussian random codes, using structured codes for both transmission and cooperative jamming, it is possible to achieve an arbitrary large secrecy rate given enough power.