This paper is eligible for the Jack Keil Wolf ISIT Student Paper Award. This paper investigates covert communication in the presence of a cooperative jammer. Covert communication refers to the inability of an adversary to distinguish data transmission from a so-called innocent symbol at the input. We consider three related problems: (1) a jammer without direct communication or coordination with the transmitter, (2) a jammer that cribs the output of the transmitter, and (3) a jammer that is able to coordinate with the transmitter via a secret key that is also shared with the legitimate receiver. For each model, we derive inner and outer bounds on the capacity region that are tight in some special cases. Unlike prior results in the literature, the jammer in our model does not have access to unlimited local randomness. In fact, uncovering the fundamental interplay between the covert communication rate, local randomness, and secret key rate, is one of the distinctions and contributions of the present work. In the context of a few specific channels, we calculate achievable covert rates to illuminate our results.
This paper is eligible for the Jack Keil Wolf ISIT Student Paper Award. This paper investigates covert communication in the presence of a cooperative jammer. Covert communication refers to the inability of an adversary to distinguish data transmission from a so-called innocent symbol at the input. We consider three related problems: (1) a jammer without direct communication or coordination with the transmitter, (2) a jammer that cribs the output of the transmitter, and (3) a jammer that is able to coordinate with the transmitter via a secret key that is also shared with the legitimate receiver. For each model, we derive inner and outer bounds on the capacity region that are tight in some special cases. Unlike prior results in the literature, the jammer in our model does not have access to unlimited local randomness. In fact, uncovering the fundamental interplay between the covert communication rate, local randomness, and secret key rate, is one of the distinctions and contributions of the present work. In the context of a few specific channels, we calculate achievable covert rates to illuminate our results.
We consider the problem of covert communication in the presence of a cooperative jammer. Covert communication refers to communication that is undetectable by an adversary, i.e., a scenario in which, despite ongoing communication, the output distribution observed by an adversary called the “warden” is indistinguishable from the distribution that would have been induced by an innocent channel-input symbol. It is known that in general, a transmitter and a receiver can communicate onlyO(n)covert bits overnchannel uses, i.e., zero rate. This paper shows that a cooperative jammer can facilitate the communication of positive covert rates, subject to the transmitter having non-causal access to the jammer signal. An achievable rate region is calculated that highlights the relation between the covert communication rate, jammer's randomness (expressed as a rate), and rate of a secret key shared between transmitter and receiver.
We consider the problem of covert communication over a state-dependent channel when the Channel State Information (CSI) is available either non-causally, causally, or strictly causally, either at the transmitter alone, or at both transmitter and receiver. Covert communication with respect to an adversary, called “warden,” is one in which, despite communication over the channel, the warden’s observation remains indistinguishable from an output induced by innocent channel-input symbols. Covert communication involves fooling an adversary in part by a proliferation of codebooks; for reliable decoding at the legitimate receiver, the codebook uncertainty is typically removed via a shared secret key that is unavailable to the warden. In contrast to previous work, we do not assume the availability of a large shared key at the transmitter and legitimate receiver. Instead, we only require a secret key with negligible rate to bootstrap the communication and our scheme extracts shared randomness from the CSI in a manner that keeps it secret from the warden, despite the influence of the CSI on the warden’s output. When CSI is available at the transmitter and receiver, we derive the covert capacity region. When CSI is only available at the transmitter, we derive inner and outer bounds on the covert capacity. We also provide examples for which the covert capacity is positive with knowledge of CSI but is zero without it.
We consider the problem of covert communication when Channel State Information (CSI) is available non-causally, causally, and strictly causally at both transmitter and receiver, as well as the case when channel state information is only available at the transmitter. Covert communication with respect to an adversary referred to as the "warden", is one in which the distribution induced during communication at the channel output observed by the warden is identical to the output distribution conditioned on an innocent channel-input symbol. In contrast to previous work, we do not assume the availability of a shared key at the transmitter and legitimate receiver; instead shared randomness is extracted from the channel state, in a manner that keeps it secret from the warden despite the influence of the channel state on the warden's output. When CSI is available at both transmitter and receiver, we derive the covert capacity region; when CSI is only available at the transmitter, we derive inner and outer bounds on the covert capacity. We also derive the covert capacity when the warden's channel is less noisy with respect to the legitimate receiver. We provide examples for which covert capacity is zero without channel state information, but is positive in the presence of channel state information.
We consider the problem of covert communication over a state-dependent channel, for which the transmitter and the legitimate receiver have non-causal access to the channel state information. Covert communication with respect to an adversary, referred to as the “warden,” is one in which the distribution induced during communication at the channel output observed by the warden is identical to the output distribution conditioned on an inactive channel-input symbol. Covert communication involves fooling an adversary in part by a proliferation of codebooks; for reliable decoding at the legitimate receiver the codebook uncertainty is removed via a shared secret key that is unavailable to the warden. Unlike earlier work in state-dependent covert communication, we do not assume the availability of a shared key at the transmitter and legitimate receiver. Rather, a shared randomness is extracted at the transmitter and the receiver from the channel state, in a manner that keeps the shared randomness secret from the warden despite the influence of the channel state on the warden's output. An inner bound on the covert capacity, in the absence of an externally provided secret key, is derived.
This study investigates covert communication in the presence of a half-duplex amplify-and-forward (AF) relay, while accounting for transceiver hardware impairments. A cooperative jamming strategy and channel uncertainty are employed to achieve covertness. For a trusted relay, informed jammers mitigate the effect of artificial noise (AN) at the legitimate receiver and increase the warden’s uncertainty, thereby enhancing the covert rate. For an untrusted relay, the jammer must emit AN while the data signal is transmitted toward the untrusted relay to reduce the untrusted relay’s signal-to-interference-plus-noise ratio (SINR), which poses a challenge for deploying an informed jammer. The results show that, in both trusted and untrusted relay scenarios, increasing the transmit power yields only marginal performance gains due to hardware impairments, highlighting the importance of high-quality transceivers and compensation algorithms. Notably, under specific conditions, impairments in the legitimate receiver’s transmitter can slightly enhance performance in the trusted relay case, while in untrusted relay scenarios, impairments in any legitimate node degrade covert communication performance. Differences in hardware equipment quality between the transmitter (or retransmitter) and its associated jammer also affect the warden’s ability to detect the transmission.
Recent work has established that when transmitter Alice wishes to communicate reliably to recipient Bob without detection by warden Willie, with additive white Gaussian noise (AWGN) channels between all parties, communication is limited to O(√n) bits in n channel uses. However, this result is predicated on Willie having an accurate statistical characterization of the background noise. When Willie has uncertainty about his noise characteristics and his receiver is limited to a power detector, O(n) bits can be covertly delivered. Here, we establish covert communication of O(n) bits in n channel uses while: (i) generalizing the environment; and (ii) removing any restrictions on Willie's receiver. We consider the case where an additional node, called the "jammer", is present to help Alice and Bob communicate covertly. This jammer is termed "uninformed", as it does not know the content or timing of Alice's transmission. We consider both AWGN channels and a scenario with a block faded jammer with a single fade per codeword. In these scenarios, we are able to establish the optimality of the power detector for Willie, from which the achievability of reliable and covert communication at a positive rate follows.