We study covert classical communication over a quantum multiple-access channel (MAC) with a helper. Specifically, we consider three transmitters, where one transmitter helps the other two transmitters communicate covertly with a receiver. We demonstrate the feasibility of achieving a positive covert rate over this channel and establish an achievable rate region. Our result recovers as a special case known results for classical communication over classical MACs with a degraded message set, classical communication over quantum MACs, and classical communication over MACs with a helper. To the best of our knowledge, our result is the first to achieve covert communication with positive rates over both classical and quantum MACs.

We study covert communication and covert secret key generation with positive rates over channels with causal Channel State Information (CSI) at the transmitter. Specifically, we consider a state-dependent Discrete Memoryless Channel (DMC) where the transmitter has causal access to the CSI, and aims to communicate covertly with the receiver while simultaneously generating a covert secret key shared with the receiver. We derive an achievable rate region for this problem, which recovers as a special case the best-known results for covert communication over channels with CSI. To the best of our knowledge, our results are the first instance of achieving a positive rate for covert secret key generation.

Noiseless private side information does not reduce the download cost in Symmetric Private Information Retrieval (SPIR) unless the client knows all but one file. While this is a pessimistic result, we explore in this paper whether noisy client side information available at the client helps decrease the download cost in the context of SPIR with colluding and replicated servers. Specifically, we assume that the client possesses noisy side information about each stored file, which is obtained by passing each file through one of D possible discrete memoryless test channels. The statistics of the test channels are known by the client and by all the servers, but the mapping$\boldsymbol {\mathcal {M}}$between the files and the test channels is unknown to the servers. We study this problem under two privacy metrics. Under the first metric, the client wants to preserve the privacy of its file selection and the mapping$\boldsymbol {\mathcal {M}}$, and the servers want to preserve the privacy of all the non-selected files. Under the second metric, the client is willing to reveal the index of the test channel that is associated with its desired file. For both privacy metrics, we derive the optimal common randomness and download cost. Our setup generalizes SPIR with colluding servers and SPIR with private noiseless side information. Unlike noiseless side information, our results demonstrate that noisy side information can reduce the download cost, even when the client does not have noiseless knowledge of all but one file.

We study covert communication and covert secret key generation with positive rates over quantum state-dependent channels. Specifically, we consider fully quantum state-dependent channels when the transmitter shares an entangled state with the channel. We study this problem setting under two security metrics. For the first security metric, the transmitter aims to communicate covertly with the receiver while simultaneously generating a covert secret key, and for the second security metric, the transmitter aims to transmit a secure message covertly and generate a covert secret key with the receiver simultaneously. Our main results include one-shot and asymptotic achievable positive covert-secret key rate pairs for both security metrics. Our results recover as a special case the best-known results for covert communication over state-dependent classical channels. To the best of our knowledge, our results are the first instance of achieving a positive rate for covert secret key generation and the first instance of achieving a positive covert rate over a quantum channel. Additionally, we show that our results are optimal when the channel is classical and the state is available non-causally at both the transmitter and the receiver.

This paper studies covert communication over channels with Action-Dependent State Information (ADSI) when the state is available either non-causally or causally at the transmitter. Covert communication refers to reliable communication between a transmitter and a receiver while ensuring a low probability of detection by an adversary, which we refer to as “warden”. It is well known that in a point-to-point Discrete Memoryless Channel (DMC), it is possible to communicate on the order of$\sqrt {N}$bits reliably and covertly over N channel uses while the transmitter and the receiver are required to share a secret key on the order of$\sqrt {N}$bits. This paper studies achieving reliable and covert communication of positive rate, i.e., reliable and covert communication on the order of N bits in N channel uses, over a channel with ADSI while the transmitter has non-causal or causal access to the ADSI, and the transmitter and the receiver share a secret key of negligible rate. We derive achievable rates for both the non-causal and causal scenarios by using block-Markov encoding and secret key generation from the ADSI, which subsumes the best achievable rates for channels with random states. We also derive upper bounds, for both non-causal and causal scenarios, that meet our achievable rates for some special cases. As an application of our problem setup, we study covert communication over channels with rewrite options, which are closely related to recording covert information on memory, and show that a positive covert rate can be achieved in such channels. As a special case of our problem, we study the Additive White Gaussian Noise (AWGN) channels and provide lower and upper bounds on the covert capacity that meet when the transmitter and the receiver share a secret key of sufficient rate and when the warden’s channel is noisier than the legitimate receiver channel. As another application of our problem setup, we show that cooperation can lead to a positive covert rate in Gaussian channels. A few other examples are also worked out in detail.

Noiseless private side information does not reduce the download cost in Symmetric Private Information Retrieval (SPIR) unless the client knows all but one file. While this is a pessimistic result, we explore in this paper whether noisy private side information available at the client helps decrease the download cost in the context of SPIR with colluding and replicated servers. Specifically, we assume that the client possesses noisy side information about each stored file, which is obtained by passing each file through one of$D$possible discrete memoryless test channels. The statistics of the test channels are known by the client and by all the servers, but the mapping$\mathcal{M}$between the files and the test channels is unknown to the servers. We study this problem under two privacy metrics. Under the first metric, the client wants to preserve the privacy of its file selection and the mapping$\mathcal{M}$, and the servers want to preserve the privacy of all the non-selected files. Under the second metric, the client is willing to reveal the index of the test channel that is associated with its desired file. For both privacy metrics, we derive the optimal common randomness and download cost. Our setup generalizes SPIR with colluding servers and SPIR with private noiseless side information. Unlike noiseless side information, our results demonstrate that noisy side information can reduce the download cost, even when the client does not have noiseless knowledge of all but one file.

We show that it is possible to achieve a positive covert communication rate over state-dependent quantum channels. Specifically, we consider fully quantum state-dependent channels when the transmitter shares an entangled state with the channel. To the best of our knowledge, this is the first instance of achieving a positive covert rate over a quantum channel. Our main results include a one-shot achievable covert rate and asymptotic achievable covert rates that recover, as a special case, known results for classical channels.

Consider Private Information Retrieval (PIR), where a client wants to retrieve one file out of$K$files that are replicated in$N$different servers and the client selection must remain private when up to$T$servers may collude. Additionally, suppose that the client has noisy side information about each of the$K$files, and the side information about a specific file is obtained by passing this file through one of$D$possible discrete memoryless test channels, where$D\le K$. While the statistics of the test channels are known by the client and by all the servers, the specific mapping$\boldsymbol { \mathcal {M}}$between the files and the test channels is unknown to the servers. We study this problem under two different privacy metrics. Under the first privacy metric, the client wants to preserve the privacy of its desired file selection and the mapping$\boldsymbol { \mathcal {M}}$. Under the second privacy metric, the client wants to preserve the privacy of its desired file and the mapping$\boldsymbol { \mathcal {M}}$but is willing to reveal the index of the test channel that is associated to its desired file. For both of these two privacy metrics, we derive the optimal normalized download cost. Our problem setup generalizes PIR with colluding servers, PIR with private noiseless side information, and PIR with private side information under storage constraints.

Consider Private Information Retrieval (PIR), where a client wants to retrieve one file out of K files that are replicated in N different servers and the client selection must remain private when up to T servers may collude. Additionally, suppose that the client has noisy side information about each of the K files, and the side information about a specific file is obtained by passing this file through one of D possible discrete memoryless test channels, where D≤K. While the statistics of the test channels are known by the client and by all the servers, the specific mapping ${\mathcal{M}}$ between the files and the test channels is unknown to the servers. We study this problem when the client wants to preserve the privacy of its desired file selection and the mapping ${\mathcal{M}}$. For this problem setup, we derive the optimal download rate. Our problem setup generalizes PIR with private noiseless side information and PIR with private side information under storage constraints.

This paper studies covert communication over channels with action-dependent states when the state is available non-causally at the encoder. Covert communication refers to reliable communication between a transmitter and a receiver while ensuring low probability of detection at an adversary, which we refer to as "warden". It is well known that in a point to point Discrete Memoryless Channel (DMC), it is possible to communicate on the order of $\sqrt N $ bits reliably and covertly over N channel uses while the transmitter and the receiver are required to share a secret key on the order of $\sqrt N $ bits. This paper studies achieving positive covert and reliable communication rate, which is communication on the order of N bits over N channel uses, while the transmitter and the receiver share a secret key of negligible rate. We derive an achievable rate region by using block-Markov encoding and secret key generation from the Action-Dependent State Information (ADSI), which subsumes the best achievable rate region for channels with random states.

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.

Consider a source and multiple users who observe the independent and identically distributed (i.i.d.) copies of correlated Gaussian random variables. The source wishes to compress and store its observation in a public database such that (i) authorized sets of users can reconstruct the source with some distortion level, and (ii) information leakage to non-authorized sets of colluding users is minimized. In other words, the recovery of the data is restricted to a predefined access structure of the users. One of the main results of this paper is a closed-form characterization of the fundamental trade-off between source coding rate and the information leakage rate when any authorized set of users has "better" side information than any set of unauthorized users.

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 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 only$O(\sqrt{n})$covert bits over$n$channel 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.

Motivated in part by the problem of secure multicast distributed storage, we analyze secrecy rates for a channel in which two transmitters simultaneously multicast to two receivers in the presence of an eavesdropper. Achievable rates are calculated via extensions of a technique due to Chia and El Gamal and the method of output statistics of random binning. Outer bounds are derived for both the degraded and non-degraded versions of the channel, and examples are provided in which the inner and outer bounds meet. The inner bounds recover known results for the multiple-access wiretap channel, broadcast channel with confidential messages, and the compound MAC channel. An auxiliary result is also produced that derives an inner bound on the minimal randomness necessary to achieve secrecy in multiple-access wiretap channels.

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.

The authors study the problem of secret communication over a multiple‐access channel with a common message. Here, the authors assume that two transmitters have confidential messages, which must be kept secret from the wiretapper (the second receiver), and both of them have access to a common message which can be decoded by the two receivers. The authors call this setting as multiple‐access wiretap channel with common message (MAWC‐CM). For this setting, the authors derive general inner and outer bounds on the secrecy capacity region for the discrete memoryless case and show that these bounds meet each other for a special case called the switch channel. As well, for a Gaussian version of MAWC‐CM, the authors derive inner and outer bounds on the secrecy capacity region. Providing numerical results for the Gaussian case, the authors illustrate the comparison between the derived achievable rate region and the outer bound for the considered model and the capacity region of compound multiple access channel.

In this paper, we study the problem of secret communication over a compound Multiple Access Channel (MAC). In this channel, we assume that one of the transmitted messages is confidential, which is only decoded by its corresponding receiver and kept secret from the other receiver. We call this proposed setting the compound MAC with a confidential message. For this model, we derive general inner and outer bounds for both imperfect and perfect secrecy conditions for the second receiver. Also, as examples, we investigate less noisy and Gaussian versions of this channel, and extend the results of the discrete memoryless version to these cases. Moreover, providing numerical examples for the Gaussian case, we illustrate the comparison between achievable rate regions of compound MAC and compound MAC with a confidential message. In addition, for the Gaussian case, we show that using cooperative jamming strategy can increase the achievable secrecy rate between the legitimate transmitter and the receiver.

In this paper, we study the problem of secret communication over a Compound Multiple Access Channel (MAC). In this channel, we assume that one of the transmitted messages is confidential that is only decoded by its corresponding receiver and kept secret from the other receiver. For this proposed setting (compound MAC with confidential messages), we derive general inner and outer bounds on the secrecy capacity region. Also, as examples, we investigate `Less noisy' and `Gaussian' versions of this channel, and extend the results of the discrete memoryless version to these cases. Moreover, providing numerical examples for the Gaussian case, we illustrate the comparison between achievable rate regions of compound MAC and compound MAC with confidential messages.