# Information Bytes

Matthieu Bloch
School of Electrical and Computer Engineering
Georgia Institute of Technology

# Recent works

1. M. Tahmasbi and M. R. Bloch, “Covert Secret Key Generation with an Active Warden.” submitted to IEEE Transactions on Information Forensics and Security, Jan. 2019.

We investigate the problem of covert and secret key generation over a discrete memoryless channel model with one way public discussion and in presence of an active warden who can arbitrarily vary its channel and tamper with the main channel when an information symbol is sent. In this scenario, we develop an adaptive protocol that is required to conceal not only the key but also whether a protocol is being implemented. Based on the adversary’s actions, this protocol generates a key whose size depends on the adversary’s actions. Moreover, for a passive adversary and for some models that we identify, we show that covert secret key generation is possible and characterize the covert secret key capacity in special cases; in particular, the covert secret key capacity is sometimes equal to the covert capacity of the channel, so that secrecy comes “for free."

@misc{Tahmasbi2019,
author = {Tahmasbi, Mehrdad and Bloch, Matthieu R},
title = {Covert Secret Key Generation with an Active Warden},
howpublished = {submitted to \emph{IEEE Transactions on Information Forensics and Security}},
month = jan,
year = {2019},
eprint = {1901.02044},
groups = {Steganography and covert communications}
}


2. M. Le Treust and M. R. Bloch, “State Leakage and Coordination of Actions: Core of the Receiver’s Knowledge.” submitted to IEEE Transactions on Information Theory, Dec. 2018.

We revisit the problems of state masking and state amplification through the lens of empirical coordination by considering a state-dependent channel in which the encoder has causal and strictly causal state knowledge. We show that the problem of empirical coordination provides a natural framework in which to jointly study the problems of reliable communication, state masking, and state amplification. We characterize the regions of rate-equivocation-coordination trade-offs for several channel models with causal and strictly causal state knowledge. We introduce the notion of “core of the receiver’s knowledge” to capture what the decoder can infer about all the signals involved in the model. We exploit this result to solve a channel state estimation zero-sum game in which the encoder prevents the decoder to estimate the channel state accurately.

@misc{LeTreust2018,
author = {{Le Treust}, Ma\"el and Bloch, Matthieu R},
title = {State Leakage and Coordination of Actions: Core of the Receiver's Knowledge},
howpublished = {submitted to \emph{IEEE Transactions on Information Theory}},
month = dec,
year = {2018},
eprint = {1812.07026}
}


3. H. Zivari-Fard, M. Bloch, and A. Nosratinia, “Secrecy Rates for a Channel With Two Senders and Two Receivers.” submitted to IEEE Transactions on Information Theory, Dec. 2018.

@misc{Zivari-Fard2018,
author = {Zivari-Fard, Hassan and Bloch, Matthieu and Nosratinia, Aria},
title = {Secrecy Rates for a Channel With Two Senders and Two Receivers},
howpublished = {submitted to \emph{IEEE Transactions on Information Theory}},
month = dec,
year = {2018}
}


4. I. A. Kadampot, M. Tahmasbi, and M. R. Bloch, “Multilevel-Coded Pulse-Position Modulation for Covert Communications over Binary-Input Discrete Memoryless Channels.” submitted to IEEE Transactions on Information Theory, Nov. 2018.

We develop a low-complexity coding scheme to achieve covert communications over binary-input discrete memoryless channels (BI-DMCs). We circumvent the impossibility of covert communication with linear codes by introducing non-linearity through the use of pulse position modulation (PPM) and multilevel coding (MLC). We show that the MLC-PPM scheme exhibits many appealing properties; in particular, the channel at a given index level remains stationary as the number of level increases, which allows one to use families of channel capacity- and channel resolvability-achieving codes to concretely instantiate the covert communication scheme.

@misc{Kadampot2018a,
author = {Kadampot, Ishaque Ashar and Tahmasbi, Mehrdad and Bloch, Matthieu R},
title = {Multilevel-Coded Pulse-Position Modulation for Covert Communications over Binary-Input Discrete Memoryless Channels},
howpublished = {submitted to \emph{IEEE Transactions on Information Theory}},
month = nov,
year = {2018},
eprint = {1811.09695}
}