# Information Bytes

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

# Recent works

1. N. Helal, M. Bloch, and A. Nosratinia, “Cooperative Resolvability and Secrecy in the Cribbing Multiple-Access Channel,” IEEE Transactions on Information Theory, vol. 66, no. 9, pp. 5429–5447, Sep. 2020.

We study channel resolvability for the discrete memoryless multiple-access channel with cribbing, i.e., the characterization of the amount of randomness required at the inputs to approximately produce a chosen i.i.d. output distribution according to Kullback-Leibler divergence. We analyze resolvability rates when one encoder cribs (i) the input of the other encoder; or the output of the other encoder, (ii) non-causally, (iii) causally, or (iv) strictly-causally. For scenarios (i)-(iii), we exactly characterize the channel resolvability region. For (iv), we provide inner and outer bounds for the channel resolvability region; the crux of our achievability result is to handle the strict causality constraint with a block-Markov coding scheme in which dependencies across blocks are suitably hidden. Finally, we leverage the channel resolvability results to derive achievable secrecy rate regions for each of the cribbing scenarios under strong secrecy constraints.We study channel resolvability for the discrete memoryless multiple-access channel with cribbing, i.e., the characterization of the amount of randomness required at the inputs to approximately produce a chosen i.i.d. output distribution according to Kullback-Leibler divergence. We analyze resolvability rates when one encoder cribs (i) the input of the other encoder; or the output of the other encoder, (ii) non-causally, (iii) causally, or (iv) strictly-causally. For scenarios (i)-(iii), we exactly characterize the channel resolvability region. For (iv), we provide inner and outer bounds for the channel resolvability region; the crux of our achievability result is to handle the strict causality constraint with a block-Markov coding scheme in which dependencies across blocks are suitably hidden. Finally, we leverage the channel resolvability results to derive achievable secrecy rate regions for each of the cribbing scenarios under strong secrecy constraints.

@article{Helhal2018a,
author = {Helal, Noha and Bloch, Matthieu and Nosratinia, Aria},
title = {Cooperative Resolvability and Secrecy in the Cribbing Multiple-Access Channel},
journal = {IEEE Transactions on Information Theory},
year = {2020},
volume = {66},
number = {9},
pages = {5429-5447},
month = sep,
doi = {10.1109/TIT.2020.2995565},
eprint = {1811.11649},
file = {:2020-Helal-IEEETransIT.pdf:PDF},
howpublished = {accepted for \emph{IEEE Transactions on Information Theory}}
}


2. G. Cervia, L. Luzzi, M. Le Treust, and M. Bloch, “Strong Coordination of Signals and Actions over Noisy Channels with two-sided State Information,” IEEE Transactions on Information Theory, vol. 66, no. 8, pp. 4681–4708, Aug. 2020.

We consider a network of two nodes separated by a noisy channel with two-sided state information, in which the input and output signals have to be coordinated with the source and its reconstruction. In the case of non-causal encoding and decoding, we propose a joint source-channel coding scheme and develop inner and outer bounds for the strong coordination region. While the inner and outer bounds do not match in general, we provide a complete characterization of the strong coordination region in three particular cases: i) when the channel is perfect; ii) when the decoder is lossless; and iii) when the random variables of the channel are independent from the random variables of the source. Through the study of these special cases, we prove that the separation principle does not hold for joint source-channel strong coordination. Finally, in the absence of state information, we show that polar codes achieve the best known inner bound for the strong coordination region, which therefore offers a constructive alternative to random binning and coding proofs.

@article{Cervia2018,
author = {Cervia, Giulia and Luzzi, Laura and {Le Treust}, Ma\"el and Bloch, Matthieu},
title = {Strong Coordination of Signals and Actions over Noisy Channels with two-sided State Information},
journal = {IEEE Transactions on Information Theory},
year = {2020},
volume = {66},
number = {8},
pages = {4681-4708},
month = aug,
doi = {10.1109/TIT.2020.2984345},
eprint = {1801.10543},
file = {:2020-Cervia-IEEETransIT.pdf:PDF},
howpublished = {accepted to \emph{IEEE Transactions on Information Theory}}
}


3. M. Tahmasbi and M. R. Bloch, “Covert and secret key expansion over quantum channels under collective attacks.” accepted to IEEE Transactions on Information Theory, Aug. 2020.

We consider an enhanced measure of security for a quantum key distribution protocol, in which we require not only that the adversary obtains no information about the key but also remains unaware that a key generation protocol has been executed. When the adversary applies the same quantum channel independently to each transmitted quantum state, akin to a collective attack in the quantum key distribution literature, we propose a protocol that achieves covert and secret key expansion under mild restrictions. A crucial component of the protocol is a covert estimation stage, which is then combined with universal channel coding for reliability and resolvability in the covert regime.

@misc{Tahmasbi2019a,
author = {Tahmasbi, Mehrdad and Bloch, Matthieu R},
title = {Covert and secret key expansion over quantum channels under collective attacks},
howpublished = {accepted to \emph{IEEE Transactions on Information Theory}},
month = aug,
year = {2020},
doi = {10.1109/TIT.2020.3021595}
}


4. M. Tahmasbi and M. R. Bloch, “Towards Undetectable Quantum Key Distribution over Bosonic Channels.” accepted to IEEE Journal of Selected Topics in Information Theory, Aug. 2020.

We propose a protocol based on pulse-position modulation and multi-level coding that allows one to bootstrap traditional quantum key distribution protocols while ensuring covertness, in the sense that no statistical test by the adversary can detect the presence of communication over the quantum channel better than a random guess. When run over a bosonic channel, our protocol can leverage existing discrete-modulated continuous-variable protocols. Since existing techniques to bound Eve’s information do not directly apply, we develop a new bound that results in positive, although very low, throughput for a range of channel parameters. The analysis of the protocol performance shows that covert secret key expansion is possible using a public authenticated classical channel and a quantum channel largely but not fully under the control of an adversary, which we precisely define. We also establish a converse result showing that, under the golden standard of quantum key distribution, by which the adversary completely controls the quantum channel, no covert key generation is possible.We propose a protocol based on pulse-position modulation and multi-level coding that allows one to bootstrap traditional quantum key distribution protocols while ensuring covertness, in the sense that no statistical test by the adversary can detect the presence of communication over the quantum channel better than a random guess. When run over a bosonic channel, our protocol can leverage existing discrete-modulated continuous-variable protocols. Since existing techniques to bound Eve’s information do not directly apply, we develop a new bound that results in positive, although very low, throughput for a range of channel parameters. The analysis of the protocol performance shows that covert secret key expansion is possible using a public authenticated classical channel and a quantum channel largely but not fully under the control of an adversary, which we precisely define. We also establish a converse result showing that, under the golden standard of quantum key distribution, by which the adversary completely controls the quantum channel, no covert key generation is possible.

@misc{Tahmasbi2020,
author = {Tahmasbi, Mehrdad and Bloch, Matthieu R.},
title = {Towards Undetectable Quantum Key Distribution over Bosonic Channels},
howpublished = {accepted to \emph{IEEE Journal of Selected Topics in Information Theory}},
month = aug,
year = {2020},
doi = {10.1109/JSAIT.2020.3017212},
eprint = {1904.12363}
}