15,948 research outputs found
Covert channel detection using Information Theory
This paper presents an information theory based detection framework for
covert channels. We first show that the usual notion of interference does not
characterize the notion of deliberate information flow of covert channels. We
then show that even an enhanced notion of "iterated multivalued interference"
can not capture flows with capacity lower than one bit of information per
channel use. We then characterize and compute the capacity of covert channels
that use control flows for a class of systems.Comment: In Proceedings SecCo 2010, arXiv:1102.516
Fundamental Limits of Covert Communication
Traditional security (e.g., encryption) prevents unauthorized access to message content; however, detection of the mere presence of a message can have significant negative impact on the privacy of the communicating parties. Unlike these standard methods, covert or low probability of detection (LPD) communication not only protects the information contained in a transmission from unauthorized decoding, but also prevents the detection of a transmission in the first place. In this thesis we investigate the fundamental laws of covert communication.
We first study covert communication over additive white Gaussian noise (AWGN) channels, a standard model for radio-frequency (RF) communication. We present a square root limit on the amount of information transmitted covertly and reliably over such channels. Specifically, we prove that if the transmitter has the channels to the intended receiver and the warden that are both AWGN, then O(\sqrt{n}) covert bits can be reliably transmitted to the receiver in n uses of the channel. Conversely, attempting to transmit more than O(\sqrt{n}) bits either results in detection by the warden with probability one or a non-zero probability of decoding error at the receiver as n--\u3e\infty.
Next we study the impact of warden\u27s ignorance of the communication attempt time. We prove that if the channels from the transmitter to the intended receiver and the warden are both AWGN, and if a single n-symbol period slot out of T(n) such slots is selected secretly (forcing the warden to monitor all T(n) slots), then O(\min{\sqrt{n\log T(n)},n}) covert bits can be transmitted reliably using this slot. Conversely, attempting to transmit more than O(\sqrt{n\log T(n)}) bits either results in detection with probability one or a non-zero probability of decoding error at the receiver.
We then study covert optical communication and characterize the ultimate limit of covert communication that is secure against the most powerful physically-permissible adversary. We show that, although covert communication is impossible when a channel injects the minimum noise allowed by quantum mechanics, it is attainable in the presence of any noise excess of this minimum (such as the thermal background). In this case, O(\sqrt{n}) covert bits can be transmitted reliably in n optical channel uses using standard optical communication equipment. The all-powerful adversary may intercept all transmitted photons not received by the intended receiver, and employ arbitrary quantum memory and measurements. Conversely, we show that this square root scaling cannot be circumvented. Finally, we corroborate our theory in a proof-of-concept experiment on an optical testbed
Fundamental limits of quantum-secure covert optical sensing
We present a square root law for active sensing of phase of a single
pixel using optical probes that pass through a single-mode lossy thermal-noise
bosonic channel. Specifically, we show that, when the sensor uses an -mode
covert optical probe, the mean squared error (MSE) of the resulting estimator
scales as ; improving the
scaling necessarily leads to detection by the adversary with high probability.
We fully characterize this limit and show that it is achievable using laser
light illumination and a heterodyne receiver, even when the adversary captures
every photon that does not return to the sensor and performs arbitrarily
complex measurement as permitted by the laws of quantum mechanics.Comment: 13 pages, 1 figure, submitted to ISIT 201
Optimal Throughput for Covert Communication Over a Classical-Quantum Channel
This paper considers the problem of communication over a memoryless
classical-quantum wiretap channel subject to the constraint that the
eavesdropper on the channel should not be able to learn whether the legitimate
parties are using the channel to communicate or not. Specifically, the relative
entropy between the output quantum states at the eavesdropper when a codeword
is transmitted and when no input is provided must be sufficiently small.
Extending earlier works, this paper proves the "square-root law" for a broad
class of classical-quantum channels: the maximum amount of information that can
be reliably and covertly transmitted over uses of such a channel scales
like . The scaling constant is also determined.Comment: Corrected version of a paper presented at ITW 2016. In the ITW paper,
the denominator in the main formula (10) was incorrect. The current version
corrects this mistake and adds an appendix for its derivatio
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