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arXiv:1609.09454 · IEEE Information Theory Workshop (ITW)

Keyless authentication in the presence of a simultaneously transmitting adversary

Eric Graves, Paul L. Yu, Predrag Spasojević

Published Sep 1, 2016• 15 citations
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Abstract

If Alice must communicate with Bob over a channel shared with the adversarial Eve, then Bob must be able to validate the authenticity of the message. In particular we consider the model where Alice and Eve share a discrete memoryless multiple access channel with Bob, thus allowing simultaneous transmissions from Alice and Eve. By traditional random coding arguments, we demonstrate an inner bound on the rate at which Alice may transmit, while still granting Bob the ability to authenticate. Furthermore this is accomplished in spite of Alice and Bob lacking a pre-shared key, as well as allowing Eve prior knowledge of both the codebook Alice and Bob share and the messages Alice transmits.

DOI
10.1109/itw.2016.7606824

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•Jun 4, 2010•5 citations
If Alice must communicate with Bob over a channel shared with the adversarial Eve, then Bob must be able to validate the authenticity of the message. In particular we consider the model where Alice and Eve share a discrete memoryless multiple access channel with Bob, thus allowing simultaneous transmissions from Alice and Eve. By traditional random coding arguments, we demonstrate an inner bound on the rate at which Alice may transmit, while still granting Bob the ability to authenticate. Furthermore this is accomplished in spite of Alice and Bob lacking a pre-shared key, as well as allowing Eve prior knowledge of both the codebook Alice and Bob share and the messages Alice transmits.
We consider a setup in which the channel from Alice to Bob is less noisy than the channel from Eve to Bob. We show that there exist encoding and decoding which accomplish error correction and authentication simultaneously; that is, Bob is able to correctly decode a message coming from Alice and reject a message coming from Eve with high probability. The system does not require any secret key shared between Alice and Bob, provides information theoretic security, and can safely be composed with other protocols in an arbitrary context.
We consider a scenario in which K transmitters attempt to communicate covert messages reliably to a legitimate receiver over a discrete memoryless multiple-access channel (MAC) while simultaneously escaping detection from an adversary who observes their communication through another discrete memoryless MAC. We assume that each transmitter may use a secret key that is shared only between itself and the legitimate receiver. We show that each of the K transmitters can transmit on the order of √n reliable and covert bits per n channel uses, exceeding which, the warden will be able to detect the communication. We identify the optimal pre-constants of the scaling, which leads to a complete characterization of the covert capacity region of the K-user binary-input MAC. We show that, asymptotically, all sum-rate constraints are inactive unlike the traditional MAC capacity region. We also characterize the channel conditions that have to be satisfied for the transmitters to operate without a secret key.
Suppose that a transmitter Alice potentially wishes to communicate with a receiver Bob over an adversarially jammed binary channel. An active adversary James eavesdrops on their communication over a binary symmetric channel (BSC(q)), and may maliciously flip (up to) a certain fraction p of their transmitted bits based on his observation. We consider a setting where the communication must be simultaneously covert as well as reliable, i.e., James should be unable to accurately distinguish whether or not Alice is communicating, while Bob should be able to correctly recover Alice's message with high probability regardless of the adversarial jamming strategy. We show that, unlike the setting with passive adversaries, reliable covert communication against active adversaries requires Alice and Bob to have a shared key (of length at least Ω(log n)) even when Bob has a better channel than James. We present inner and outer bounds on the information-theoretically optimal throughputs as a function of the channel parameters, the desired level of covertness, and the amount of shared key available. Further, these bounds match for a wide range of parameters of interest.
Message authentication is an interactive procedure that allows a legitimate sender Alice to send and authenticate a message M to a legitimate receiver Bob. To prevent the attacks from an adversary Eve, Alice and Bob usually share a secret key K. In this paper, we study a novel authentication framework as follows. Firstly, Alice sends a message M to Bob over a noiseless channel; Secondly, Alice generates an authentication tag with the message M and secret key K; Thirdly, Alice encodes the tag into a codeword Xn; Finally, Alice transmits the codeword Xn to Bob over a wiretap channel. This paper defines an authentication channel capacity under a fixed tag rate, and show that it equals to H(X|Z). Specifically, we prove that the authentication protocol proposed in Ref. [15] is capacity-achievable under our authentication model.
We study a keyless authentication problem in a new noisy model, where there is a discrete memoryless channel (DMC) W1from sender Alice to receiver Bob and a DMC W2from adversary Oscar to Bob. In addition, there is an insecure noiseless channel between Alice and Bob. Under this model, we characterize the condition under which an authentication from Alice to Bob is possible. We also construct a secure authentication protocol that has an authentication rate approaching infinity. Finally, we prove that the authentication capacity of a noninteractive authentication over binary symmetric channels is exactly 1. This is an interesting result as Shannon capacity of channel W1is strictly less than 1 while the noiseless channel is completely unreliable.
This work considers the two way wiretap channel in which two legitimate users, Alice and Bob, wish to exchange messages securely in the presence of a passive eavesdropper Eve. In the full duplex scenario, where each node can transmit and receive simultaneously, we obtain new achievable secrecy rate regions based on the idea of allowing the two users to jointly optimize their channel prefixing distributions and binning codebooks; in addition to key sharing. The new regions are shown to be strictly larger than the known ones for a wide class of discrete memoryless and Gaussian channels. In the half duplex case, where a user can only transmit or receive on any given degree of freedom, we introduce the idea of randomized scheduling and establish the significant gain it offers in terms of the achievable secrecy sum-rate. We further develop an experimental setup based on a IEEE 802.15.4-enabled sensor boards to validate our theoretical analysis. Using this testbed, it is shown that one can exploit the two way nature of the communication, via appropriately randomizing the transmit power levels and transmission schedule, to introduce significant ambiguity at a noiseless Eve. To the best of our knowledge, this is one of the first attempts aiming towards building practical secrecy protocols inspired by information theoretic principles.