Fundamental Limits of Covert Bit Insertion in Packets

Network flow fingerprinting can be used to de-anonymize communications on anonymity systems such as Tor by linking the ingress and egress segments of anonymized connections. Assume Alice and Bob have access to the input and the output links of an anonymous network, respectively, and they wish to collaboratively reveal the connections between the input and the output links without being detected by Willie who protects the network. Alice generates a codebook of fingerprints, where each fingerprint corresponds to a unique sequence of interpacket delays and shares it only with Bob. For each input flow, she selects a fingerprint from the codebook and embeds it in the flow, i.e., changes the packet timings of the flow to follow the packet timings suggested by the fingerprint, and Bob extracts the fingerprints from the output flows. We model the network as parallel M/M/1 queues where each queue is shared by a flow from Alice to Bob and other flows independent of the flow from Alice to Bob. The timings of the flows are governed by independent Poisson point processes. Assuming all input flows have equal rates and that Bob observes only flows with fingerprints, we first present two scenarios: 1) Alice fingerprints all the flows; 2) Alice fingerprints a subset of the flows, unknown to Willie. Then, we extend the construction and analysis to the case where flow rates are arbitrary as well as the case where not all the flows that Bob observes have a fingerprint. For each scenario, we derive the number of flows that Alice can fingerprint and Bob can trace by fingerprinting.

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“…Consequently, by (4), (32) and (33), P f ≤ ζ for all ζ > 0, and thus Alice and Bob's fingerprinting is reliable.…”

Section: Extension To Arbitrary Ratesmentioning

confidence: 94%

“…Similar to the definition of covertness [28]- [32], we define invisibility [1]: the probability of the failure event satisfies P f ≤ ζ as T → ∞. We term ζ the reliability parameter.…”

Section: B Definitionsmentioning

confidence: 99%

Fundamental Limits of Invisible Flow Fingerprinting

Soltani

Goeckel

Towsley

et al. 2020

IEEE Trans.Inform.Forensic Secur.

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“…Similar to the definition of covertness in [1], [2], [16]- [18], [67], [68], and invisibility in [69], [70], we define covertness: We present results under the assumption that P(H 0 ) = P(H 1 ) = 1/2. However, this results in covertness for the general case [71, Appendix A].…”

Section: B Definitionsmentioning

confidence: 99%

“…Another way to communicate covertly on a packet channel is bit insertion, where Alice inserts bits in a subset of the packets [71]. This technique requires that packets have available space in their payload and a minimum of one bit in their header.…”

Section: Higher Throughput Via Timing Channel and Bit Insertionmentioning

confidence: 99%

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Fundamental Limits of Covert Packet Insertion

Soltani

Goeckel

Towsley

et al. 2020

IEEE Trans. Commun.

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Covert communication conceals the existence of the transmission from a watchful adversary. We consider the fundamental limits for covert communications via packet insertion over packet channels whose packet timings are governed by a renewal process of rate λ. Authorized transmitter Jack sends packets to authorized receiver Steve, and covert transmitter Alice wishes to transmit packets to covert receiver Bob without being detected by watchful adversary Willie. Willie cannot authenticate the source of the packets. Hence, he looks for statistical anomalies in the packet stream from Jack to Steve to attempt detection of unauthorized packet insertion. First, we consider a special case where the packet timings are governed by a Poisson process and we show that Alice can covertly insert O( √ λT ) packets for Bob in a time interval of length T ; conversely, if Alice inserts ω( √ λT ), she will be detected by Willie with high probability. Then, we extend our results to general renewal channels and show that in a stream of N packets transmitted by Jack, Alice can covertly insert O( √ N ) packets; if she inserts ω( √ N ) packets, she will be detected by Willie with high probability. [56]-[62] by leveraging information-theoretic analysis and the use of various coding techniques [40], [63], [64]. In particular, Anantharam and Verdu [65] derived the Shannon capacity of the timing channel with a single-server queue, and Dunn [66] analyzed the secrecy capacity of such a system. Per above, here we take a fundamental approach analogous to [12]-[23], but turn our attention to covert communication over wired channels in which communication takes place through packet transmissions.Specifically, we consider the scenario shown in Fig. 1. Authorized transmitter Jack sends packets to authorized receiver Steve. Assume that Alice wishes to transmit data covertly to Bob on this channel in the presence of an adversary, Willie, who is monitoring the channel. Willie can be in one of the two locations, either between Alice and Bob (Setting 1), or between Bob and Steve (Setting 2). Alice and Bob know that Willie is located at one or the other of these two places; however, they do not know which place he is located at. We assume Willie cannot authenticate the source of the packets (e.g., whether they are sent by Jack or not). However, he knows the statistical model of the timings of the packets transmitted by Jack. Alice can buffer and release Jack's packets and insert her own packets.Also, Bob can authenticate packets, remove the ones originally inserted by Alice, and buffer and release Jack's packets. We assume Alice can only send information to Bob by inserting her own packets into the channel, since she is not allowed to share a secret codebook with Bob and thus she is not able to send covert messages to Bob via packet timings; i.e., altering the timing of the packets according to a shared codebook, to embed information in inter-packet delays (IPDs) [65]. In addition, transmission of information through packet timings is sensitive to natural ...

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Covert Communication with Unknown Code at the Warden

Tahmasbi¹,

Bloch²

2019

2019 57th Annual Allerton Conference on Communication, Control, and Computing (Allerton)

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Fundamental Limits of Covert Bit Insertion in Packets

Cited by 3 publications

References 40 publications

Fundamental Limits of Invisible Flow Fingerprinting

Fundamental Limits of Invisible Flow Fingerprinting

Fundamental Limits of Covert Packet Insertion

Covert Communication with Unknown Code at the Warden

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