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arXiv:1211.4976

Channel Independent Cryptographic Key Distribution

Benjamin T. H. Varcoe

Published Nov 21, 2012• 0 citations
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Abstract

This paper presents a method of cryptographic key distribution using an `artificially' noisy channel. This is an important development because, while it is known that a noisy channel can be used to generate unconditional secrecy, there are many circumstances in which it is not possible to have a noisy information exchange, such as in error corrected communication stacks. It is shown that two legitimate parties can simulate a noisy channel by adding local noise onto the communication and that the simulated channel has a secrecy capacity even if the underlying channel does not. A derivation of the secrecy conditions is presented along with numerical simulations of the channel function to show that key exchange is feasible.

DOI
10.48550/arxiv.1211.4976

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This paper presents a method of cryptographic key distribution using an `artificially' noisy channel. This is an important development because, while it is known that a noisy channel can be used to generate unconditional secrecy, there are many circumstances in which it is not possible to have a noisy information exchange, such as in error corrected communication stacks. It is shown that two legitimate parties can simulate a noisy channel by adding local noise onto the communication and that the simulated channel has a secrecy capacity even if the underlying channel does not. A derivation of the secrecy conditions is presented along with numerical simulations of the channel function to show that key exchange is feasible.
In Chapter 3, we considered the transmission of information over a noisy broadcast channel subject to reliability and security constraints; we showed that appropriate coding schemes can exploit the presence of noise to confuse the eavesdropper and guarantee some amount of information-theoretic security. It is important to note that the wiretap channel model assumes that all communications occur over the channel, hence communications are inherently rate-limited and one-way. Consequently, the results obtained do not fully capture the role of noise for secrecy; in particular, for situations in which the secrecy capacity is zero, it is not entirely clear whether this stems from the lack of any “physical advantage” over the eavesdropper or the restrictions imposed on the communication schemes. The objective of this chapter is to study more precisely the fundamental role of noise in information-theoretic security. Instead of studying how we can communicate messages securely over a noisy channel, we now analyze how much secrecy we can extract from the noise itself in the form of a secret key. Specifically, we assume that the legitimate parties and the eavesdropper observe the realizations of correlated random variables and that the legitimate parties attempt to agree on a secret key unknown to the eavesdropper. To isolate the role played by noise, we remove restrictions on communication schemes and we assume that the legitimate parties can distill their key by communicating over a two-way, public, noiseless , and authenticated channel at no cost.
Current security techniques can be implemented either by requiring a secret key exchange or depending on assumptions about the communication channels. In this paper, we show that, by using a physical layer technique known as artificial noise, it is feasible to protect secret data without any form of secret key exchange and any restriction on the communication channels. Specifically, we analyze how the artificial noise can achieve practical secrecy. By treating the artificial noise as an unshared one-time pad secret key, we show that the proposed scheme also achieves Shannon's perfect secrecy. Moreover, we show that achieving perfect secrecy is much easier than ensuring non-zero secrecy capacity, especially when the eavesdropper has more antennas than the transmitter. Focusing on the practical applications, we show that practical secrecy and strong secrecy can be guaranteed even if the eavesdropper attempts to remove the artificial noise. We finally show the connections between traditional cryptography and physical layer security.
It is known that noise on communication channels can be a powerful resource for certain cryptographic purposes, basically by utilizing the randomness to ensure the secrecy. In this paper, we study information theoretically secure key agreement through the use of the additive white Gaussian noise channel and public discussion. We present a protocol for key agreement that defines the computation and communications between the two communicating parties to share a common secret information, about which negligible amount of information is revealed to other third parties. We discuss the signal design, secrecy and the achievable rate of the protocol.
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Shannon-theoretic secret key generation by several parties is considered for models in which a secure noisy channel with one input terminal and multiple output terminals and a public noiseless channel of unlimited capacity are available for accomplishing this goal. The secret key is generated for a setAAAof terminals of the noisy channel, with the remaining terminals (if any) cooperating in this task through their public communication. Single-letter characterizations of secrecy capacities are obtained for models in which secrecy is required from an eavesdropper that observes only the public communication and perhaps also a set of terminals disjoint fromAAA. These capacities are shown to be achievable with noninteractive public communication, the channel input terminal sending no public message and each output terminal sending at most one public message, not using randomization. Moreover, when the input terminal belongs to the setAAA, it can generate the secret key at the outset and transmit it over the noisy channel, suitably encoded, whereupon the output terminals inAAAsecurely recover this key using public communication as above. For models in which the eavesdropper also possesses side information that is not available to any of the terminals cooperating in secrecy generation, an upper bound for the secrecy capacity and a sufficient condition for its tightness are given.