Information security schemes based on radio propagation property such as secret key agreement and secret data transmission have attracted attention in the current wireless community. For the secret key agreement from common information, a general formula of the secret key capacity is given, but a specific formula of secret key capacity has not present for secret key agreement from Gaussian correlated information, which is typical case in wireless channels. This paper deals with the theoretical analysis on secret key capacity for the mobile communication channel model. The analysis result shows that the upper band of secret key capacity is given with conditional mutual information and that the formulas of upper and lower bands are expressed as functions of the signal-to-noise power ratio and the noise power ratio of eavesdropper to legitimate user. The analysis result also shows that secret key capacity can approximately be given by conditional mutual information in the case that noise power ratio of eavesdropper to legitimate user is large.
Information security schemes based on radio propagation property such as secret key agreement and secret data transmission have attracted attention in the current wireless community. For the secret key agreement from common information, a general formula of the secret key capacity is given, but a specific formula of secret key capacity has not present for secret key agreement from Gaussian correlated information, which is typical case in wireless channels. This paper deals with the theoretical analysis on secret key capacity for the mobile communication channel model. The analysis result shows that the upper band of secret key capacity is given with conditional mutual information and that the formulas of upper and lower bands are expressed as functions of the signal-to-noise power ratio and the noise power ratio of eavesdropper to legitimate user. The analysis result also shows that secret key capacity can approximately be given by conditional mutual information in the case that noise power ratio of eavesdropper to legitimate user is large.
Secret key agreement based on radio propagation characteristics attracts attention as a kind of the wireless physical layer security recently. There are few studies of group secret key agreement in this field, but there is a method to notify of the difference between the series of RSS. However, the conventional method has a problem in derivation of theoretical expression of the secret key capacity. This paper deals with a close numerical formula of upper and lower limit of the secret key capacity to be given in mutual information. This paper derives new theoretical expression of the secret key capacity that is a function of the SN ratio by new theoretical analysis for the mutual information. As a result, numerical computation shows that the upper limit of the secret key capacity accords with the lower limit in high SN ratio. Numerical computation also shows that leakage information increases with increase of the number of the terminals. Furthermore, the result of the computer simulation shows validity of theoretical expression.
Secret key agreement based on radio propagation characteristics attracts attention as a kind of the wireless physical layer security recently. As one field, there is group secret key agreement to notify of the difference between the series of RSS in star and chain connection system. However, the conventional method has a problem in derivation of theoretical expression of the secret key capacity. This paper deals with a close numerical formula of upper and lower limit of the secret key capacity to be given in mutual information for chain connection systems. This paper derives new theoretical expression of the secret key capacity that is a function of the SN ratio by new theoretical analysis for the mutual information. As a result, numerical computation shows that the upper limit of the secret key capacity accords with the lower limit in high SN ratio. In addition, the simulation results show validity of theoretical expression because the simulation results accord with theoretical characteristics well.
Secret key agreement based on radio propagation characteristics attracts attention as a kind of the wireless physical layer security. However, there are few studies on drop of the secret key capacity by multiple spot eavesdropping. This paper derived theoretical formula of the secret key capacity in secret key agreement based on the complex channel coefficient. This paper also derived theoretical formula of the leakage information by multiple spot eavesdropping and showed that leakage information increased with the increase of the eavesdropping spot number. Validity of these theoretical formulas was confirmed by computer simulation. Then, this paper calculated the coefficient of correlation of the channel coefficient in the simple propagation environment and evaluated security of secret key agreement by calculating leakage information for multiple spot eavesdropping.
Wireless communication is riskier than wired communication due to eavesdrop by unauthorized stations. To deal with this problem, public key cryptosystem and common key cryptosystem are used in general. In contrast, key agreement schemes based on information-theoretically security attract attention. One example is a secret key agreement scheme based on radio wave propagation characteristics. This technique uses channel reciprocity and location dependency of radio wave propagation. Most of the secret key agreement schemes generate keys by scalar quantization. However, secret keys generated by scalar quantization occur key disagreement in higher probability than these by vector quantization. A general quantizer selection scheme selects a quantizer with minimum key disagreement between two authorized stations. An eavesdropper is able to generate keys with this quantizer more easily. This paper assumes correlated MIMO channel, and proposed the quantizer utilizing correlation between authorized stations as key information and the quantizer selection scheme taking key entropies leak to eavesdroppers into consideration. This scheme that reduces information leaks to eavesdropper maintaining key disagreement probability between authorized stations.
Fundamental limits of secret-key agreement over reciprocal wireless channels are investigated. We consider a two-way block-fading channel where the channel gains in the forward and reverse links between the legitimate terminals are correlated. The channel gains between the legitimate terminals are not revealed to any terminal, whereas the channel gains of the eavesdropper are revealed to the eavesdropper. We propose a two-phase transmission scheme, that reserves a certain portion of each coherence block for channel estimation, and the remainder of the coherence block for correlated source generation. The resulting secret-key involves contributions of both channel sequences and source sequences, with the contribution of the latter becoming dominant as the coherence period increases. We also establish an upper bound on the secret-key capacity, which has a form structurally similar to the lower bound. Our upper and lower bounds coincide in the limit of high signal-to-noise-ratio (SNR) and large coherence period, thus establishing the secret-key agreement capacity in this asymptotic regime. Numerical results indicate that the proposed scheme achieves significant gains over training-only schemes, even for moderate SNR and small coherence periods, thus implying the necessity of randomness-sharing in practical secret-key generation systems.
The aim of information-theoretic secrecy is to ensure that an eavesdropper who listens to the wireless transmission of a message can only collect an arbitrarily small number of information bits about this message. In contrast to cryptography, there are no assumptions on the computational power of the eavesdropper. Information-theoretically secret communication has been studied for many particular wireless network topologies. In the main part of this thesis, we consider such communication for arbitrary acyclic wireless network topologies. We provide lower and upper bounds on the strong perfect secrecy capacity for the case when the channels of the network are either Gaussian or deterministic. These results are based on the recent understanding of the capacity of wireless networks (without secrecy constraints) by Avestimehr, Diggavi and Tse. As a side result, we give inner and outer bounds on the capacity region for the multisource problem in arbitrary wireless networks with Gaussian or deterministic signal interaction. For linear deterministic signal interaction, we find the exact capacity region. For Gaussian signal interaction, we are able to bound the gap between the two bounds on the capacity region. This gap depends only on the network topology, but not on the signal-to-noise ratio (SNR), which leads to an approximation of the capacity region for the high SNR regime. We further consider a particular network topology, called the fan-network, in which we assume that an eavesdropper has physical access to every node in a subset of the relay nodes. We give a general upper bound on the perfect secrecy capacity, and we characterize the perfect secrecy capacity for two special cases. In the second part of the thesis, we consider interactive secrecy, i.e., secrecy in the presence of a public feedback link from the destination to the source. We focus on the problem of secret key generation rather than secret communication. The benefit of public discussion for secret key generation in a broadcast channel was first shown by Maurer. We extend his ideas to a relay network called the line network, leading to a lower bound on the strongly secret key capacity for this network topology. Finally, we introduce a new channel coding setup called the interference-multiple access (IMA) channel. This channel is a variant of the interference channel where one of the receivers is required to decode the messages from both transmitters. We derive an inner bound on the capacity region of the IMA channel, as well as an outer bound for the so-called structured IMA channel. In a semi-deterministic version of the structured IMA channel, the bounds match, providing a characterization of the capacity region. In the Gaussian case, we obtain a 1 bit-approximation of the capacity region. We also show an inner bound on the equivocation-capacity region for the IMA channel, where we require that part of the private message for one receiver is kept information-theoretically secret from the other receiver.