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It is well-known that randomness is essential for secure cryptography. The randomness used in cryptographic primitives is not necessarily recoverable even by the party who can, e.g., decrypt or recover the underlying secret/message. Several cryptographic primitives that support randomness recovery have turned out useful in various applications. In this paper, we study randomness recoverable secret sharing schemes (RR-SSS), in both information-theoretic and computational settings and provide two results. First, we show that while every access structure admits a perfect RR-SSS, there are very simple access structures (e.g., in monotone AC 0 ) that do not admit efficient perfect (or even statistical) RR-SSS. Second, we show that the existence of efficient computational RR-SSS for certain access structures in monotone AC 0 implies the existence of one-way functions. This stands in sharp contrast to (non-RR) SSS schemes for which no such results are known. RR-SSS plays a key role in making advanced attributed-based encryption schemes randomness recoverable, which in turn have applications in the context of designated-verifier non-interactive zero knowledge. [ABSTRACT FROM AUTHOR]

Quantum key distribution (QKD) and post‐quantum cryptography (PQC) are the two counter measures against cryptographic attacks via quantum computing. While QKD offers information theoretic security but limited authentication scalability, PQC facilitates scalable authentication in high density networks but is not information theoretic secure. Therefore, an ideal quantum‐safe framework should efficiently leverage the complementarity of both techniques. However, despite growing efforts in integrating both, current realizations have focused on channel authentication, and a complete cryptosystem addressing both hybrid authentication and hybrid key exchange is yet to be demonstrated. Here, an authenticated hybrid key exchange protocol is introduced that incorporates PQC and QKD in a modular and information‐theoretic secure architecture. The quantum‐safe protocol is inherently resilient to catastrophic cryptographic failures and provides both forward and post‐compromise security. As proof‐of‐concept implementation, the cryptosystem on a QKD hardware prototype is integrated, with the QKD processing, PQC key exchange and secret state masking via physical unclonable functions (PUFs) all running on a single field programmable gate array (FPGA). This work paves the way for the deployment of versatile and modular quantum‐safe networks that exploit the complementarity of PQC and QKD. [ABSTRACT FROM AUTHOR]

Large matrix multiplications commonly take place in large-scale machine-learning applications. Often, the sheer size of these matrices prevent carrying out the multiplication at a single server. Therefore, these operations are typically offloaded to a distributed computing platform with a master server and a large amount of workers in the cloud, operating in parallel. For such distributed platforms, it has been recently shown that coding over the input data matrices can reduce the computational delay by introducing a tolerance against straggling workers, i.e., workers for which execution time significantly lags with respect to the average. In addition to exact recovery, we impose a security constraint on both matrices to be multiplied. Specifically, we assume that workers can collude and eavesdrop on the content of these matrices. For this problem, we introduce a new class of polynomial codes with fewer non-zero coefficients than the degree +1. We provide closed-form expressions for the recovery threshold and show that our construction improves the recovery threshold of existing schemes in the literature, in particular for larger matrix dimensions and a moderate to large number of colluding workers. In the absence of any security constraints, we show that our construction is optimal in terms of recovery threshold. [ABSTRACT FROM AUTHOR]

We extend the problem of secure source coding by considering a remote source whose noisy measurements are correlated random variables used for secure source reconstruction. The main additions to the problem are as follows: (1) all terminals noncausally observe a noisy measurement of the remote source; (2) a private key is available to all legitimate terminals; (3) the public communication link between the encoder and decoder is rate-limited; and (4) the secrecy leakage to the eavesdropper is measured with respect to the encoder input, whereas the privacy leakage is measured with respect to the remote source. Exact rate regions are characterized for a lossy source coding problem with a private key, remote source, and decoder side information under security, privacy, communication, and distortion constraints. By replacing the distortion constraint with a reliability constraint, we obtain the exact rate region for the lossless case as well. Furthermore, the lossy rate region for scalar discrete-time Gaussian sources and measurement channels is established. An achievable lossy rate region that can be numerically computed is also provided for binary-input multiple additive discrete-time Gaussian noise measurement channels. [ABSTRACT FROM AUTHOR]

In the robust secure aggregation problem, a server wishes to learn and only learn the sum of the inputs of a number of users while some users may drop out (i.e., may not respond). The identity of the dropped users is not known a priori and the server needs to securely recover the sum of the remaining surviving users. We consider the following minimal two-round model of secure aggregation. Over the first round, any set of no fewer than $U$ users out of $K$ users respond to the server and the server wants to learn the sum of the inputs of all responding users. The remaining users are viewed as dropped. Over the second round, any set of no fewer than $U$ users of the surviving users respond (i.e., dropouts are still possible over the second round) and from the information obtained from the surviving users over the two rounds, the server can decode the desired sum. The security constraint is that even if the server colludes with any $T$ users and the messages from the dropped users are received by the server (e.g., delayed packets), the server is not able to infer any additional information beyond the sum in the information theoretic sense. For this information theoretic secure aggregation problem, we characterize the optimal communication cost. When $U \leq T$ , secure aggregation is not feasible, and when $U > T$ , to securely compute one symbol of the sum, the minimum number of symbols sent from each user to the server is 1 over the first round, and $1/(U-T)$ over the second round. [ABSTRACT FROM AUTHOR]

Directional Modulation (DM) techniques provide wireless communication security against passive eavesdropping by means of specific physical layer characteristics. The original symbol constellations are transmitted along pre-specified spatial direction of legitimate users, while phase-amplitude distorted symbols are transmitted along the undesired directions of eavesdropper. In this paper, a comprehensive review of DM techniques and the most recent developments in this area are discussed. An analysis from three independent Physical Layer Security (PLS) viewpoints; communications, information-theoretic and cryptographic perspective is presented. Different performance metrics in literature are compared and the need for unified PLS approach is emphasized. As DM techniques constitute a relatively new class of PLS, there is no systematic organization of these techniques so far. This paper presents a classification framework for DM comprising of two main categories; angular (1D) and range-angular (2D) techniques. The former secures data along angular direction of physical space, while the latter provides security within certain range (distance) from the transmitter along desired angular direction. Further sub-categorization is based on the under-lying physical layer parameters exploited to achieve security, i.e. space, time, frequency, phase and polarization. The proposed framework is generic, flexible and extend-able to future research. In the end, limitations of existing techniques are pointed out and research directions are suggested. [ABSTRACT FROM AUTHOR]

We consider a transmitter and $K$ receivers, each of which shares a key variable with the transmitter. Through a noiseless broadcast channel, the transmitter wishes to send a common message $W$ securely to $N$ out of the $K$ receivers while the remaining $K-N$ receivers learn no information about $W$. We are interested in the maximum message rate, i.e., the maximum number of bits of $W$ that can be securely groupcast to the legitimate receivers per key block and the minimum broadcast bandwidth, i.e., the minimum number of bits of the broadcast information required to securely groupcast the message bits. We focus on the setting of combinatorial keys, where every subset of the $K$ receivers share an independent key of arbitrary size. Under this combinatorial key setting, the maximum message rate is characterized for the following scenarios - 1) $N=1$ or $N=K-1$ , i.e., secure unicast to 1 receiver with $K-1$ eavesdroppers or secure groupcast to $K-1$ receivers with 1 eavesdropper, 2) $N=2, K=4$ , i.e., secure groupcast to 2 out of 4 receivers, and 3) the symmetric setting where the key size for any subset of the same cardinality is equal for any $N,K$. Further, for the latter two cases, the minimum broadcast bandwidth for the maximum message rate is characterized. [ABSTRACT FROM AUTHOR]

In this paper, the role of secret key with finite rate is studied to enhance the secrecy performance of the system when users are operating in interference limited scenarios. To address this problem, a 2-user Gaussian Z-interference channel with secrecy constraint at the receiver is considered. The paper proposes novel achievable schemes, where the schemes differ from each other based on how the key has been used in the encoding process. The first achievable scheme uses a combination of key rate splitting, one-time pad, stochastic encoding and superposition coding. In this scheme, one part of the key is used for one-time pad and the remaining part of the key is used for stochastic encoding. The encoding is performed such that the receiver experiencing interference can decode some part of the interference without violating the secrecy constraint. As a special case of the derived result, one can obtain the secrecy rate region when the key is completely used for one-time pad or part of the stochastic encoding. The second scheme uses the shared key to encrypt the message using one-time pad and in contrast to the previous case no interference is decoded at the receiver. The paper also derives outer bound on the sum rate and secrecy rate. The main novelty of deriving outer bound lies in the selection of side information provided to the receiver and using the secrecy constraint. The derived outer bounds are found to be tight for certain channel conditions and rate of the key. The scaling behaviour of key rate is also explored for different schemes using the notion of secure generalized degrees of freedom. The optimality of different schemes are characterized for some specific cases. The developed results show the importance of key rate splitting in enhancing the secrecy performance of the system. [ABSTRACT FROM AUTHOR]

To overcome the limitations of QKD, post-quantum cryptography, and computational security-based cryptography protocols in this paper, an atmospheric turbulence-controlled cryptosystem is proposed. The proposed encryption scheme employs the traditional scheme to utilize the atmospheric turbulence as the common source of randomness only in the initialization stage to determine the common parameters to be used in the proposed encryption scheme. To overcome low secret-key rates of traditional scheme, dictated by the long coherence time Tc of turbulence channel, the proposed encryption scheme updates the parameters of gamma-gamma distribution, used to generate irradiance samples for cumulative distribution function-based determination of the key, every Tc seconds and as such the final key is shaped by the atmospheric turbulence channel. We also describe a scheme that randomly selects one of several available paths in which the simultaneously measured irradiance samples, after interleaving, are used to generate the raw key. The secret-key rates of the proposed schemes are orders of magnitude higher compared to corresponding traditional QKD and source type physical-layer security schemes and are comparable with the state-of-the-art optical communication data rates.

Security of QKD is guaranteed by the quantum mechanics laws rather than unproven assumptions employed in computational cryptography. Unfortunately, the secret-key rates are way too low and transmission distances are limited. The post-quantum cryptography (PQC) is proposed as an alternative to QKD. However, the PQC protocols are based on conjecture that there are no polynomial time algorithms to break the PQC protocols. To overcome key challenges of both post-quantum cryptography and QKD, we propose to use the QKD only in initialization stage to set-up corresponding cybersecurity protocols. The proposed concept is applied to both computational security and PQC protocols. The proposed QKD-enhanced cybersecurity protocols are tolerant to attacks initiated by quantum computers.

Large matrix multiplications commonly take place in large-scale machine-learning applications. Often, the sheer size of these matrices prevent carrying out the multiplication at a single server. Therefore, these operations are typically offloaded to a distributed computing platform with a master server and a large amount of workers in the cloud, operating in parallel. For such distributed platforms, it has been recently shown that coding over the input data matrices can reduce the computational delay by introducing a tolerance against straggling workers, i.e., workers for which execution time significantly lags with respect to the average. In addition to exact recovery, we impose a security constraint on both matrices to be multiplied. Specifically, we assume that workers can collude and eavesdrop on the content of these matrices. For this problem, we introduce a new class of polynomial codes with fewer non-zero coefficients than the degree +1. We provide closed-form expressions for the recovery threshold and show that our construction improves the recovery threshold of existing schemes in the literature, in particular for larger matrix dimensions and a moderate to large number of colluding workers. In the absence of any security constraints, we show that our construction is optimal in terms of recovery threshold.

We extend the problem of secure source coding by considering a remote source whose noisy measurements are correlated random variables used for secure source reconstruction. The main additions to the problem are as follows: (1) all terminals noncausally observe a noisy measurement of the remote source; (2) a private key is available to all legitimate terminals; (3) the public communication link between the encoder and decoder is rate-limited; and (4) the secrecy leakage to the eavesdropper is measured with respect to the encoder input, whereas the privacy leakage is measured with respect to the remote source. Exact rate regions are characterized for a lossy source coding problem with a private key, remote source, and decoder side information under security, privacy, communication, and distortion constraints. By replacing the distortion constraint with a reliability constraint, we obtain the exact rate region for the lossless case as well. Furthermore, the lossy rate region for scalar discrete-time Gaussian sources and measurement channels is established. An achievable lossy rate region that can be numerically computed is also provided for binary-input multiple additive discrete-time Gaussian noise measurement channels.

The design of lattice coset codes for wiretap channels is considered. Bounds on the eavesdropper’s correct decoding probability and information leakage are first revisited. From these bounds, it is explicit that both the information leakage and error probability are controlled by the average flatness factor of the eavesdropper’s lattice, which we further interpret geometrically. It is concluded that the minimization of the (average) flatness factor of the eavesdropper’s lattice leads to the study of well-rounded lattices, which are shown to be among the optimal in order to achieve these minima. Constructions of some well-rounded lattices are also provided. [ABSTRACT FROM AUTHOR]

Security of QKD is guaranteed by the quantum mechanics laws rather than unproven assumptions employed in computational cryptography. Unfortunately, the secret-key rates are way too low and transmission distances are limited. The post-quantum cryptography (PQC) is proposed as an alternative to QKD. However, the PQC protocols are based on conjecture that there are no polynomial time algorithms to break the PQC protocols. To overcome key challenges of both post-quantum cryptography and QKD, we propose to use the QKD only in initialization stage to set-up corresponding cybersecurity protocols. The proposed concept is applied to both computational security and PQC protocols. The proposed QKD-enhanced cybersecurity protocols are tolerant to attacks initiated by quantum computers. [ABSTRACT FROM AUTHOR]

To overcome the limitations of QKD, post-quantum cryptography, and computational security-based cryptography protocols in this paper, an atmospheric turbulence-controlled cryptosystem is proposed. The proposed encryption scheme employs the traditional scheme to utilize the atmospheric turbulence as the common source of randomness only in the initialization stage to determine the common parameters to be used in the proposed encryption scheme. To overcome low secret-key rates of traditional scheme, dictated by the long coherence time Tc of turbulence channel, the proposed encryption scheme updates the parameters of gamma-gamma distribution, used to generate irradiance samples for cumulative distribution function-based determination of the key, every Tc seconds and as such the final key is shaped by the atmospheric turbulence channel. We also describe a scheme that randomly selects one of several available paths in which the simultaneously measured irradiance samples, after interleaving, are used to generate the raw key. The secret-key rates of the proposed schemes are orders of magnitude higher compared to corresponding traditional QKD and source type physical-layer security schemes and are comparable with the state-of-the-art optical communication data rates. [ABSTRACT FROM AUTHOR]

Traditional security analysis of wiretap codes requires evaluation of equivocation in the asymptote as the code blocklength tends to infinity. Finite blocklength codes, however, require exact expressions for equivocation so as to allow for comparison of parameterized codes across different code constructions or within the same construction. In this letter, we present two exact equivocation expressions for coset coding over the wiretap channel model with binary erasure channels (BECs) for both the main channel and the eavesdropper’s channel. The expressions are functions of the algebraic structure of the binary wiretap codes, and they also hold for the special case when the main channel is noiseless. [ABSTRACT FROM AUTHOR]

Two legitimate parties, referred to as Alice and Bob, wish to generate secret keys from the wireless channel in the presence of an eavesdropper, referred to as Eve, in order to use such keys for encryption and decryption. In general, the secret key rate highly depends on the coherence time of the channel. In particular, a straightforward method of generating secret keys in static environments results in ultra-low rates. In order to resolve this problem, we introduce a low-complexity method called induced randomness. In this method, Alice and Bob independently generate local randomness to be used together with the uniqueness of the wireless channel coefficients in order to enable high-rate secret key generation. In this work, two scenarios are considered: first, when Alice and Bob share a direct communication channel, and second, when Alice and Bob do not have a direct link and communicate through an untrusted relay. After exchanging the induced randomness, post-processing is done by Alice and Bob to generate highly-correlated samples that are used for the key generation. Such samples are then converted into bits, disparities between the sequences generated by Alice and Bob are mitigated, and the resulting sequences are then hashed to compensate for the information leakage to the eavesdropper and to allow consistency checking of the generated key bit sequences. We utilize semantic security measures and information-theoretic inequalities to upper bound the probability of successful eavesdropping attack in terms of the mutual information measures that can be numerically computed. Given certain reasonable system parameters this bound is numerically evaluated to be $2^{-31}$ and $2^{-10.57}$ in the first and the second scenario, respectively. [ABSTRACT FROM AUTHOR]

Large matrix multiplications are central to large-scale machine learning applications. These operations are often carried out on a distributed computing platform with a master server and multiple workers in the cloud operating in parallel. For such distributed platforms, it has been recently shown that coding over the input data matrices can reduce the computational delay, yielding a trade-off between recovery threshold, i.e., the number of workers required to recover the matrix product, and communication load, i.e., the total amount of data to be downloaded from the workers. In this paper, in addition to exact recovery requirements, we impose security and privacy constraints on the data matrices, and study the recovery threshold as a function of the communication load. We first assume that both matrices contain private information and that workers can collude to eavesdrop on the content of these data matrices. For this problem, we introduce a novel class of secure codes, referred to as secure generalized PolyDot (SGPD) codes, that generalize state-of-the-art non-secure codes for matrix multiplication. SGPD codes allow a flexible trade-off between recovery threshold and communication load for a fixed maximum number of colluding workers while providing perfect secrecy for the two data matrices. We then study a connection between secure matrix multiplication and private information retrieval. We specifically assume that one of the data matrices is taken from a public set known to all the workers. In this setup, the identity of the matrix of interest should be kept private from the workers. For this model, we present a variant of generalized PolyDot codes that can guarantee both secrecy of one matrix and privacy for the identity of the other matrix for the case of no colluding servers. [ABSTRACT FROM AUTHOR]

Private simultaneous message (PSM) protocols were introduced by Feige, Kilian, and Naor (STOC '94) as a minimal non-interactive model for information theoretic three-party secure computation. While it is known that every function f : { 0 , 1 } k × { 0 , 1 } k → { 0 , 1 } admits a PSM protocol with exponential communication of 2 k / 2 (Beimel et al., TCC '14), the best known (non-explicit) lower-bound is 3 k - O (1) bits. To prove this lower-bound, FKN identified a set of simple requirements, showed that any function that satisfies these requirements is subject to the 3 k - O (1) lower-bound, and proved that a random function is likely to satisfy the requirements. We revisit the FKN lower-bound and prove the following results: (Counterexample) We construct a function that satisfies the FKN requirements but has a PSM protocol with communication of 2 k + O (1) bits, revealing a gap in the FKN proof. (PSM lower-bounds) We show that by imposing additional requirements, the FKN argument can be fixed leading to a 3 k - O (log k) lower-bound for a random function. We also get a similar lower-bound for a function that can be computed by a polynomial-size circuit (or even polynomial-time Turing machine under standard complexity-theoretic assumptions). This yields the first non-trivial lower-bound for an explicit Boolean function partially resolving an open problem of Data, Prabhakaran, and Prabhakaran (Crypto '14, IEEE Information Theory '16). We further extend these results to the setting of imperfect PSM protocols which may have small correctness or privacy error. (CDS lower-bounds) We show that the original FKN argument applies (as is) to some weak form of PSM protocols which are strongly related to the setting of Conditional Disclosure of Secrets (CDS). This connection yields a simple combinatorial criterion for establishing linear Ω (k) -bit CDS lower-bounds. As a corollary, we settle the complexity of the inner-product predicate resolving an open problem of Gay, Kerenidis, and Wee (Crypto '15). [ABSTRACT FROM AUTHOR]

We consider compound multi-input multi-output (MIMO) wiretap channels where minimal channel state information at the transmitter (CSIT) is assumed. Code construction is given for the special case of isotropic mutual information, which serves as a conservative strategy for general cases. Using the flatness factor for MIMO channels, we propose lattice codes universally achieving the secrecy capacity of compound MIMO wiretap channels up to a constant gap (measured in nats) that is equal to the number of transmit antennas. The proposed approach improves upon existing works on secrecy coding for MIMO wiretap channels from an error probability perspective, and establishes information theoretic security (in fact semantic security). We also give an algebraic construction to reduce the code design complexity, as well as the decoding complexity of the legitimate receiver. Thanks to the algebraic structures of number fields and division algebras, our code construction for compound MIMO wiretap channels can be reduced to that for Gaussian wiretap channels, up to some additional gap to secrecy capacity. [ABSTRACT FROM AUTHOR]

In many communication channels, secrecy constraints usually incur a penalty in capacity, as well as generalized degrees-of-freedom (GDoF). In this paper, we show an interesting observation that adding a helper can totally remove the penalty in sum GDoF for a two-user symmetric Gaussian interference channel. For the interference channel where each transmitter sends a message to an intended receiver without secrecy constraints, the sum GDoF is a well-known “W” curve, characterized by Etkin–Tse–Wang in 2008. If the secrecy constraints are imposed on this interference channel, where the message of each transmitter must be secure from the unintended receiver (eavesdropper), then a GDoF penalty is incurred and the secure sum GDoF is reduced to a modified “W” curve, derived by Chen recently. In this paper, we show that, by adding a helper into this interference channel with secrecy constraints, the secure sum GDoF turns out to be a “W” curve, which is the same as the sum GDoF of the setting without secrecy constraints. The proposed scheme is based on the cooperative jamming and a careful signal design such that the jamming signal of the helper is aligned at a specific direction and power level with the information signals of the transmitters, which allows us to totally remove the penalty in GDoF due to the secrecy constraints. Furthermore, the estimation approaches of noise removal and signal separation due to the rational independence are used in the secure rate analysis. [ABSTRACT FROM AUTHOR]

The two-terminal key agreement problem with biometric or physical identifiers is considered. Two linear code constructions based on Wyner–Ziv coding are developed. The first construction uses random linear codes and achieves all points of the key-leakage-storage regions of the generated-secret and chosen-secret models. The second construction uses nested polar codes for vector quantization during enrollment and for error correction during reconstruction. The simulation results show that the nested polar codes achieve privacy leakage and storage rates that improve on existing code designs. One proposed code achieves a rate tuple that cannot be achieved by existing methods. [ABSTRACT FROM AUTHOR]

In this paper, we introduce the notion of plausible deniability in an information theoretic framework. We consider a scenario where an entity that eavesdrops through a broadcast channel summons one of the parties in a communication protocol to reveal their message (or signal vector). It is desirable that the summoned party has enough freedom to produce a fake output that is likely plausible given the eavesdropper’s observation. We examine three variants of this problem—message deniability, transmitter deniability, and receiver deniability. In the first setting, the message sender is summoned to produce the sent message. Similarly, in the second and third settings, the transmitter and the receiver are required to produce the transmitted codeword and the received vector, respectively. For each of these settings, we examine the maximum communication rate that allows a given minimum rate of plausible fake outputs. First, for the message deniability problem, we fully characterize the capacity region for general broadcast channels. Next, for the transmitter deniability problem, we give an achievable region for general broadcast channels by fully characterizing the set of rate pairs’ achievable using deterministic coding schemes. Finally, for the receiver deniability problem, we give an achievable rate region for physically degraded broadcast channels. [ABSTRACT FROM AUTHOR]

In this paper, we study a diamond-relay channel where the source is connected to $M$ relays through orthogonal links and the relays transmit to the destination over a wireless multiple-access channel in the presence of an eavesdropper. The eavesdropper not only observes the relay transmissions through another multiple-access channel but also observes a certain number of source-relay links. The legitimate terminals know neither the eavesdropper’s channel state information nor the location of source-relay links revealed to the eavesdropper except the total number of such links. For this wiretapped diamond-relay channel, we establish the optimal secure d.o.f. In the achievability part, our proposed scheme uses the source-relay links to transmit a judiciously constructed combination of message symbols, artificial noise symbols, and fictitious message symbols associated with secure network coding. The relays use a combination of beamforming and interference alignment in their transmission scheme. For the converse part, we take a genie-aided approach assuming that the location of wiretapped links is known. [ABSTRACT FROM AUTHOR]

Despite several works on secrecy coding for fading and MIMO wiretap channels from an error probability perspective, the construction of information-theoretically secure codes over such channels remains an open problem. In this paper, we consider a fading wiretap channel model where the transmitter has only partial statistical channel state information. Our channel model includes static channels, i.i.d. block fading channels, and ergodic stationary fading with fast decay of large deviations for the eavesdropper’s channel. We extend the flatness factor criterion from the Gaussian wiretap channel to fading and MIMO wiretap channels, and establish a simple design criterion where the normalized product distance/minimum determinant of the lattice and its dual should be maximized simultaneously. Moreover, we propose concrete lattice codes satisfying this design criterion, which are built from algebraic number fields with constant root discriminant in the single-antenna case, and from division algebras centered at such number fields in the multiple-antenna case. The proposed lattice codes achieve strong secrecy and semantic security for all rates $R< C_{b}-C_{e}-\kappa $ , where $C_{b}$ and $C_{e}$ are Bob and Eve’s channel capacities, respectively, and $\kappa $ is an explicit constant gap. Furthermore, these codes are almost universal in the sense that a fixed code is good for secrecy for a wide range of fading models. Finally, we consider a compound wiretap model with a more restricted uncertainty set, and show that rates $R< \bar {C}_{b}-\bar {C}_{e}-\kappa $ are achievable, where $\bar {C}_{b}$ is a lower bound for Bob’s capacity and $\bar {C}_{e}$ is an upper bound for Eve’s capacity for all the channels in the set. [ABSTRACT FROM AUTHOR]

Private information retrieval (PIR) is a database query protocol that provides user privacy in that the user can learn a particular entry of the database of his interest but his query would be hidden from the data centre. Symmetric private information retrieval (SPIR) takes PIR further by additionally offering database privacy, where the user cannot learn any additional entries of the database. Unconditionally secure SPIR solutions with multiple databases are known classically, but are unrealistic because they require long shared secret keys between the parties for secure communication and shared randomness in the protocol. Here, we propose using quantum key distribution (QKD) instead for a practical implementation, which can realise both the secure communication and shared randomness requirements. We prove that QKD maintains the security of the SPIR protocol and that it is also secure against any external eavesdropper. We also show how such a classical-quantum system could be implemented practically, using the example of a two-database SPIR protocol with keys generated by measurement device-independent QKD. Through key rate calculations, we show that such an implementation is feasible at the metropolitan level with current QKD technology.

• Secret image sharing preserves secret images, but region privacy is not attained • Regional secret sharing can provide region privacy • It is efficient, practical and information theoretically secure. Secret image sharing (SIS), a tool capable of distributing a private image among certain number of shareholders, ensures both authorized recovery and unauthorized forbidding of the same. However, usually, in SIS every pixel is treated with equal weight. This is a hindrance in case of partial query to the original secret image, where usual SIS might over-inform the querier. To prevent this over-spilling of information, we introduce, in this work, the notion of Regional Secret Sharing , where access to a special region is not possible in general, unless an essential participant submits his shadow. We formally define (t , k , n) -Regional secret image sharing ((t , k , n) -RSIS) and provide a construction for the same using polynomial based secret image sharing. Our construction which is done over a finite field is completely lossless. We also formally prove the protocol's behaviour in different cases of authorized access and unauthorized access. Moreover, we support our constructions with sufficient experimental results. This is the first usage of the notion of region in secret image sharing. Our construction is information theoretically secure, meaning we do not assume any computational assumptions for the adversary, in the semi-honest model and it does not require any preprocessing unlike most SIS schemes, making the scheme efficient as well. [ABSTRACT FROM AUTHOR]

We introduce two new Kirchhoff-law-Johnson-noise (KLJN) secure key distribution schemes which are generalizations of the original KLJN scheme. The first of these, the Random-Resistor (RR-) KLJN scheme, uses random resistors with values chosen from a quasi-continuum set. It is well-known since the creation of the KLJN concept that such a system could work in cryptography, because Alice and Bob can calculate the unknown resistance value from measurements, but the RR-KLJN system has not been addressed in prior publications since it was considered impractical. The reason for discussing it now is the second scheme, the Random Resistor Random Temperature (RRRT-) KLJN key exchange, inspired by a recent paper of Vadai, Mingesz and Gingl, wherein security was shown to be maintained at non-zero power flow. In the RRRT-KLJN secure key exchange scheme, both the resistances and their temperatures are continuum random variables. We prove that the security of the RRRT-KLJN scheme can prevail at a non-zero power flow, and thus the physical law guaranteeing security is not the Second Law of Thermodynamics but the Fluctuation-Dissipation Theorem. Alice and Bob know their own resistances and temperatures and can calculate the resistance and temperature values at the other end of the communication channel from measured voltage, current and power-flow data in the wire. However, Eve cannot determine these values because, for her, there are four unknown quantities while she can set up only three equations. The RRRT-KLJN scheme has several advantages and makes all former attacks on the KLJN scheme invalid or incomplete.

Identity authentication is the process of verifying users’ validity. Unlike classical key-based authentications, which are built on noiseless channels, this paper introduces a general analysis and design framework for identity authentication over noisy channels. Specifically, the authentication scenarios of single time and multiple times are investigated. For each scenario, the lower bound on the opponent’s success probability is derived, and it is smaller than the classical identity authentication’s. In addition, it can remain the same, even if the secret key is reused. Remarkably, the Cartesian authentication code proves to be helpful for hiding the secret key to maximize the secrecy performance. Finally, we show a potential application of this authentication technique.

Different security notions of secret sharing schemes have been proposed by different information measures. Entropies, such as Shannon entropy and min entropy, are frequently used in the setting security notions for secret sharing schemes. Different to the entropies, Kolmogorov complexity was also defined and used in study the security of individual instances for secret sharing schemes. This paper is concerned with these security notions for secret sharing schemes defined by the variational measures, including Shannon entropy, guessing probability, min entropy and Kolmogorov complexity.

A cellular transformation of bipolar fuzzy sets to quantum intelligence (QI) machinery is presented based on an axiomatic formulation of equilibrium-based business intelligence (EBBI) and information conservational quantum-fuzzy cryptography (ICQFC). It is proven that any active bipolar cognitive map can be normalized to a bipolar quantum-fuzzy cognitive map—the logical equivalent of an information conservational bipolar quantum-fuzzy logic gate for equilibrium-based quantum cellular rebalancing. Such rebalancing leads to EBBI and ICQFC—an unexpected combination with unexpected synergy. Applicability of one EBBI algorithm and two ICQFC algorithms are illustrated. Information theoretic security and scalability of ICQFC are proved as a computational intelligence testbed for postquantum cryptography. It is argued that, while the illogical aspect of quantum mechanics prevents quantum computing from lending itself as an analytical paradigm, EBBI and ICQFC constitute a cellular transformation of bipolar fuzzy sets to high precision QI machinery—an equilibrium-based analytical paradigm for ubiquitous quantum modeling and quantum-digital compatible computing. A QI architecture is drafted. A QI transfer protocol is illustrated with ICQFC for EBBI. QI is, thus, distinguished by its ubiquitous, analytical, transferable, and quantum-digital compatible properties. It is asserted that QI as the most generic genre of intelligence underpins artificial and biological intelligence with mathematical, philosophical, and scientific distinctions. It is expected that through QI the research field of fuzzy sets and systems is destined to advance to the forefront of modern science including but not limited to brain science and quantum information science. [ABSTRACT FROM PUBLISHER]

Recent work by Maddah-Ali and Niesen (2014) introduced coded caching which demonstrated the benefits of joint design of storage and transmission policies in content delivery networks. They studied a setup where a server communicates with a set of users, each equipped with a local cache, over a shared error-free link and proposed an order-optimal caching and delivery scheme. In this paper, we introduce the problem of private coded caching where we impose the additional constraint that no user learns any information about the contents of the files it did not request from what is stored in its cache and the server transmissions. We propose a feasible scheme for this setting and demonstrate its order-optimality by deriving information-theoretic lower bounds. [ABSTRACT FROM PUBLISHER]