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In the initial stage of the quantum Internet, most of the practical quantum networks have been deployed relying on diverse individual quantum key distribution (QKD) protocols. However, this single-protocol paradigm cannot fulfill the heterogeneous requirements of the users, hence market-penetration of quantum networks is limited. Given the recent advances in QKD protocols, the next generation quantum networks are expected to support both legacy and emerging QKD protocols. However, the evolution from single-protocol to multi-protocol quantum networks poses numerous challenging problems. As a remedy, we conceive a practical protocol translation framework for supporting this migration from single-protocol to large-scale multi-protocol quantum networks. Furthermore, we propose a programmable multi-functional relay node architecture for harmonizing the components of a suitable relay node. A pair of protocol translation policies are presented for meeting the challenging security requirements of migration requests, which are compared to the single-protocol-based migration solutions both in terms of the translation success probability attained (i.e., the proportion of migration requests with successful protocol translation), and the average relaying risk probability encountered (i.e., the mean of the relaying risk probabilities of end-to-end key negotiation in a quantum network). Finally, we highlight a suite of open problems in both quantum secure direct communication and quantum teleportation for research into future multi-protocol quantum networks. [ABSTRACT FROM AUTHOR]

Mobile terminals have been widely used in the communication applications (e.g., vehicular network, e-Health, smart grid and e-Commerce) as they can obtain all kinds of services and upload data for users anytime and anywhere. With the number of users increasing dramatically and user demands diversifying, multi-server architecture was proposed to solve issues on lack of service resources that single-server architecture remains. However, multi-server architecture faces a series of challenges in applications, such as security and authentication efficiency requirements. Thus, many authenticated key agreement (AKA) protocols are presented, yet most of them require unacceptable computation and communication overhead, which is inefficient indeed. In this paper, we propose an adaptive secure handover authenticated key agreement protocol for multi-server architecture. Specifically, broadcast mechanism is utilized to assist users to select appropriate service providers with the lowest cost. Users can realize efficient handover authentication with multiple servers in the proposed scheme, that is, after completing initial authentication, users can switch to other servers and complete authentication through simple operations. Security analysis shows the proposed protocol can meet all security requirements and compared with other relevant protocols, it greatly reduces the computation and communication overhead. In addition, the above advantages grow significantly as the number of servers to be authenticated increases. [ABSTRACT FROM AUTHOR]

Vehicular ad hoc networks (VANETs) are vulnerable to many kinds of security attacks, so it is necessary to design an authenticated key agreement (AKA) scheme for securing communication channels in VANETs. Existing AKA schemes in VANETs have not provided an efficient and secure method to secure V2V and V2I communications simultaneously while meeting the necessary security and privacy requirements. Further, few key updating mechanisms, which are secure, conditional privacy-preserving, practical, and lightweight, exist in current VANETs AKA schemes. In this paper, we propose a proven secure AKA scheme for securing V2V and V2I communications in VANETs, which can be divided into two parts. The first part is a three-party authentication process in which vehicles, road side unit (RSU), and trust authority (TA) authenticate each other. The second part is the key agreement process, which is used in the key generation and updating processes. For this phase, we design a tree-based key agreement algorithm that considers two scenarios, i.e., the joining of an authenticated vehicle and the leaving of the vehicle. The formal security proof and the security analysis show that our proposed scheme satisfies session key security and the necessary security requirements in VANETs, respectively. The performance analysis demonstrates that our proposed scheme has an advantage over several representative AKA schemes in VANETs. [ABSTRACT FROM AUTHOR]

As a lightweight hardware security primitive, physical unclonable functions (PUFs) can provide reliable identity authentication for devices of Internet of Things (IoTs) with limited resources. However, the delay-based PUF structures in authentication protocols have static responding behaviors, which make them vulnerable to modeling attacks. To address this issue, many complex PUF designs have been designed to increase the nonlinearity of their models. However, most of them can still be broken by modeling-based machine learning (ML) attacks. In this article, a dynamic responding mechanism for PUF designs to generate dynamic responses is proposed. Different from the concept of logically reconfigurable PUFs, the proposed mechanism does not rely on external inputs to provide reconfiguration signals. And different from the conventional PUF authentication protocols that use large-size linear feedback shift register (LFSR) to extend the master challenge, the proposed scheme uses internally generated dynamic signals to obfuscate the master challenge to generate multiple subchallenges. These subchallenges are then input to the underlying strong PUF to generate multibit dynamic responses. It can prevent an attacker from obtaining valid challenge-response pairs (CRPs) for the underlying PUF. A security authentication protocol is also proposed, the special authentication bit-string design can resist both conventional ML attacks and the latest covariance matrix adaptation evolution strategies (CMA-ES) variant. [ABSTRACT FROM AUTHOR]

Secure model aggregation across many users is a key component of federated learning systems. The state-of-the-art protocols for secure model aggregation, which are based on additive masking, require all users to quantize their model updates to the same level of quantization. This severely degrades their performance due to lack of adaptation to available communication resources, e.g., bandwidth, at different users. As the main contribution of our paper, we propose HeteroSAg, a scheme that allows secure model aggregation while using heterogeneous quantization. HeteroSAg enables the edge users to adjust their quantization proportional to their available communication resources, which can provide a substantially better trade-off between the accuracy of training and the communication time. Our proposed scheme is based on a grouping strategy by partitioning the network into groups, and partitioning the local model updates of users into segments. Instead of applying aggregation protocol to the entire local model update vector, it is applied on segments with specific coordination between users. We further demonstrate how HeteroSAg can enable Byzantine robustness while achieving secure aggregation simultaneously. Finally, we prove the convergence guarantees of HeteroSAg under heterogeneous quantization in the non-Byzantine scenario. [ABSTRACT FROM AUTHOR]

Many IoT devices lack the necessary interfaces (keyboards, screens) for entering passwords or changing default ones. For these devices, bootstrapping trust can be challenging. We address the problem of device pairing in the absence of any shared secrets. Pairing is a two-phase process that requires mutual authentication between the two parties and the agreement to a common key that can be used to further bootstrap essential cryptographic mechanisms. We propose a secret-free and in-band trust establishment protocol that achieves the secure pairing of commercial off-the-shelf (COTS) wireless devices with a hub. As compared to the state-of-the-art, our protocol does not require any hardware/firmware modification to the devices, or any out-of-band channels, but can be applied to any COTS device. Furthermore, our protocol is resistant to active signal manipulations attacks that include recently demonstrated signal nullification at an intended receiver. These security properties are achieved in-band with the assistance of a helper device such as a smartphone and by exploiting hard-to-forge signal propagation laws. We perform extensive theoretical analysis to verify the security of the proposed protocol. In addition, we validate our theoretical results with experiments using COTS devices and USRP radios. [ABSTRACT FROM AUTHOR]

Security is a key problem for the transmission, interchange, and storage process of multimedia systems and applications. In 2018, Li et al. proposed in-depth security analysis on an image encryption algorithm based on a first-order time-delay system (IEATD) and gave a specific chosen-plaintext attack on it. Moreover, an enhanced version called as IEACD was designed to fix the reported security defects. This article analyzes the essential structures of the two algorithms and evaluates their real security performances: 1) no efficient nonlinear operations are adopted to assure the sensibility of keystream; 2) the equivalent secret key of IEATD can be efficiently recovered from one known plain-image and the corresponding cipher-image; and 3) IEACD can still be efficiently cracked with a chosen-plaintext attack. Both rigorous theoretical analyses and detailed experimental results are provided to demonstrate effectiveness of the advanced cryptanalytic methods. [ABSTRACT FROM AUTHOR]

The concept of the smart city and the extensive use of vehicles are evolving progressively. This evolution makes vehicular ad-hoc network (VANET) a widely used network for inter-vehicular communication to get information about speed, traffic congestion, road condition, and vehicle location. This information is obtained from a public network, which is prone to various attacks. Generally speaking, data security in VANET is one of the most crucial tasks. We found many authentication protocols for VANETs; however, most of these protocols are insecure due to impersonation, replay, denial of service attacks, etc. Moreover, the existing protocols utilized heavy computation and communication costs, making them incompatible for resource-constrained VANET applications. This article presents a lightweight privacy-preserving authentication protocol for VANETs to offer a secure and efficient data transmission mechanism over a public channel. We analyze that our protocol is lightweight, safe, and scalable compared to related protocols. The communication and computation cost of our protocol is less concerning the state-of-the-art protocols. Hence, it is overt from the observed facts that our protocol is more reliable, convenient, and practical for secure data transmission in VANETs. [ABSTRACT FROM AUTHOR]

Until now, the pseudonym ID and one-time hash chain as the key technologies solve anonymous and forward secrecy properties, respectively, in lightweight authentication protocols for wireless sensor networks (WSNs) environment. However, both techniques have to face the limitation of asynchronization attack, which will cause the pseudonym ID and one-time hash chain value between participants to be loss of synchronization when the transmitted message is blocked. Most recently, a serial of lightweight anonymous authentication scheme with forward secrecy (LAASFS) have been built to resolve this problem. Unfortunately, they failed to handle this question satisfactorily. Besides, most of them are still vulnerable to smart card loss attack (SCLA). In this article, to address these issues and make more effective, we combine pseudonym ID, one-time hash chain and tag techniques to construct an LAASFS for WSNs environment. The proposed LAASFS can be adaptive resilience of asynchronization attacks. In addition, it is also able to resist a variety of known attacks like SCLA and wrong password login attack. Formal analyses are taken by BAN logic and ProVerif tool to demonstrate the security of properties of our LAASFS. Compared with several previous related schemes, the proposed LAASFS possesses obvious advantages in computation and communication costs. [ABSTRACT FROM AUTHOR]

Space information networks (SINs) can be viewed as an expansion of a conventional network with a strong demand for high-speed, reliable, and real-time wireless communication, especially in extreme circumstances. However, there are a number of challenges associated with deploying SINs. With the emergence and wide application of blockchain technology, it is expected to relieve the trust issues of communication systems in SINs. In this article, we first propose a decentralized blockchain architecture for SINs, taking advantage of the increasing computation and communication capabilities of satellites. Then, by utilizing blockchain, we present two communication protocols, Fulgor and Rayo, designed for different application scenarios in SINs: Fulgor is a secure communication protocol between users and the ground station based on our proposed efficient authentication and key agreement protocol. Rayo is a user-to-user priva-cy-preserving communication protocol to protect the user's privacy and avoid DoS attacks. Finally, experiments are conducted and performed on a widely known blockchain platform, Hyperledger Fabric, and the findings demonstrate our proposal's feasibility. [ABSTRACT FROM AUTHOR]

Advancements in quantum computing present a security threat to classical cryptography algorithms. Lattice-based key exchange protocols show strong promise due to their resistance to theoretical quantum-cryptanalysis and low implementation overhead. By contrast, their physical implementations have shown vulnerability against side-channel attacks (SCAs) even with a single power measurement. The state-of-the-art SCAs are, however, limited to simple, sequentialized executions of post-quantum key-exchange (PQKE) protocols, leaving the vulnerability of complex, parallelized architectures unknown. This article proposes 2Deep—a deep-learning (DL)-based SCA—targeting parallelized implementations of PQKE protocols, namely, Frodo and NewHope with data augmentation techniques. Specifically, we explore approaches that convert 1-D time-series power measurement data into 2-D images to formulate SCA an image recognition task. The results show our attack’s superiority over conventional techniques including horizontal differential power analysis (DPA), template attacks (TAs), and straightforward DL approaches. We demonstrate improvements up to 1.5 × to recover a 100% success rate compared to DL with 1-D input data while using fewer data. We furthermore show that machine learning improves the results up to 1.25 × compared to TAs. Furthermore, we perform cross-device attacks that obtain profiles from a single device, which has never been explored. Our 2-D approach is especially favored in this setting, improving the success rate of attacking Frodo from 20% to 99% compared to the 1-D approach. Our work thus urges countermeasures even on parallel architectures and single-trace attacks. [ABSTRACT FROM AUTHOR]

Silicon physical unclonable function (PUF) has emerged as a promising spoof-proof solution for low-cost device authentication. Due to practical constraints in preventing phishing through a public network or insecure communication channels, simple PUF-based authentication protocol with unrestricted queries and transparent responses is vulnerable to modeling and replay attacks. In this article, we present a modeling attack resistant PUF-based mutual authentication scheme to mitigate the practical limitations in applications where a resource-rich server authenticates a device with no strong restriction imposed on the type of PUF design or any additional protection on the binary channel used for the authentication. Our scheme uses an active deception protocol to prevent machine learning (ML) attacks on a device with a monolithic integration of a genuine strong PUF (SPUF), a fake PUF, a pseudorandom number generator (PRNG), a register, a binary counter, a comparator, and a simple controller. The hardware encapsulation makes the collection of challenge–response pairs (CRPs) easy for model building during enrollment but prohibitively time consuming upon device deployment through the same interface. A genuine server can perform a mutual authentication with the device using a combined fresh challenge contributed by both the server and the device. The message exchanged in clear cannot be manipulated by the adversary to derive unused authentic CRPs. The adversary will have to either wait for an impractically long time to collect enough real CRPs by directly querying the device or the ML model derived from the collected CRPs will be poisoned. The false PUF multiplexing is fortified against the prediction of waiting time by doubling the time penalty for every unsuccessful guess. Our implementation results on field-programmable gate array (FPGA) device and security analysis have corroborated the low hardware overheads and attack resistance of the proposed deception protocol. [ABSTRACT FROM AUTHOR]

Technological development expands the computation process of smart devices that adopt the telecare medical information system (TMIS) to fulfill the demands of the healthcare organization. It provides better medical identification to claim the features namely trustworthy, efficient, and resourceful. Moreover, the telecare services automate the remote healthcare monitoring process to ease professional workloads. Importantly, it is conceived to be more timesaving, economical, and easy healthcare access. Cloud-Based Medical Healthcare (CBMH) system is a standard platform that gives its support to the patients for emergency treatment from the medical experts over Internet communication. Since the medical records are very sensitive, security protection is much necessitated. In addition, patient anonymity should be well preserved. In 2016, Chiou et al. proposed a mutual authentication protocol for the Telecare Medical Information System (TMIS) using Cloud Environment (CE). They claim that their protocol satisfies patient anonymity. However, this paper proves that the Chiou et al. scheme is not only completely insecure against the patient anonymity, health-report revelation, health-report forgery, report confidentiality, and non-repudiation but also fails to validate the service access against verifiability, undeniability and unforgeability. In order to provide better mutual authenticity, this paper suggests the framework of smart service authentication to cross-examine the common secret session key among the communication entities. In order to examine the security properties, formal and informal verification was carried out. Lastly, to prove the security and performance efficiency of a system, the proposed SSA framework was implemented using FPGA and Moteiv TMote Sky-Mote. A proposed smart service authentication (SSA) framework is presented to ensure better data security between the patients and the physicians. The formal and informal security analysis proves the significance of the SSA framework model to withstand the security attacks such as health-report forgery, health-report revelation, server-spoofing etc. As a result, it is claimed that it can be well suited for TMIS. [ABSTRACT FROM AUTHOR]

Unmanned Aerial Vehicles (UAVs) are becoming very popular nowadays due to the emergence of application areas such as the Internet of Drones (IoD). They are finding wide applicability in areas ranging from package delivery systems to automated military applications. Nevertheless, communication security between a UAV and its ground station (GS) is critical for completing its task without leaking sensitive information either to the adversaries or to unauthenticated users. UAVs are especially vulnerable to physical capture and node tampering attacks. Further, since UAV devices are generally equipped with small batteries and limited memory storage, lightweight security techniques are best suited for them. Addressing these issues, a lightweight mutual authentication scheme based on Physical Unclonable Functions (PUFs) for UAV-GS authentication is presented in this paper. The UAV-GS authentication scheme is extended further to support UAV-UAV authentication. We present a formal security analysis as well as old-fashioned cryptanalysis and show that our protocol provides various security features such as mutual authentication, user anonymity, etc, and is resilient against many security attacks such as masquerade, replay, node tampering, and cloning attacks, etc. We also compare the performance of our protocol with state-of-the-art authentication protocols for UAVs, based on computation, communication, and memory storage cost. [ABSTRACT FROM AUTHOR]

The byzantine agreement protocol has a disadvantage that there are many limitations on node scalability, because the performance degradation may occur due to a large amount of traffic. Hence, this classical byzantine agreement algorithm seems to be infeasible to achieve scale-out performance with the same level of security as a Bitcoin. In order to improve the performance degradation due to a large amount of traffic, we propose the hierarchical consensus mechanism based on service-zone sharding rather than how all nodes participate in the consensus process. In the proposed consensus mechanism (SZHBFT), a disjoint set of transactions is locally processed by a secure consensus subgroup or globally processed between consensus subgroups. Thus, the transactions that occur related to multiple Service-Zone Consensus Groups are updated and maintained in the Inter-Service Zone Public Ledger, whereas service transactions occurring locally are processed in parallel by each Service-Zone Consensus Group and then distributed into a local Service-Zone Private Ledger. The scheme of the proposed SZHBFT mechanism provides the hierarchical agreement solution along with distributed multiledger structure for the scalable byzantine resilient agreement by forming secure consensus subgroups in order to minimize the overhead of overall communication messages. [ABSTRACT FROM AUTHOR]

There has been a a significant increase in the popularity of using Unmanned Aerial Vehicles (UAVs), popularly known as drones, in several applications. In many application scenarios, UAVs are deployed in missions where sensitive data is collected, such as monitoring critical infrastructure, industrial facilities, crops, and public safety. Due to the sensitive and/or safety critical nature of the data collected in these applications, it is imperative to consider the security, and privacy aspects of the UAVs used in these scenarios. In this article, we propose an efficient privacy aware authenticated key agreement scheme for edge-assisted UAVs (Internet of Drones). Unlike the existing security solutions for UAVs, the proposed scheme does not need to store any secret keys in the devices but still can provide the desired security features. To the best of our knowledge, this is the first work where physical security of the UAV has been taken into account. The proposed system allows third-party communication, and mobile edge computing service providers to authenticate the UAVs without any loss of provacy, and outperforms existing methods in terms of computational complexity. [ABSTRACT FROM AUTHOR]

The FlexRay protocol provides deterministic and fault-tolerant communication for automotive applications with stringent requirements regarding reliability and real-time performance. But the lack of intrinsic security mechanisms makes FlexRay vulnerable to spoofing and DoS attacks while existing features are not sufficient to assure reliable communication in the presence of adversaries. Since adding cryptography mandates for secret shared keys, providing secure key establishment techniques is critical in assuring the intended security objectives. In this paper we propose a backward compatible key agreement scheme for FlexRay communication based on intrinsic characteristics of the FlexRay physical layer. In particular, we determine that the symbol window is suitable for implementing a covert channel based on physical properties of the bus which allows us to bootstrap a secure session key between two nodes or to re-enforce existing shared keys. We evaluate and discuss the performance of software-based implementations of the proposed mechanism on two different automotive embedded platforms relying only on the application level. [ABSTRACT FROM AUTHOR]

Device-to-device communication is widely used for mobile devices and Internet of Things. Authentication and key agreement are critical to build a secure channel between two devices. However, existing approaches often rely on a pre-built fingerprint database and suffer from low key generation rate. We present GeneWave, a fast device authentication and key agreement protocol for commodity mobile devices. GeneWave first achieves bidirectional initial authentication based on the physical response interval between two devices. To keep the accuracy of interval estimation, we eliminate time uncertainty on commodity devices through fast signal detection and redundancy time cancellation. Then, we derive the initial acoustic channel response for device authentication. We design a novel coding scheme for efficient key agreement while ensuring security. Therefore, two devices can authenticate each other and securely agree on a symmetric key. GeneWave requires neither special hardware nor pre-built fingerprint database, and thus it is easy-to-use on commercial mobile devices. We implement GeneWave on mobile devices (i.e., Nexus 5X and Nexus 6P) and evaluate its performance through extensive experiments. Experimental results show that GeneWave efficiently accomplish secure key agreement on commodity smartphones with a key generation rate 10 $\times$ faster than the state-of-the-art approach. [ABSTRACT FROM AUTHOR]

For the multiterminal secret key agreement problem under a private source model, it is known that the maximum key rate, i.e., the secrecy capacity, can be achieved through communication for omniscience, but the omniscience strategy can be strictly suboptimal in terms of minimizing the public discussion rate. While a single-letter characterization is not known for the minimum discussion rate needed for achieving the secrecy capacity, we derive single-letter lower bounds that yield some simple conditions for omniscience to be discussion-rate optimal. These conditions turn out to be enough to deduce the optimality of omniscience for a large class of sources, including the hypergraphical sources. We also extend our results to more general class of multiterminal sources with helpers and silent users. [ABSTRACT FROM AUTHOR]

Two parties observing correlated random variables seek to run an interactive communication protocol. How many bits must they exchange to simulate the protocol, namely to produce a view with a joint distribution within a fixed statistical distance of the joint distribution of the input and the transcript of the original protocol? We present an information spectrum approach for this problem whereby the information complexity of the protocol is replaced by its information complexity density. Our single-shot bounds relate the communication complexity of simulating a protocol to tail bounds for information complexity density. As a consequence, we obtain a strong converse and characterize the second-order asymptotic term in communication complexity for independent and identically distributed observation sequences. Furthermore, we obtain a general formula for the rate of communication complexity, which applies to any sequence of observations and protocols. Connections with results from theoretical computer science and implications for the function computation problem are discussed. [ABSTRACT FROM PUBLISHER]

Telecare medicine information systems (TMIS) provide flexible and convenient e-health care. However, the medical records transmitted in TMIS are exposed to unsecured public networks, so TMIS are more vulnerable to various types of security threats and attacks. To provide privacy protection for TMIS, a secure and efficient authenticated key agreement scheme is urgently needed to protect the sensitive medical data. Recently, Mishra et al. proposed a biometrics-based authenticated key agreement scheme for TMIS by using hash function and nonce, they claimed that their scheme could eliminate the security weaknesses of Yan et al.'s scheme and provide dynamic identity protection and user anonymity. In this paper, however, we demonstrate that Mishra et al.'s scheme suffers from replay attacks, man-in-the-middle attacks and fails to provide perfect forward secrecy. To overcome the weaknesses of Mishra et al.'s scheme, we then propose a three-factor authenticated key agreement scheme to enable the patient to enjoy the remote healthcare services via TMIS with privacy protection. The chaotic map-based cryptography is employed in the proposed scheme to achieve a delicate balance of security and performance. Security analysis demonstrates that the proposed scheme resists various attacks and provides several attractive security properties. Performance evaluation shows that the proposed scheme increases efficiency in comparison with other related schemes. [ABSTRACT FROM AUTHOR]

Public key infrastructure (PKI) is the most widely used security mechanism for securing communications over the network. However, there are known performance issues, making it unsuitable for use in vehicular networks. In this paper, we propose a secure and authenticated key management protocol (SA-KMP) to overcome the shortcomings of the PKI. The SA-KMP scheme distributes repository containing the bindings of the entity's identity and its corresponding public key to each vehicle and road side unit. By doing so, certificate exchanges and certificate revocation lists are eliminated. Furthermore, the SA-KMP scheme uses symmetric keys derived based on a 3-D-matrix-based key agreement scheme to reduce the high computational costs of using asymmetric cryptography. We demonstrate the efficiency of the SA-KMP through performance evaluations in terms of transmission and storage overhead, network latency, and key generation time. Analytical results show that the SA-KMP is more scalable and outperforms the certificate-based PKI. Simulation results indicate that the key generation time of the SA-KMP scheme is less than that of the existing Elliptic Curve Diffie–Hellman and Diffie–Hellman protocols. In addition, we use Proverif to prove that the SA-KMP scheme is secure against an active attacker under the Dolev and Yao model and further show that the SA-KMP scheme is secure against denial of service, collusion attacks, and a wide range of other malicious attacks. [ABSTRACT FROM PUBLISHER]

VANET (vehicular ad hoc network) is used to create communication networks for vehicles or other roadside devices so that they can quickly share and receive messages. However, VANET belongs to a family of wireless networks, which means that its functions are unsafe. To provide safe communication channels, key-agreements technology can be introduced to VANET communication. Traditional key-agreement schemes, however, are inefficient and consume too many resources, especially when handling large or combined groups of users. To improve efficiency, the Chinese remainder theorem is used to build a batch key-agreement protocol. The improved key for VANET environments is a safer and quicker way to establish communication channels. [ABSTRACT FROM PUBLISHER]

We consider secret-key agreement with public discussion over multiple-input multiple-output (MIMO) Rayleigh fast-fading channels under correlated environment. We assume that transmit, legitimate receiver, and eavesdropper antennas are correlated. The legitimate receiver and the eavesdropper are assumed to have perfect channel knowledge while the transmitter has only knowledge of the correlation matrices. First, we derive the expression of the secret-key capacity under the considered setup. We prove that the optimal transmit strategy achieving the secret-key capacity consists in transmitting independent Gaussian signals along the eingenvectors of the transmit correlation matrix. The powers allocated to each channel mode are determined as the solution to a numerical optimization problem. A necessary and sufficient condition for beamforming (i.e., transmitting along the strongest channel mode) to be capacity-achieving is derived. Moreover, we analyze the impact of correlation matrices on the system performance. Finally, we study the system’s performance in the two extreme power regimes. In the high-power regime, we provide closed-form expressions of the gain/loss due to correlation. In the low signal-to-noise ratio (SNR) regime, we investigate the energy efficiency of the system by determining the minimum energy required for sharing a secret-key bit and the wideband slope while highlighting the impact of correlation matrices. [ABSTRACT FROM AUTHOR]

Theorem 5 of A. Gohari, V. Anantharam, IEEE Transactions on Information Theory, vol. 56, no. 8, pp. 3973-3996, 2010, states an upper bound on the secrecy capacity for the source model problem. It has a three page proof given in Appendix B of the paper. Unfortunately, we show that this bound does not provide any improvement over the simpler bound given in Corollary 1 of the paper. We also provide an example of a family of two agent source model problems where the one-way secrecy rate in each direction is zero, but the secrecy rate is nonzero and can be determined exactly as a conditional mutual information. [ABSTRACT FROM AUTHOR]

A secret key agreement framework involving three users is considered in which each of the users 1 and 2 intends to share a secret key with user 3 and users 1 and 2 are eavesdroppers with respect to each other. There is a generalized discrete memoryless multiple access channel (GDMMAC) from users 1 and 2 to user 3 where the three users receive outputs from the channel. Furthermore, there is a feedback channel from user 3 to users 1 and 2 through which user 3 sends information extracted from the received output from the GDMMAC to increase the key rates. We consider both noiseless and noisy feedback. In the case of noiseless feedback, a public channel of unlimited capacity from user 3 to users 1 and 2 is used only once. In the case of noisy feedback, a noisy broadcast channel (BC) from user 3 to users 1 and 2 can be repeatedly used, like GDMMAC. In both setups, inner bounds of the secret key capacity region are derived. The secret key capacity region is derived in some special cases where the channel inputs and outputs form Markov chains in certain orders. For illustration, the corresponding results are also derived and discussed for Gaussian channels. The cases with noiseless feedback, noisy feedback, and no feedback at all are compared with each other. [ABSTRACT FROM AUTHOR]

Consider two parties holding samples from correlated distributions W and W^\prime, respectively, where these samples are within distance t of each other in some metric space. The parties wish to agree on a close-to-uniformly distributed secret key R by sending a single message over an insecure channel controlled by an all-powerful adversary who may read and modify anything sent over the channel. We consider both the keyless case, where the parties share no additional secret information, and the keyed case, where the parties share a long-term secret \ssr SK\ssr Ext that they can use to generate a sequence of session keys \Rj\ using multiple pairs \(Wj, W^{\primej)\}. The former has applications to, e.g., biometric authentication, while the latter arises in, e.g., the bounded-storage model with errors. We show solutions that improve upon previous work in several respects. numeration="arabic" continuation="restarts" posttext=")" The best prior solution for the keyless case with no errors (i.e., t=0) requires the min-entropy of W to exceed 2n/3, where n is the bit length of W. Our solution applies whenever the min-entropy of W exceeds the minimal threshold n/2, and yields a longer key. [ABSTRACT FROM AUTHOR]

The aim of this paper is to prove coding theorems for the wiretap channel and the secret key agreement based on the the notion of a hash property for an ensemble of functions. These theorems imply that codes using sparse matrices can achieve the optimal rate. Furthermore, fixed-rate universal coding theorems for a wiretap channel and a secret key agreement are also proved. [ABSTRACT FROM AUTHOR]