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With the proliferation of new mobile devices, mobile cloud computing technology has emerged to provide rich computing and storage functions for mobile users. The explosive growth of mobile data has led to an increased demand for solutions that conserve storage resources. Data deduplication is a promising technique that eliminates data redundancy for storage. For mobile cloud storage services, enabling the deduplication of encrypted data is of vital importance to reduce costs and preserve data confidentiality. However, recently proposed solutions for encrypted deduplication lack the desired level of security and efficiency. In this paper, we propose a novel scheme for serverless efficient encrypted deduplication (SEED) in mobile cloud computing environments. Without the aid of additional servers, SEED ensures confidentiality, data integrity, and collusion resistance for outsourced data. The absence of dedicated servers increases the effectiveness of SEED for mobile cloud storage services, in which user mobility is essential. In addition, noninteractive file encryption with the support of lazy encryption greatly reduces latency in the file-upload process. The proposed indexing structure (D-tree) supports the deduplication algorithm and thus makes SEED much more efficient and scalable. Security and performance analyses prove the efficiency and effectiveness of SEED for mobile cloud storage services.

A secure deduplication technique removes duplicate data and stores only single copy to efficiently utilize the storage while guaranteeing the privacy of the data. Thus, it is a necessary technology for resource-limited for devices to save storages. However, most of the existing deduplication schemes based on convergent encryption suffer from 1) a convergent encryption key management problem and 2) a dynamic ownership management problem. In key management, convergent encryption generates a number of encryption keys whose size increases linearly with the number of distinct data. In terms of dynamic ownership management, although the ownership of data in a fog device or cloud storage frequently changes in real-world applications, supporting ownership changes are difficult because the convergent encryption keys are only bound to the data. In order to solve these problems, we present a secure deduplication scheme that features reliable and scalable key management based on pairing-based cryptography and supports dynamic ownership management. The proposed scheme avoids additional costs associated with distributing key components on secure channels and ownership keys on the user side yet guarantees secure key and ownership management.

In cloud-assisted data outsourcing systems, the privacy of sensitive data is a major concern. Thus, data are uploaded in encrypted form in many cloud applications while providing some basic yet critical functionalities, such as the ability to search. Similarity search over encrypted data provides decryptionless similarity testing between data and search queries which are encrypted by the data owner and users, respectively. However, previous similarity search schemes supporting multi-user settings incur unreasonable communication costs between the users and data owners during the search. In this paper, we propose efficient multi-user similarity search schemes for cloud storage. Specifically, the proposed schemes enable flexible similarity searches over encrypted data even when the given data have different format, encoding, or editing. The proposed similarity search schemes can guarantee asymptotically optimal performance for multi-user settings. We rigorously prove the proposed schemes are adaptively semantic secure. We also conduct an experimental analysis to demonstrate the applicability of the proposed scheme in practical cloud systems.

The explosion in the volume of data generated by end-point devices, arising from IoT proliferation, has lead to the adoption of data outsourcing to dedicated data centers. However, centralized data centers such as cloud storage cannot afford to manage large stores of data in a timely manner. To allow low latency access to large amounts of data, a new computing paradigm, called fog computing, has been introduced. In a fog computing environment, privacy issues surrounding outsourced data become more critical due to its complicated innards of the system. In addition, efficient resource management is another important criterion considering the application of pay-per-use in commercial fog storage. As an extension of cloud storage, most fog storage service providers will choose to adopt data deduplication techniques to minimize resource dissipation. At the same time, data owners may update or remove outsourced data stored in the remote storage to reduce expenses. In this paper, we propose the first privacy-preserving deduplication protocol capable of efficient ownership management in fog computing. It achieves fine-grained access control by introducing user-level key management and update mechanisms. Data-invariant user-level private keys enable data owners to maintain a constant number of keys regardless of the number of outsourced data files. The update of user-level public keys for valid data owners at the remote storage dramatically reduces communication overhead. Security and performance analyses demonstrate the efficiency of the proposed scheme in terms of communication and key management in fog storage.

Data deduplication has attracted many cloud service providers (CSPs) as a way to reduce storage costs. Even though the general deduplication approach has been increasingly accepted, it comes with many security and privacy problems due to the outsourced data delivery models of cloud storage. To deal with specific security and privacy issues, secure deduplication techniques have been proposed for cloud data, leading to a diverse range of solutions and trade-offs. Hence, in this article, we discuss ongoing research on secure deduplication for cloud data in consideration of the attack scenarios exploited most widely in cloud storage. On the basis of classification of deduplication system, we explore security risks and attack scenarios from both inside and outside adversaries. We then describe state-of-the-art secure deduplication techniques for each approach that deal with different security issues under specific or combined threat models, which include both cryptographic and protocol solutions. We discuss and compare each scheme in terms of security and efficiency specific to different security goals. Finally, we identify and discuss unresolved issues and further research challenges for secure deduplication in cloud storage.

Searchable encryption (SE) supports privacy-preserving searches over encrypted data. Recent studies on SE have focused on improving efficiency of the schemes. However, it was shown that most of the previous SE schemes could reveal the client's queries even if they are encrypted, thereby leading to privacy violation. In order to solve the problem, several forward private SE schemes have been proposed in a single client environment. However, the previous forward private SE schemes have never been analyzed in multi-client settings. In this paper, we briefly review the previous forward private SE schemes. Then, we conduct a comparative analysis of them in terms of performance and forward privacy. Our analysis demonstrates the previous forward secure SE schemes highly depend on the file-counter. Lastly, we show that they are not scalable in multi-client settings due to the performance and security issue from the file-counter.

With the rapid growth in the development of smart devices equipped with biometric sensors, client identification system using biometric traits are widely adopted across various applications. Among many biometric traits, fingerprint-based identification systems have been extensively studied and deployed. However, to adopt biometric identification systems in practical applications, two main obstacles in terms of efficiency and client privacy must be resolved simultaneously. That is, identification should be performed at an acceptable time, and only a client should have access to his/her biometric traits, which are not revocable if leaked. Until now, multiple studies have demonstrated successful protection of client biometric data; however, such systems lack efficiency that leads to excessive time utilization for identification. The most recently researched scheme shows efficiency improvements but reveals client biometric traits to other entities such as biometric database server. This violates client privacy. In this paper, we propose an efficient and privacy-preserving fingerprint identification scheme by using cloud systems. The proposed scheme extensively exploits the computation power of a cloud so that most of the laborious computations are performed by the cloud service provider. According to our experimental results on an Amazon EC2 cloud, the proposed scheme is faster than the existing schemes and guarantees client privacy by exploiting symmetric homomorphic encryption. Our security analysis shows that during identification, the client fingerprint data is not disclosed to the cloud service provider or fingerprint database server.

A major challenge achieving scalable access control for a large number of subscribers in a public broadcast is to distribute key update messages reliably to all stateless receivers. However, in a public broadcast, the rekeying messages can be dropped or compromised during transmission over an insecure broadcast channel, or transmitted to receivers while they were off-line. In this study, we propose a novel group key management scheme. It features a mechanism to allow legitimate receivers to recover the current group key, even if they lose key update messages for long-term sessions. The scheme uses short hint messages and member computation. Performance analysis shows that the proposed scheme has the advantages of scalability and efficient rekeying compared to previous reliable group key distribution schemes. The proposed key management scheme targets a conditional access system in a media broadcast in which there is no feedback channel from receivers to the broadcasting station.

With the dramatic increase of the number of mobile devices such as smartphones and tablet PCs, mobile traffic has increased enormously. Especially, the multimedia data accounts for bulk of the traffic transmitted in mobile networks. To accommodate this growth, device-to-device connection (D2D), which provides infra-connection off-loading, is receiving significant attention. However, we have observed that the majority of the current D2D protocols including Bluetooth and Wi-Fi Direct are vulnerable to man-in-the-middle (MITM) and replay attacks in mobile multi-hop networks. To resolve this problem, in this paper, we propose a novel D2D authentication protocol with a secure initial key establishment using ciphertext-policy attribute-based encryption (CP-ABE). By leveraging CP-ABE, the proposed scheme allows the communicating parties to mutually authenticate and derive the link key in an expressive and secure manner in a multi-hop network environment. We also propose several variations of the proposed scheme for different scenarios in a multi-hop networks without network infrastructure. We prove that the proposed scheme is secure against MITM and replay attack in D2D mobile multi-hop networks. Experimental results indicate that the proposed scheme incurs reasonable computation cost in the real world.

Data prefetching is a hardware-based optimization mechanism used in most of the modern microprocessors. It fetches data to the cache before it is needed. In this paper, we present a novel microarchitectural attack that exploits the prefetching mechanism. Our attack targets Instruction pointer (IP)-based stride prefetching in Intel processors. Stride prefetcher detects memory access patterns with a regular stride, which are likely to be found in lookup table-based cryptographic implementations. By monitoring the prefetching activities near the lookup table, attackers can extract sensitive information such as secret keys from victim applications. This kind of leakage from prefetching has never been considered in the design of constant time algorithm to prevent side-channel attacks. We show the potential of the proposed attack by applying it against the Elliptic Curve Diffie-Hellman (ECDH) algorithm built upon the latest version of OpenSSL library. To the best of our knowledge, this is the first microarchitectural side-channel attack exploiting the hardware prefetching of modern microprocessors.

Honey encryption (HE) is a novel password-based encryption scheme that is secure against brute-force attacks even if users’ passwords have min-entropy. However, in HE, decryption with an incorrect key produces fake messages that appear valid. Hence, password typographical errors may confuse even legitimate users. This has been one of the most challenging problems in HE. To tackle this challenge, we propose three types of protocols that enable legitimate users to detect password typographical errors in HE. We conducted a theoretical analysis and performed an IRB-approved user study with 150 participants to compare the performance of each scheme. We also analyzed the security of the proposed schemes against online and offline brute-force attacks. The results from the user study and theoretical analysis show that the proposed schemes can effectively solve the typographical error problem of HE, which can detect typographical errors with 99% accuracy.

For building a secure cloud storage service on top of a public cloud infrastructure, attribute-based encryption (ABE) has been a preferred solution due to its flexible access control. ABE, however, incurs heavy computation cost on users during decryption. Thus, previous studies solved this problem by enabling cloud servers to perform a part of decryption operations on behalf of the users. In order to empower users to verify the correctness of the delegated decryption by the cloud, they employed a cryptographic commitment or message authentication code (MAC) to enable users to check the correctness of partial decryption of the cloud. However, the previous schemes fail to ensure the correctness of computation in the presence of malicious cloud servers. In this paper, we propose a novel and generic commitment scheme for ABE, which is secure against tampering attacks by malicious cloud servers. According to the performance analysis, the proposed scheme is only 0.5 ms slower on average than the previous commitment-based schemes and two to three times faster than the MAC-based scheme.

To achieve high storage saving, data deduplication techniques are widely used in many practical cloud storage services, which removes redundant data and keeps only a single copy of them. However, secure data deduplication over encrypted data is challenging since encryption may result in different ciphertexts even when the original messages are the same. Thus, message-locked encryption (MLE) is proposed to solve this issue and demonstrates that it is secure under the unpredictable message set. Since block-level deduplication can achieve more fine-grained storage saving, several block-level deduplication schemes that support updatability are also vividly proposed. However, the previous updatable block-level MLE schemes are vulnerable against brute-force attack when the message set is predictable. Since the size of a block is typically much less than an arbitrary size of a file, the predictability problem is a very important pragmatic concern which should be addressed in the block-level deduplication literature. In this paper, thus, we propose a novel secure block-level deduplication scheme that guarantees efficient data update and brute-force attack resilience even when messages are predictable with the rigorous security proof. Also, our performance evaluation shows that additional time and bandwidth usage can be minimized as the size of a block increases.

Arazi was the first author to propose the integration of a key exchange protocol with a digital signature algorithm. Other authors have subsequently proposed methods to increase the level of security and achieve the necessary properties of authenticated key exchange protocols. However, these proposals exhibit several weaknesses and the majority of these protocols are based only on a single hard problem. In this paper, we propose a new secured key exchange protocol which is based on two hard problems. We then extend this to a signcryption protocol and a deniable signcryption protocol. These protocols represent the first steps in a new direction, but they are designed based on two hard problems. The security proofs for the new protocols confirm their novelty and security.

Explosion of multimedia content brings forth the needs of efficient resource utilization using the state of the arts cloud computing technologies such as data deduplication. In the cloud computing environments, achieving both data privacy and integrity is the challenging issue for data outsourcing service. Proof of Storage with Deduplication (POSD) is a promising solution that addresses the issue for the cloud storage systems with deduplication enabled. However, the validity of the current POSD scheme stands on the strong assumption that all clients are honest in terms of generating their keys. We present insecurity of this approach under new attack model that malicious clients exploit dishonestly manipulated keys. We also propose an improved POSD scheme to mitigate our attack.

Recently, there has been an explosive increase in the volume of multimedia data that is available as a result of the development of multimedia technologies. More and more data is becoming available on a variety of web sites, and it has become increasingly cost prohibitive to have a single data server store and process multimedia files locally. Therefore, many service providers have been likely to outsource data to cloud storage to reduce costs. Such behavior raises one serious concern: how can data users be authenticated in a secure and efficient way? The most widely used password-based authentication methods suffer from numerous disadvantages in terms of security. Multi-factor authentication protocols based on a variety of communication channels, such as SMS, biometric, or hardware tokens, may improve security but inevitably reduce usability. To this end, we present a data block-based authentication scheme that is secure and guarantees usability in such a manner where users do nothing more than enter a password. In addition, the proposed scheme can be effectively used to revoke user rights. To the best of our knowledge, our scheme is the first data block-based authentication scheme for outsourced data that is proven to be secure without degradation in usability. An experiment was conducted using the Amazon EC2 cloud service, and the results show that the proposed scheme guarantees a nearly constant time for user authentication.

In recent years, the volume of educational contents has been explosively increased thanks to the rapid development of multimedia technologies. Furthermore, the development of smart devices has made various educational institutes use them as effective learning tools. Since more and more educational contents become available not only at school zone but at a variety of online learning systems, it becomes increasingly unaffordable for a single educational contents provider to store and process them locally. Therefore, many educational contents providers are likely to outsource the contents to cloud storage for cost saving. These phenomena raise one serious concern: how to authenticate educational contents users in a secure and efficient way? The most widely used password-based authentication suffers from numerous drawbacks in terms of security. Multi-factor authentication protocols based on diverse communication channels such as SMS, biometric, hardware token could enhance security, however they inevitably bring poor usability. To this end, we present a data block-based authentication scheme, which provides provable security and guarantees usability invariant such that users do nothing but entering a password. In addition, the proposed scheme supports efficient user revocation. To the best of our knowledge, our scheme is the first data block-based authentication scheme for outsourced educational contents that is provably secure without usability degradation. The experiment on Amazon EC2 cloud shows that the proposed scheme guarantees nearly constant time for user authentication.

Increment of multimedia data motivates users to utilize cloud storage (CS) to exploit its massive size. For this extensible storage system, there are two desirable requirements: (1) the users should be able to ensure that their outsourced data is securely protected and (2) the cloud service provider should be able to eliminate redundant copies of data for improvement of storage utilization. Conventional encryption scheme does not satisfy the deduplication on ciphertext as it destroys message equality. Recent study, DupLESS, has enhanced Convergent Encryption (CE) and provided strong privacy. However, CE-based scheme allows the users to possibly decrypt cloud data even if the user loses his ownership to the data. In order to solve this problem, we propose a secure deduplication scheme with user revocation. Our scheme leverages oblivious pseudo-random function to generate encryption key. The CS enforces data access policy using privilege-based encryption to provide user revocation. The security analysis proves that the proposed scheme is secure against unauthorized decryption by revoked users or the cloud server, and brute-force attack on predictable set of data.

A wireless electrocardiogram case study suggests that current CDMA2000 cellular technology has considerable potential in medical telemetry. Modifications to the network protocol stack ensure the highest data integrity and lowest service delay.

This paper proposes a novel hybrid model that integrates the synergy of two superior classifiers for functional magnetic resonance imaging (fMRI) recognition, namely, convolutional neural networks (CNNs) and support vector machines (SVMs), both of which have proven results in the field of image recognition. In the proposed model, the CNN functions as a trainable feature extractor and the SVM functions as a recognizer. This hybrid model extracts features from raw images and generates predictions for fMRI recognition. We conducted experiments on Haxby's 2001 fMRI dataset. Comparisons with Haxby's study using the same database indicated that the proposed fusion achieved superior recognition accuracy of 99.5% compared to the Haxby's approach. Further, when the CNN was used as a feature extractor, the SVM classifier was demonstrated to be the best combining counterpart, providing the best synergy effect in terms of accuracy. This is compared with other classifiers based on learning algorithms such as decision tree, neural network, K-nearest neighbor, random forest, and AdaBoost.

TrapFetch is trained by monitoring the read requests issued by an application. It detects bursts of disk reads, determines the appropriate addresses at which breakpoints should be inserted in the application and library codes prior to the bursts of reads, and then logs this information with the data requested during the interval between each consecutive pair of breakpoints. When the application and library codes are loaded from the disk into memory, TrapFetch inserts breakpoints at the designated addresses based on the logs. During subsequent runs, TrapFetch is invoked at each breakpoint when it prefetches the corresponding data into the page cache. This approach is effective during both launch and run-time. TrapFetch operates at the user level, thus avoiding interference with other applications. In experiments on five popular applications (FlightGear, SpeedDreams 2, Pillars of Eternity, Eclipse, and VegaStrike), TrapFetch reduced the time for launch by up to 39.7% and time for run-time data-loading by up to 63.7%.

Long-term electrocardiogram (ECG) monitoring, as a representative application of cyber-physical systems, facilitates the early detection of arrhythmia. A considerable number of previous studies has explored monitoring techniques and the automated analysis of sensing data. However, ensuring patient privacy or confidentiality has not been a primary concern in ECG monitoring. First, we propose an intelligent heart monitoring system, which involves a patient-worn ECG sensor (e.g., a smartphone) and a remote monitoring station, as well as a decision support server that interconnects these components. The decision support server analyzes the heart activity, using the Pan–Tompkins algorithm to detect heartbeats and a decision tree to classify them. Our system protects sensing data and user privacy, which is an essential attribute of dependability, by adopting signal scrambling and anonymous identity schemes. We also employ a public key cryptosystem to enable secure communication between the entities. Simulations using data from the MIT-BIH arrhythmia database demonstrate that our system achieves a 95.74% success rate in heartbeat detection and almost a 96.63% accuracy in heartbeat classification, while successfully preserving privacy and securing communications among the involved entities.

Secure deduplication using convergent encryption eliminates duplicate data and stores only one copy to save storage costs while preserving the security of the outsourced data. However, convergent encryption produces a number of encryption keys, of which size is linear to the number of different data. Although a deduplication scheme has been proposed for efficient convergent key management recently, it has drawbacks in terms of scalability and key management security. In order to solve these problems, we propose a novel secure deduplication scheme with scalable and reliable key management based on paring-based cryptography. The proposed scheme does not require additional secure channels to distribute key components while still guaranteeing secure key management as opposed to the previous schemes.

This paper proposes a conceptually simple but practical management of outsourced data for provably secure duplicate elimination with efficient storage utilization. We focus on cutting off dependency of encryption key on underlying plain data, making data owners relieved from information leakage as long as their keys are kept secret. Rather than forcing data owners for the same content to share the same key, we restrict storage space in which duplicate identification and elimination occur in order to increase (de)duplication ratio. This allows data owners to choose their own keys with no restriction, and eventually the security of the proposed approach would not be affected by other data owners as well as inside and/or outside adversaries. Our approach can be adaptively applied to existing remote storage systems according to storage capacity and security requirements.

Honey encryption (HE) is a novel password-based encryption scheme which is secure against brute-force attack even if users' passwords have min-entropy. However, because decryption under a wrong key produces fake but valid-looking messages to everyone, typos in password may confuse even legitimate users in HE. This has been one of the most challenging problems in HE. In this paper, we propose two types of protocols that enable legitimate users to detect the typos in a password. We compare and analyze the performance and security of each scheme. The analysis results show that the proposed schemes can effectively solve the typos problem in HE while providing message recovery security.

TLS protocol provides a secure communication environment by guaranteeing the confidentiality and the integrity of transmitted data between two parties. However, there have been lots of vulnerabilities in TLS protocol and attacks exploiting them in aspects of protocol, implementation, and cryptographic tools. In spite of the lessons learned from the past experiences, various attacks on the network systems are being reported continuously due to the lack of care with regard to the proper TLS deployment and management. In this paper, we investigate TLS vulnerabilities in Korea’s top 100 websites selected from Alexa global top 500 sites and 291 Korea’s public enterprise websites. We compare the analysis results with those of Alexa global top 100 websites. Then, we discuss the lessons learned from this study. In order to analyze TLS vulnerabilities efficiently, we developed a TLS vulnerability scanner, called Network Vulnerabilities Scanner (NVS). We also analyze e-mail security of Korea’s top 3 e-mail service providers, which are supposed to be secured by TLS. Interestingly, we found that the e-mail service of them is not so secured by TLS as opposed to the analysis of Google’s transparency report.

The number of subscribers in 4th generation mobile system has been increased rapidly. Along with that, preserving subscribers' privacy has become a hot issue. To prevent users' location from being revealed publicly is important more than ever. In this paper, we first show that the privacy-related problem exists in user authentication procedure in 4th generation mobile system, especially LTE. Then, we suggest an attack model which allows an adversary to trace a user, i.e. he has an ability to determine whether the user is in his observation area. Such collecting subscribers' location by an unauthorized third party may yield severe privacy problem. To keep users' privacy intact, we propose a modified authentication protocol in LTE. Our scheme has low computational overhead and strong secrecy so that both the security and efficiency are achieved. Finally, we prove that our scheme is secure by using the automatic verification tool ProVerif.

A client stores data in the cloud and uses remote data checking (RDC) schemes to check the integrity of the data. The client can detect the corruption of the data using RDC schemes. Recently, robust RDC schemes have integrated forward error-correcting codes (FECs) to ensure the integrity of data while enabling dynamic update operations. Thus, minor data corruption can be recovered by FECs, whereas major data corruption can be detected by spot-checking techniques. However, this requires high communication overhead for dynamic update, because a small update may require the client to download an entire file. The Variable Length Constraint Group (VLCG) scheme overcomes this disadvantage by downloading the RS-encoded parity data for update instead of the entire file. Despite this, it needs to download all the parity data for any minor update. In this paper, we propose an improved RDC scheme in which the communication overhead can be reduced by downloading only a part of the parity data for update while simultaneously ensuring the integrity of the data. Efficiency and security analysis show that the proposed scheme enhances efficiency without any security degradation.

Data deduplication is a technique that removes redundancy of data on the storage. For cloud storage services, enabling deduplication over encrypted data is of vital importance to achieve both cost savings and keeping data confidentiality simultaneously. Recently proposed solutions are not sufficient because of lacking desired level of security and efficiency. In this paper, we propose SEED, a novel scheme for serverless and efficient encrypted deduplication. Without aid of any additional servers, SEED provides strong confidentiality to the outsourced data. In addition, its non-interactive file encryption with support of lazy encryption greatly reduces latency in file uploading process. Security analysis and performance evaluations show the superior efficiency and effectiveness of SEED for cloud storage services.

With prevalence of remote storage services, data privacy issues become more serious owing to loss of control to outsourced data. In the meanwhile, the service providers tend to minimize storage utility costs. To minimize the storage costs while preserving data privacy, secure deduplication techniques have been proposed, which are categorized into client-side or server-side approaches. Client-side approach achieves storage and bandwidth savings at the same time but allows external adversaries to know existence of duplicates in the remote storage. On the contrary, server-side one prevents the adversaries from getting acknowledged but sacrifices network bandwidth savings. In fog computing, however, which is a new computing paradigm extending the cloud computing by outsourcing a centralized workload of the cloud to geographically distributed fog devices located at the edge of the networks, the previous deduplication schemes cannot guarantee efficiency improvement and privacy preservation simultaneously. In this paper, we present a simple but nontrivial solution of these contradictory issues in fog storage. The proposed hybrid secure deduplication protocol combines client-and server-side deduplications by taking untrustworthy fog storage environments into account. The client-side deduplication is applied in inter-network (i.e., cloud-fog network) communications to prevent network congestion at the network core, while the server-side deduplication is adopted in intra-network (i.e., user-fog network) communications to prevent information leakage via side channels for maximal data privacy. Performance and security analyses demonstrate the comparable efficiency of the proposed scheme with security enhancement.

Cloud storage provides scalable and low cost resources featuring economies of scale based on multi-tenant architecture. As the amount of data outsourced grows explosively, data deduplication, a technique that eliminates data redundancy, becomes essential. However, deduplication leads to problems with data confidentiality, thereby necessitating secure deduplication solutions. Server-aided encryption schemes have been proposed to achieve the strongest confidentiality but with the cost of managing a key server (KS). Previous schemes, however, are based on a centralized KS that uses only a single secret key assuming a single KS in the system. In cloud storage where multi-tenancy and scalability are crucial, such schemes degrade not only the effectiveness of deduplication but also the scalability with increasing users. In this paper, we extend server-aided encryption to a decentralized setting that consists of multiple KSs. The key idea of our proposed scheme is to construct an inter-KS deduplication algorithm, by which a cloud storage service provider can perform deduplication over ciphertexts from different KSs within a tenant or across tenants. This way, our scheme simultaneously offers flexibility of KS management and cross-tenant deduplication over encrypted data. The novelty of the approach is using a decentralized architecture that does not require any centralized entities for the coordination or pre-sharing of secrets among KSs. Therefore, it allows cloud storage services to offer high deduplication efficiency and scalability while preserving strong data confidentiality. We show the result of performance analysis on the proposed scheme by conducting extensive experiments. In addition, our security analysis demonstrate that the proposed scheme satisfies all desired security properties.

Attribute-based encryption (ABE) is a promising cryptographic primitive for fine-grained access control of distributed data. In ciphertext policy attribute-based encryption (CP-ABE), each user is associated with a set of attributes and data are encrypted with access policies on attributes. A user is able to decrypt a ciphertext if and only if his attributes satisfy the access policy embedded in the ciphertext. However, key escrow is inherent in ABE systems. A curious key generation center in that construction has the power to decrypt every ciphertext. We found that most of the existing ABE schemes depending on a single key authority suffer from the key escrow problem. In this study, we propose a novel CP-ABE key issuing architecture that solves the key escrow problem. The proposed scheme separates the power of issuing user keys into two parties: the key generation center and the attribute authority. In the proposed construction, the key generation center and the attribute authority issue different parts of secret key components to users through a secure two-party computation protocol such that none of them can determine the whole set of keys of users individually. We demonstrate how the proposed key issuing protocol can be applied in the existing CP-ABE scheme and resolve the key escrow problem.

The cloud storage based information retrieval service is a promising technology that will form a vigorous market in the near future. Although there have been numerous studies proposed about secure data retrieval over encrypted data in cloud services, most of them focus on providing the strict security for the data stored in a third party domain. However, those approaches require stupendous costs centralized on the cloud service provider, which could be a principal impediment to achieve efficient data retrieval in cloud storage. In this paper, we propose an efficient data retrieval scheme using attribute-based encryption. The proposed scheme is best suited for cloud storage systems with massive amount of data. It provides rich expressiveness as regards access control and fast searches with simple comparisons of searching entities. The proposed scheme also guarantees data security and user privacy during the data retrieval process.

In this paper, we propose a novel model for the appropriate recommendation of antiarrhythmic drugs by introducing a fusion of a latent semantic analysis and k-means clustering. Our model not only captures the latent factors between the types of arrhythmia and patients but also has the ability to search a group of patients with similar arrhythmias. The performance studies conducted against the MIT-BIH arrhythmia database show that clinicians accepted 66.67% of the drugs recommended from our model with a balanced f-score of 38.08%. Comparative study with previous approach also confirms the effectiveness of our model.

Mobile health (also written as mHealth) provisions the practice of public health supported by mobile devices. mHealth systems let patients and healthcare providers collect and share sensitive information, such as electronic and personal health records (EHRs) at any time, allowing more rapid convergence to optimal treatment. Key to achieving this is securely sharing data by providing enhanced access control and reliability. Typically, such sharing follows policies that depend on patient and physician preferences defined by a set of attributes. In mHealth systems, not only the data but also the policies for sharing it may be sensitive since they directly contain sensitive information which can reveal the underlying data protected by the policy. Also, since the policies usually incur linearly increasing communication costs, mHealth is inapplicable to resource-constrained environments. Lastly, access privileges may be publicly known to users, so a malicious user could illegally share his access privileges without the risk of being traced. In this paper, we propose an efficient attribute-based secure data sharing scheme in mHealth. The proposed scheme guarantees a hidden policy, constant-sized ciphertexts, and traces, with security analyses. The computation cost to the user is reduced by delegating approximately 50% of the decryption operations to the more powerful storage systems.

Broadcast and multicast services allow the high-speed delivery of multimedia content to multiple subscribers over CDMA2000 wireless networks. This relies on a high-rate broadcast packet data system with an air interface governed by two interacting protocols: the medium access control (MAC) protocol specifies the methods of multiplexing and of forward error correction used to reduce the radio link error-rate seen by the higher layers; and the security protocol specifies the procedures used to encrypt and decrypt content, following the Advanced Encryption Standard. We investigated the mutual effect of these protocols, in the context of an ARM9-based mobile platform, and their influence on delay. This allowed us to propose a novel analytic model that can predict the total delay by summing the separate but related delays incurred by implementations of the MAC and security protocols with particular parameters. This cross-layer model includes the characteristics of error control in the MAC layer and the varying condition of the fading channel in the physical layer. We can use this model to estimate the size of data buffers that mobiles require to provide a seamless multimedia service.

Broadcast encryption schemes have been studied in the past decades. Recently, insiders’ attack on the broadcast encryption scheme has been attracted attention among researchers. So, several broadcast encryption schemes with sender authentication have been proposed. However, since broadcast message size in previous schemes increases linearly at the number of target members, the previous schemes are not suitable for the group with large members. In this paper, we propose a new authenticated public key broadcast encryption scheme called ω -APKBE scheme. The proposed ω -APKBE scheme provides sender authentication property with a constant size broadcast message which is nonlinear on the number of target members. Hence, the proposed scheme is more compatible to the dynamic group with large members than the previous schemes.

The traditional security objectives of smart grids have been availability, integrity, and confidentiality. However, as the grids incorporate smart metering and load management, user and corporate privacy is increasingly becoming an issue in smart grid networks. Although transmitting current power consumption levels to the supplier or utility from each smart meter at short intervals has an advantage for the electricity supplier’s planning and management purposes, it threatens user privacy by disclosing fine-grained consumption data and usage behavior to utility providers. In this study, we propose a distributed incremental data aggregation scheme where all smart meters on an aggregation path are involved in routing the data from the source meter to the collection unit. User privacy is preserved by symmetric homomorphic encryption, which allows smart meters to participate in the aggregation without seeing any intermediate or final result. Aggregated data is further integrated with an aggregate signature to achieve data integrity and smart meter authentication in such a way that dishonest or fake smart meters cannot falsify data en route. Only the collection unit can obtain the aggregated data and verify its integrity while the individual plain data are not exposed to the collection unit. Therefore, user privacy and security are improved for the smart metering in a smart grid network.

Multicast is a scalable solution for group communications. In order to offer security for multicast applications, a group key has to be changed whenever a member joins or leaves the group. This incurs 1-affects-n problem, which is a constraint on scalability. Decentralized approaches solve the scalability problem by dividing a group into several subgroups that use independent group keys. These approaches, however, introduce new challenges: problem of trusting third party and inefficiency of data delivery. Proxy encryption is a good approach to solve the problem of trusting third party. In this paper, we propose a novel secure multicast scheme using the proxy cryptography. The proposed scheme provides not only scalability but also data transmission efficiency by dynamic subgrouping of group members while intermediate data-relaying third parties are not required to be trusted.

Key revocation is one of the most challenging and open issues in attribute-based encryption (ABE). The previous revocable ABE schemes feature a mechanism that revokes the attribute key periodically without any consideration of the user membership associated with the attribute. Thus, non-revoked users are enforced to access the key authority periodically to receive keying materials in order to update the current key. This is due to the fact that the revocation is done only on the attribute level, which results in security and scalability problems. In this paper, we propose a fine-grained user revocation scheme without affecting any non-revoked users who share the same attributes in ciphertext-policy ABE; it does not require the users to access the key authority and to update keys periodically. The proposed scheme improves the efficiency compared with previous revocable schemes and enhances the security in terms of the backward/forward secrecy on any membership changes in the ciphertext-policy ABE system. Copyright © 2011 John Wiley & Sons, Ltd.

Some of the most challenging issues in data outsourcing scenario are the enforcement of authorization policies and the support of policy updates. Ciphertext-policy attribute-based encryption is a promising cryptographic solution to these issues for enforcing access control policies defined by a data owner on outsourced data. However, the problem of applying the attribute-based encryption in an outsourced architecture introduces several challenges with regard to the attribute and user revocation. In this paper, we propose an access control mechanism using ciphertext-policy attribute-based encryption to enforce access control policies with efficient attribute and user revocation capability. The fine-grained access control can be achieved by dual encryption mechanism which takes advantage of the attribute-based encryption and selective group key distribution in each attribute group. We demonstrate how to apply the proposed mechanism to securely manage the outsourced data. The analysis results indicate that the proposed scheme is efficient and secure in the data outsourcing systems.

Efficient access control with scalable rekeying is one of the most important requirements for secure group communications, especially in a dynamic and large group. In a many-to-many group communication environment, sender authentication is also another important security requirement as each participant can potentially be both a sender and a receiver. In this study, we propose an authenticated group communication scheme which is secure against an adaptive chosen ciphertext attack using identity-based signcryption. The proposed scheme allows multiple senders to dynamically multicast messages into an arbitrary group of receivers determined by the senders. In the proposed scheme, the group member can be a stateless receiver. Data confidentiality of the group communication is guaranteed as well as the sender authentication.

Self-healing key distribution schemes for broadcast encryption are capable of recovering missed group keys and resisting a collusion attack of up to t revoked users. However, since previous schemes have been considered only m sessions, it does not suitable to support infinite sessions. In the paper, we propose an efficient δ-self healing key distribution scheme with revocation capability. The proposed scheme can support infinite sessions by updating the private key of users and supporting a partial revocation. The communication overhead of the proposed scheme is compared with several previous works.