/pdf/a-break-in-the-clouds-towards-a-cloud-definition-svovsw1r5a.pdf

A Break in the Clouds: Towards a Cloud Definition

An important open problem in the area of Traitor Tracing is designing a scheme with constant expansion of the size of keys (users' keys and the encryption key) and of the size of ciphertexts with respect to the size of the plaintext. This problem is known from the introduction of Traitor Tracing by Chor, Fiat and Naor. We refer to such schemes as traitor tracing with constant transmission rate. Here we present a general methodology and two protocol constructions that result in the first two public-key traitor tracing schemes with constant transmission rate in settings where plaintexts can be calibrated to be sufficiently large. Our starting point is the notion of copyrighted function which was presented by Naccache, Shamir and Stern. We first solve the open problem of discrete-log-based and public-key-based copyrighted function. Then, we observe the simple yet crucial relation between (public-key) copyrighted encryption and (public-key) traitor tracing, which we exploit by introducing a generic design paradigm for designing constant transmission rate traitor tracing schemes based on copyrighted encryption functions. Our first scheme achieves the same expansion efficiency as regular ElGamal encryption. The second scheme introduces only a slightly larger (constant) overhead, however, it additionally achieves efficient black-box traitor tracing (against any pirate construction).

Traitor Tracing with constant transmission rate

In a world where the industry of mobile applications is continuously expanding and new health care apps and devices are created every day, it is important to take special care of the collection and treatment of users' personal health information. However, the appropriate methods to do this are not usually taken into account by apps designers and insecure applications are released. This paper presents a study of security and privacy in mHealth, focusing on three parts: a study of the existing laws regulating these aspects in the European Union and the United States, a review of the academic literature related to this topic, and a proposal of some recommendations for designers in order to create mobile health applications that satisfy the current security and privacy legislation. This paper will complement other standards and certifications about security and privacy and will suppose a quick guide for apps designers, developers and researchers.

Privacy and Security in Mobile Health Apps: A Review and Recommendations

Secure sharing of Personal Health Records in cloud computing

Personal Health Records (PHRs) should remain the lifelong property of patients, who should be able to show them conveniently and securely to selected caregivers and institutions. In this paper, we present My PHR Machines, a cloud-based PHR system taking a radically new architectural solution to health record portability. In My PHR Machines, health-related data and the application software to view and/or analyze it are separately deployed in the PHR system. After uploading their medical data to My PHR Machines, patients can access them again from remote virtual machines that contain the right software to visualize and analyze them without any need for conversion. Patients can share their remote virtual machine session with selected caregivers, who will need only a Web browser to access the pre-loaded fragments of their lifelong PHR. We discuss a prototype of My PHR Machines applied to two use cases, i.e., radiology image sharing and personalized medicine.

Scalable and Secure Sharing of Personal Health Records in Cloud Computing using Attribute–Based Encryption

The telecare medicine information system enables or supports health-care delivery services. In order to safeguard patients' privacy, such as telephone number, medical record number, health information, etc., a secure authentication scheme will thus be in demand. Recently, Wu et al. proposed a smart card based password authentication scheme for the telecare medicine information system. Later, He et al. pointed out that Wu et al.'s scheme could not resist impersonation attacks and insider attacks, and then presented a new scheme. In this paper, we show that both of them fail to achieve two-factor authentication as smart card based password authentication schemes should achieve. We also propose an improved authentication scheme for the telecare medicine information system, and demonstrate that the improved one satisfies the security requirements of two-factor authentication and is also efficient.

An Improved Authentication Scheme for Telecare Medicine Information Systems

Cloud computing provides a flexible and convenient way for data sharing, which brings various benefits for both the society and individuals. But there exists a natural resistance for users to directly outsource the shared data to the cloud server since the data often contain valuable information. Thus, it is necessary to place cryptographically enhanced access control on the shared data. Identity-based encryption is a promising cryptographical primitive to build a practical data sharing system. However, access control is not static. That is, when some user's authorization is expired, there should be a mechanism that can remove him/her from the system. Consequently, the revoked user cannot access both the previously and subsequently shared data. To this end, we propose a notion called revocable-storage identity-based encryption (RS-IBE), which can provide the forward/backward security of ciphertext by introducing the functionalities of user revocation and ciphertext update simultaneously. Furthermore, we present a concrete construction of RS-IBE, and prove its security in the defined security model. The performance comparisons indicate that the proposed RS-IBE scheme has advantages in terms of functionality and efficiency, and thus is feasible for a practical and cost-effective data-sharing system. Finally, we provide implementation results of the proposed scheme to demonstrate its practicability.

Secure Data Sharing in Cloud Computing Using Revocable-Storage Identity-Based Encryption

Cloud storage facilitates both individuals and enterprises to cost effectively share their data over the Internet. However, this also brings difficult challenges to the access control of shared data since few cloud servers can be fully trusted. Ciphertext-policy attribute-based encryption (CP-ABE) is a promising approach that enables the data owners themselves to place fine-grained and cryptographically-enforced access control over outsourced data. In this paper, we present secure and cost-effective attribute-based data access control for cloud storage systems. Specifically, we construct a multiauthority CP-ABE scheme that features: 1) the system does not need a fully trusted central authority, and all attribute authorities independently issue secret keys for users; 2) each attribute authority can dynamically remove any user from its domain such that those revoked users cannot access subsequently outsourced data; 3) cloud servers can update the encrypted data from the current time period to the next one such that the revoked users cannot access those previously available data; and 4) the update of secret keys and ciphertext is performed in a public way. We show the merits of our scheme by comparing it with the related works, and further implement it to demonstrate its practicality. In addition, the proposed scheme is proven secure in the random oracle model.

Secure and Efficient Attribute-Based Access Control for Multiauthority Cloud Storage

A multi-server authentication scheme enables a remote user to access the services provided by multiple servers after registering with the registration center. Recently, Pippal et al. (Wirel Pers Commun 2013, doi: 10.1007/s11277-013-1039-6 ) introduced a robust smart card authentication scheme for multi-server architecture. They also illustrated that their scheme could be free from potential network attacks, and validated the scheme by using BAN logic. In this paper, by presenting concrete attacks, we demonstrate that Pippal et al.'s scheme can not withstand off-line password guessing attacks, impersonation attacks and privileged insider attacks. Furthermore, to overcome these attacks, we propose an improved authentication scheme for multi-server architecture using smart card and password. Security and efficiency analysis indicates that our scheme not only actually achieves intended security goals (e.g., two-factor authentication, perfect forward secrecy etc.), but also is efficient enough to be implemented for practical applications.

Cryptanalysis and Improvement of a Robust Smart Card Authentication Scheme for Multi-server Architecture

In distributed systems, the smart card based password authentication, as one of the most convenient and efficient two-factor authentication mechanisms, is widely used to ensure that the protected services are not available to unauthorized users Recently, Li et al demonstrated that the smart card based password authentication scheme proposed by Chen et al cannot provide perfect forward secrecy as they claimed In addition, the password change phase of the scheme is unfriendly and inefficient Sub-sequently, Li et al presented an enhanced smart card based password authentication scheme to overcome the above flaws existing in Chen et al's scheme Further-more, Kumari and Khan, and Jiang et al demonstrated that Chen et al's scheme cannot resist off-line password guessing attacks, and also proposed an improved scheme, respectively In this study, we first illustrate that Li et al's scheme, and Kumari and Khan's scheme both fail to achieve the basic security requirement of the smart card based password authentication, namely, once the private information stored in the smart card has been extracted, the schemes would be vulnerable to off-line password guessing attacks We also point out that Jiang et al's scheme, as well as Kumari and Khan's scheme can- not provide perfect forward secrecy Then, we introduce a new smart card based password authentication scheme By presenting concrete analysis of security and performance, we show that the proposed scheme cannot only resist various well-known attacks, but also is more efficient than other related works, and thus is feasible for practical applications

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Wenfen Liu

Papers

An Improved Authentication Scheme for Telecare Medicine Information Systems

Secure Data Sharing in Cloud Computing Using Revocable-Storage Identity-Based Encryption

Secure and Efficient Attribute-Based Access Control for Multiauthority Cloud Storage

Cryptanalysis and Improvement of a Robust Smart Card Authentication Scheme for Multi-server Architecture

Secure and Efficient Smart Card Based Remote User Password Authentication Scheme