Permanent Revocation in Attribute Based Broadcast Encryption

In this study, the authors present an efficient public-key broadcast encryption (PKBE) scheme with sub-linear size of public keys, private keys and ciphertexts and prove its adaptive security under standard assumptions. Compared with the currently best scheme of Garg et al. (CCS 2010) that provides adaptive security under standard assumptions and sub-linear size of various parameters, the ciphertext size of the author's scheme is 94% shorter and the encryption algorithm of their scheme is also 2.8 times faster than the scheme of Garg et al. To achieve their scheme, they adapt the dual system encryption technique of Waters. However, there is a challenging problem to use this technique for the construction of PKBE with sub-linear size of ciphertexts such as a tag compression problem. To overcome this problem, they first devise a novel tag update technique for broadcast encryption. Using this technique, they build an efficient PKBE scheme in symmetric bilinear groups, and prove its adaptive security under standard assumptions.

Nowadays, many organizations are adopting cloud computing for storing the large amount of organization’s important and private data. Here, it becomes important to mange appropriate access rights to these data as it is stored outside the organization’s boundary and is handled by the third party service providers. The Ciphertext Policy Attribute-based Encryption (CPABE) scheme is the most widely utilized technique that offers encrypted access control. In the existing implementations of CPABE scheme, one of the significant issues that need to be addressed is an efficient revocation mechanism. In this paper a direct and immediate user revocation approach for CPABE scheme is presented. The proposed method offers direct user revocation by maintaining the revocation list and to keep revocation list smaller the validity time is embedded in the user’s secret key. The revoked users are still able to access the previously generated ciphertexts. Hence, ciphertext update process is incorporated and a separate immediate revocation list is maintained so that the revoked users’ access is restricted. Also, in the proposed system the revocation information is embedded in ciphertext as a separate part so the update process of ciphertext is more efficient.KeywordsAttributesRevocationABECPABERevocation listValidity periodCloudAccess structure

Anonymous certificate-based broadcast encryption with constant decryption cost

Broadcast encryption is a primary technology that has been used for content protection. It enables a broadcaster to distribute content to a set of users so that only a privileged subset of users can access the content and another subset of revoked users cannot access the content. The main enabling block in a broadcast encryption scheme is the session key block, which each authorized user processes differently, but each gets the same valid session key. Currently all existing broadcast encryption schemes have assumed that the content and authorized users are equally privileged. There are emerging scenarios that demand protection for content with different privileges and for users with different privileges. In this paper we shall present a new broadcast encryption scheme that continues to employ single session key blocks but provides different privileged protections for different content and users. In particular we will expand the elegant subset-cover-based broadcast encryption scheme. We shall introduce a new concept called “security class” into the session key blocks. We use keys derived from a chain of one-way functions. Our approach is simple, efficient and secure.

Broadcast encryption is a novel concept for sending a special message to a subset of users. In broadcast encryption schemes, the distribution center broadcasts the message in encrypted form and expect that only the intended users be able to decrypt the message. This concept has several applications such as pay-per-service TVs. In this paper, we investigate one of the most recent broadcast encryption schemes and show that the introduced scheme does not provide the main requirement of broadcast encryption schemes. For this purpose, we demonstrate that all of the users, including authorized and unauthorized users, can decrypt the broadcasted encrypted message.

Ciphertext policy attribute-based encryption (CP-ABE) is a promising cryptographic technology and a key component that enable secure data sharing in a cloud environment through fine-grained access control. Since it was introduced, many interesting schemes have been proposed. However, in addition to managing data sharing through access control, a comprehensive scheme should also cater for user revocation and ciphertext queries. This is because in a cloud environment new users may join while existing users may leave the system. At the same time, given the potentially large amount of data stored in a cloud storage, user should be able to retrieve the required files efficiently in a privacy-preserving manner. To address the above issue, in this paper, we propose a practical searchable CP-ABE scheme supporting user revocation. In contrast to existing schemes that provide only single keyword query, our efficient search function provides conjunctive search, which allows user to locate a ciphertext related to a set of keywords. The computation overhead of our user revocation is at least on par with existing schemes. Besides, the security analysis indicates that the proposed scheme is secure under the decisional Bilinear Diffie-Hellman assumption. We also provide extensive experimental results to confirm the efficiency and feasibility of our proposed construction.

The task of searchable encryption schemes in multi-user setting is to handle the problem of dynamical user injection and revocation with consideration of feasibility. Especially, we have to make sure that user revocation will not cause security problem, such as leakage of secret key. Recently, fine-grained access control using trusted third party is proposed to resolve this issue. However, it increases the management complexity for maintaining massive authentication information of users. We present a new concept of coarse-grained access control for the first time and use it to construct a multi-user searchable encryption model in hybrid cloud. In our construction, there are two typical schemes, one is broadcast encryption (BE) scheme to simplify access control, the other is a single-user searchable encryption scheme, which supports two-phases operation and is secure when untrustful server colludes with the adversary. Moreover, we implement such a practical scheme using an improved searchable symmetric encryption scheme, and security analysis support our scheme.

RETRACTED: A public key size homomorphic encryption scheme based on the sum of sparse subsets and integers

MLPPT-MHS: Multi-Layered Privacy Preserving and Traceable Mobile Health System

Public-key encryption is extensively used to provide digital data confidentiality and deliver the security features, such as nonrepudiation (digital signature) and secure key exchange. Conventional public-key schemes are based on mathematical problems with inflexible constraints, and the security of digital contents relies on computational complexity. In the era of emerging technologies, most public-key image encryption schemes are susceptible to various threats. We propose a novel public-key encryption in this article with near-ring criteria and provide confidentiality to private data with the microstates of the Einstein crystal model. The virtual oscillator generated by microstates of initial oscillators for the common secrets with the public-key scheme produces unique states to encrypt digital data. The privacy-preserved structure, that mimics the data stream of digital content with the behavior of the improved Einstein crystal model, describes a system in terms of microstates to generate diffusion in the plain data with unique states of a virtual oscillator. The performance and digital forensic evaluations, such as randomness, histogram uniformity, pixels’ correlation, pixels’ similarity, visual strength, pixels’ incongruity, key sensitivity, linear and differential attacks, noise, and occlusion attacks analyses, certify the resistivity of the proposed algorithm against potential threats and provide superior capacity in comparison to existing methodologies to hostile certain attacks.

Broadcast encryption is a cryptographic primitive that allows a sender to securely transmit a message to a set of receivers. The most influential broadcast encryption system was proposed in 2001 by Naor, Naor, Lotspiech, based on binary trees and the Subset Difference (SD) method. In 2006, Jang, Nyang, and Song suggested a new broadcast encryption system that can reduce transmission rate by 50% compared to the SD method, by introducing the so-called '2-SD' method. Their result was later given the registration of a patent in Korea (registration number: 100879083). Unfortunately, however, this paper shows that Jang et. al.'s broadcast encryption system is not secure against collusion attacks that are considered as being the basic security requirement in designing broadcast encryption.

A Cluster of CP-ABE Microservices for VANET

A revocable and comparable attribute-based signature scheme from lattices for IoMT

The first practical public-key encryption scheme and digital signature scheme were proposed in 1978 by Rivest et al. [165]. While the original public-key encryption scheme would not be considered secure by modern standards, the RSARSA transform has been the basis of dozens of public-key encryption schemes and digital signature schemes. These schemes have proven very successful and have been very widely deployed in industry. However, despite being widely used in the design of public-key encryption and digital signature schemes, the RSARSA transform has not been widely used in the construction of signcryption schemes.

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.