Abstract This paper presents the first attribute-based signature () scheme supporting signing policies representable by Turing machines (), based on well-studied computational assumptions. Our work supports arbitrarys as signing policies in the sense that the s can accept signing attribute strings of unbounded polynomial length and there is no limit on their running time, description size, or space complexity. Moreover, we are able to achieve input-specific running time for the signing algorithm. All other known expressive schemes could at most support signing policies realizable by either arbitrary polynomial-size circuits or s having a pre-determined upper bound on the running time. Consequently, those schemes can only deal with signing attribute strings whose lengths are a priori bounded, as well as suffers from the worst-case running time problem. On a more positive note, for the first time in the literature, the signature size of our scheme only depends on the size of the signed message and is completely independent of the size of the signing policy under which the signature is generated. This is a significant achievement from the point of view of communication efficiency. Our construction makes use of indistinguishability obfuscation () for polynomial-size circuits and certain -compatible cryptographic tools. Note that, all of these building blocks including for polynomial-size circuits are currently known to be realizable under well-studied computational assumptions.

Abstract A nominative signature (NS) is a cryptographic primitive where two parties collude to produce a signature. It is a user certification system and has applications in a variety of sectors where nominee cannot trust heavily on the nominator to validate the nominee's certificate and only targeted entities are allowed to verify the signature on sensitive data. A new construction for NS from standard assumptions on lattice is provided. The authors’ construction relies on collision‐resistant preimage sampleable function and symmetric key primitives like collision‐resistant pseudorandom function and zero knowledge proof system ZKB ++ for Boolean circuits. The authors provide detailed security analysis and show that their construction achieves security under unforgeability , invisibility , impersonation , and non‐repudiation in the existing model. Furthermore, our construction exhibits non‐transferability . The security under non‐repudiation is achieved in the quantum random oracle model using Unruh transform to ZKB ++ .

In 1 the authorship was originally shown as “Ashok Kumar Das, Dheerendra Mishra and Sourav Mukhopadhyay”. This has now been corrected to “Dheerendra Mishra, Ashok Kumar Das and Sourav Mukhopadhyay”. We apologize for any inconvenience caused.

Abstract Internet‐based content distribution facilitates an efficient platform to sell the digital content to the remote users. However, the digital content can be easily copied and redistributed over the network, which causes huge loss to the right holders. On the contrary, the digital rights management (DRM) systems have been introduced in order to regulate authorized content distribution. Enterprise DRM (E‐DRM) system is an application of DRM technology, which aims to prevent illegal access of data in an enterprise. Earlier works on E‐DRM do not address anonymity, which may lead to identity theft. Recently, Chang et al. proposed an efficient E‐DRM mechanism. Their scheme provides greater efficiency and protects anonymity. Unfortunately, we identify that their scheme does not resist the insider attack and password‐guessing attack. In addition, Chang et al.'s scheme has some design flaws in the authorization phase. We then point out the requirements of E‐DRM system and present the cryptanalysis of Chang et al.'s scheme. In order to remedy the security weaknesses found in Chang et al.'s scheme, we aim to present a secure and efficient E‐DRM scheme. The proposed scheme supports the authorized content key distribution and satisfies the desirable security attributes. Additionally, our scheme offers low communication and computation overheads and user's anonymity as well. Through the rigorous formal and informal security analyses, we show that our scheme is secure against possible known attacks. Furthermore, the simulation results for the formal security analysis using the widely accepted Automated Validation of Internet Security Protocols and Applications tool ensure that our scheme is also secure. Copyright © 2015 John Wiley & Sons, Ltd.

A self-healing key distribution scheme enables a large group of users (sensor nodes) to establish a session key dynamically over an unreliable, or lossy wireless network. The main property of self-healing ensures that the qualified users can recover the lost session keys on their own from the broadcast packets and some private information, without any additional communication with the group manager, thus decreasing the load on the group manager. The only requirement for a user to recover the lost session keys, is its membership in the group both before and after the sessions in which the broadcast packets containing the keys are sent. Self-healing approach of key distribution is stateless in the sense that a user who has been off-line for some period is able to recover the lost session keys immediately after coming back on-line. This paper presents a new self-healing key distribution scheme with revocation capability that requires constant storage of personal keys for each user and we feel, it is more efficient than the previous schemes in terms of communication complexity. The novelty of this scheme is to use a different and more efficient self-healing mechanism compared to the ones in the literature. The scheme is supported by a proper security analysis in an appropriate security model. It is unconditionally secure and achieves both forward and backward secrecy. Moreover, unlike previous works, proposed self-healing key distribution is not restricted to m sessions in Setup phase.

In this paper, we develop and analyze a new self-healing key distribution scheme with revocation capability, scalable to very large groups in unreliable ad hoc wireless environment. The main emphasis of our proposed scheme is that it has significant improvement in terms of both storage and communication overhead compared to the previous works. The storage overhead of our self-healing key distribution with t revocation capability is O((t + 1) log q), and the communication complexity is O((t+1+j) log q), where q is a large prime and j is the current session number. In contrast to the previous schemes, we use a different and more efficient self-healing technique. On a more positive note, our scheme enables reuse of personal key of a user to next m sessions and consequently, overcomes the restriction of m sessions in setup phase, unlike previous works. Moreover, we analyze our scheme in an appropriate security framework and proved that it is unconditionally secure and achieves both forward secrecy and backward secrecy.

Time-memory trade-off (TMTO) is a twenty five years old technique for inverting one-way functions. The most feasible implementation of TMTO is in special purpose hardware. Till date the work on hardware architecture for TMTO has been somewhat sketchy. In this paper, we describe a systematic architecture for implementing TMTO. We break down the offline and online phases into simpler tasks and identify opportunities for pipelining and parallelism. This results in a sufficiently detailed top-level architecture. To the best of our knowledge, such architecture does not appear in the literature