Stronger security notions for decentralized traceable attribute-based signatures and more efficient constructions

We revisit the notion of Decentralized Traceable Attribute-Based Signatures (DTABS) introduced by El Kaafarani et al. (CT-RSA 2014) and improve the state-of-the-art in three dimensions: Firstly, we provide a new stronger security model which circumvents some shortcomings in existing models. Our model minimizes the trust placed in attribute authorities and hence provides, among other things, a stronger definition for non-frameability. In addition, our model captures the notion of tracing soundness which is important for many applications of the primitive. Secondly, we provide a generic construction that is secure w.r.t. our strong security model and show two example instantiations in the standard model which are more efficient than existing constructions (secure under weaker security definitions). Finally, we dispense with the need for the expensive zero-knowledge proofs required for proving tracing correctness by the tracing authority. As a result, tracing a signature in our constructions is significantly more efficient than existing constructions, both in terms of the size of the tracing proof and the computational cost required to generate and verify it. For instance, verifying tracing correctness in our constructions requires only 4 pairings compared to 34 pairings in the most efficient existing construction

A survey on group signature schemes

Group Signature, extension of digital signature, allows members of a group to sign messages on behalf of the group, such that the resulting signature does not reveal the identity of the signer. Any client can verify the authenticity of the document by using the public key parameters of the group. In case of dispute, only a designated group manager, because of his special property, is able to open signatures, and thus reveal the signer’s identity. Its applications are widespread, especially in e-commerce such as e-cash, e-voting and e-auction. This thesis incorporates the detailed study of various group signature schemes, their cryptographic concepts and the main contributions in this field. We implemented a popular group signature scheme based upon elliptic curve cryptosystems. Moreover, the group signature is dynamic i.e. remains valid, if some members leave the group or some new members join the group. Full traceability feature is also included in the implemented scheme. For enhanced security the the scheme implements distributed roles of the group manager. We also analysed various security features, formal models, challenges and cryptanalysis of some significant contributions in this area

Secure and Privacy-Aware Cloud-Assisted Video Reporting Service in 5G Enabled Vehicular Networks

Vehicular networks are one of the main technologies that will be leveraged by the arrival of the future fifth generation (5G) mobile cellular networks. While scalability and latency are the major drawbacks of IEEE 802.11p and 4G LTE enabled vehicular communications, respectively, the 5G technology is a promising solution to empower the real-time services offered by vehicular networks. However, the security and privacy of such services in 5G enabled vehicular networks need to be addressed first. In this paper, we propose a novel system model for a 5G enabled vehicular network that facilitates a reliable, secure and privacy-aware real-time video reporting service. This service is designed for the participating vehicles to instantly report the videos of traffic accidents to guarantee a timely response from official and/or ambulance vehicles toward accidents. While it provides strong security and privacy guarantees for the participating vehicle’s identity and the video contents, the proposed service ensures traceability of misbehaving participants through a cooperation scheme among different authorities. We show the feasibility and the fulfilment of the proposed reporting service in 5G enabled vehicular networks in terms of security, privacy and efficiency

Privacy and security protection in cloud integrated sensor networks

Wireless sensor networks have been widely deployed in many social settings to monitor human activities and urban environment. In these contexts, they acquire and collect sensory data, and collaboratively fuse the data. Due to resource constraint, sensor nodes however cannot perform complex data processing. Hence, cloud-integrated sensor networks have been proposed to leverage the cloud computing capabilities for processing vast amount of heterogeneous sensory data. After being processed, the sensory data can then be accessed and shared among authorized users and applications pervasively. Various security and privacy threats can arise when the people-centric sensory data is collected and transmitted within the sensor network or from the network to the cloud; security and privacy remain a big concern when the data is later accessed and shared among different users and applications after being processed. Extensive research has been conducted to address the security and privacy issues without sacrificing resource efficiency. Unfortunately, the goals of security/privacy protection and resource efficiency may not be easy to accomplish simultaneously, and may even be sharply contrary to each other. Our research aims to reconcile the conflicts between these goals in several important contexts. Specifically, we first investigate the security and privacy protection of sensory data being transmitted within the sensor network or from the sensor network to the cloud, which includes: (1) efficient, generic privacy preserving schemes for sensory data aggregation; (2) a privacy-preserving integrity detection scheme for sensory data aggregation; (3) an efficient and source-privacy preserving scheme for catching packet droppers and modifiers. Secondly, we further study how to address people\u27s security and privacy concerns when accessing sensory data from the cloud. To preserve privacy for sensory data aggregation, we propose a set of generic, efficient and collusion-resilient privacy-preserving data aggregation schemes. On top of these privacy preserving schemes, we also develop a scheme to simultaneously achieve privacy preservation and detection of integrity attack for data aggregation. Our approach outperforms existing solutions in terms of generality, node compromise resilience, and resource efficiency. To remove the negative effects caused by packet droppers and modifiers, we propose an efficient scheme to identify and catch compromised nodes which randomly drop packets and/or modify packets. The scheme employs an innovative packet marking techniques, with which selective packet dropping and modification can be significantly alleviated while the privacy of packet sources can be preserved. To preserve the privacy of people accessing the sensory data in the cloud, we propose a new efficient scheme for resource constrained devices to verify people\u27s access privilege without exposing their identities in the presence of outsider attacks or node compromises; to achieve the fine-grained access control for data sharing, we design privacy-preserving schemes based on users\u27 affiliated attributes, such that the access policies can be flexibly specified and enforced without involving complicated key distribution and management overhead. Extensive analysis, simulations, theoretical proofs and implementations have been conducted to evaluate the effectiveness and efficiency of our proposed schemes. The results show that our proposed schemes resolve several limitations of existing work and achieve better performance in terms of resource efficiency, security strength and privacy preservation

Privacy considerations for secure identification in social wireless networks

This thesis focuses on privacy aspects of identification and key exchange schemes for mobile social networks. In particular, we consider identification schemes that combine wide area mobile communication with short range communication such as Bluetooth, WiFi. The goal of the thesis is to identify possible security threats to personal information of users and to define a framework of security and privacy requirements in the context of mobile social networking. The main focus of the work is on security in closed groups and the procedures of secure registration, identification and invitation of users in mobile social networks. The thesis includes an evaluation of the proposed identification and key exchange schemes and a proposal for a series of modifications that augments its privacy-preserving capabilities. The ultimate design provides secure and effective identity management in the context of, and in respect to, the protection of user identity privacy in mobile social networks

Introducing Accountability to Anonymity Networks

Many anonymous communication (AC) networks rely on routing traffic through proxy nodes to obfuscate the originator of the traffic. Without an accountability mechanism, exit proxy nodes risk sanctions by law enforcement if users commit illegal actions through the AC network. We present BackRef, a generic mechanism for AC networks that provides practical repudiation for the proxy nodes by tracing back the selected outbound traffic to the predecessor node (but not in the forward direction) through a cryptographically verifiable chain. It also provides an option for full (or partial) traceability back to the entry node or even to the corresponding user when all intermediate nodes are cooperating. Moreover, to maintain a good balance between anonymity and accountability, the protocol incorporates whitelist directories at exit proxy nodes. BackRef offers improved deployability over the related work, and introduces a novel concept of pseudonymous signatures that may be of independent interest. We exemplify the utility of BackRef by integrating it into the onion routing (OR) protocol, and examine its deployability by considering several system-level aspects. We also present the security definitions for the BackRef system (namely, anonymity, backward traceability, no forward traceability, and no false accusation) and conduct a formal security analysis of the OR protocol with BackRef using ProVerif, an automated cryptographic protocol verifier, establishing the aforementioned security properties against a strong adversarial model

Versatile ABS: Usage Limited, Revocable, Threshold Traceable, Authority Hiding, Decentralized Attribute Based Signatures

In this work, we revisit multi-authority attribute based signatures (MA-ABS), and elaborate on the limitations of the current MA-ABS schemes to provide a hard to achieve (yet very useful) combination of features, i.e., decentralization, periodic usage limitation, dynamic revocation of users and attributes, reliable threshold traceability, and authority hiding. In contrast to previous work, we disallow even the authorities to de-anonymize an ABS, and only allow joint tracing by threshold-many tracing authorities. Moreover, in our solution, the authorities cannot sign on behalf of users. In this context, first we define a useful and practical attribute based signature scheme (versatile ABS or VABS) along with the necessary operations and security games to accomplish our targeted functionalities. Second, we provide the first VABS scheme in a modular design such that any application can utilize a subset of the features endowed by our VABS, while omitting the computation and communication overhead of the features that are not needed. Third, we prove the security of our VABS scheme based on standard assumptions, i.e., Strong RSA, DDH, and SDDHI, in the random oracle model. Fourth, we implement our signature generation and verification algorithms, and show that they are practical (for a VABS with 20 attributes, Sign and Verify times are below 1.2 seconds, and the generated signature size is below 0.5 MB)

Attribute-Based Signatures for Unbounded Languages from Standard Assumptions

Attribute-based signature (ABS) schemes are advanced signature schemes that simultaneously provide fine-grained authentication while protecting privacy of the signer. Previously known expressive ABS schemes support either the class of deterministic finite automata and circuits from standard assumptions or Turing machines from the existence of indistinguishability obfuscations. In this paper, we propose the first ABS scheme for a very general policy class, all deterministic Turin machines, from a standard assumption, namely, the Symmetric External Diffie-Hellman (SXDH) assumption. We also propose the first ABS scheme that allows nondeterministic finite automata (NFA) to be used as policies. Although the expressiveness of NFAs are more restricted than Turing machines, this is the first scheme that supports nondeterministic computations as policies. Our main idea lies in abstracting ABS constructions and presenting the concept of history of computations; this allows a signer to prove possession of a policy that accepts the string associated to a message in zero-knowledge while also hiding the policy, regardless of the computational model being used. With this abstraction in hand, we are able to construct ABS for Turing machines and NFAs using a surprisingly weak NIZK proof system. Essentially we only require a NIZK proof system for proving that a (normal) signature is valid. Such a NIZK proof system together with a base signature scheme are, in turn, possible from bilinear groups under the SXDH assumption, and hence so are our ABS schemes