Privacy-preserving PKI design based on group signature

Nowadays, Internet becomes a part of our life. We can make use of numerous services with personal computer, Lap-top, tablet, smart phone or smart TV. These devices with network make us enjoy ubiquitous computing life. Sometimes, on-line services request us authentication or identification for access control and authorization, and PKI technology is widely used because of its security. However the possibility of privacy invasion will increase, if We’re identified with same certificate in many services and these identification data are accumulated. For privacy-preserving authentication or anonymous authentication, there have been many researches such as Group signatures, anonymous credentials, etc. Among these researches, group signatures are very practical Because they provide unlinkability and traceability as well as anonymity. In this paper, we propose a privacy-preserving PKI based on group signature, with which users’ privacy can be Kept in services. Because of traceability, their identities can be traced if they abuse anonymity such as cybercrime. Moreover, we will also discuss open issues for further studies

Linking-Based Revocation for Group Signatures: A Pragmatic Approach for Efficient Revocation Checks

Group signature schemes (GSS) represent an important privacy-enhancing technology. However, their practical applicability is restricted due to inefficiencies of existing membership revocation mechanisms that often place a too large computational burden and communication overhead on the involved parties. Moreover, it seems that the general belief (or unwritten law) of avoiding online authorities by all means artificially and unnecessarily restricts the efficiency and practicality of revocation mechanisms in GSSs. While a mindset of preventing online authorities might have been appropriate more than 10 years ago, today the availability of highly reliable cloud computing infrastructures could be used to solve open challenges. More specifically, in order to overcome the inefficiencies of existing revocation mechanisms, we propose an alternative approach denoted as linking-based revocation (LBR) which is based on the concept of controllable linkability. The novelty of LBR is its transparency for signers and verifiers that spares additional computations as well as updates. We therefore introduce dedicated revocation authorities (RAs) that can be contacted for efficient (constant time) revocation checks. In order to protect these RAs and to reduce the trust in involved online authorities, we additionally introduce distributed controllable linkability. Using latter, RAs cooperate with multiple authorities to compute the required linking information, thus reducing the required trust. Besides efficiency, an appealing benefit of LBR is its generic applicability to pairing-based GSSs secure in the BSZ model as well as GSSs with controllable linkability. This includes the XSGS scheme, and the GSSs proposed by Hwang et al., one of which has been standardized in the recent ISO 20008-2 standard

Privacy Preserving Cryptographic Protocols for Secure Heterogeneous Networks

Disertační práce se zabývá kryptografickými protokoly poskytující ochranu soukromí, které jsou určeny pro zabezpečení komunikačních a informačních systémů tvořících heterogenní sítě. Práce se zaměřuje především na možnosti využití nekonvenčních kryptografických prostředků, které poskytují rozšířené bezpečnostní požadavky, jako je například ochrana soukromí uživatelů komunikačního systému. V práci je stanovena výpočetní náročnost kryptografických a matematických primitiv na různých zařízeních, které se podílí na zabezpečení heterogenní sítě. Hlavní cíle práce se zaměřují na návrh pokročilých kryptografických protokolů poskytujících ochranu soukromí. V práci jsou navrženy celkově tři protokoly, které využívají skupinových podpisů založených na bilineárním párování pro zajištění ochrany soukromí uživatelů. Tyto navržené protokoly zajišťují ochranu soukromí a nepopiratelnost po celou dobu datové komunikace spolu s autentizací a integritou přenášených zpráv. Pro navýšení výkonnosti navržených protokolů je využito optimalizačních technik, např. dávkového ověřování, tak aby protokoly byly praktické i pro heterogenní sítě.The dissertation thesis deals with privacy-preserving cryptographic protocols for secure communication and information systems forming heterogeneous networks. The thesis focuses on the possibilities of using non-conventional cryptographic primitives that provide enhanced security features, such as the protection of user privacy in communication systems. In the dissertation, the performance of cryptographic and mathematic primitives on various devices that participate in the security of heterogeneous networks is evaluated. The main objectives of the thesis focus on the design of advanced privacy-preserving cryptographic protocols. There are three designed protocols which use pairing-based group signatures to ensure user privacy. These proposals ensure the protection of user privacy together with the authentication, integrity and non-repudiation of transmitted messages during communication. The protocols employ the optimization techniques such as batch verification to increase their performance and become more practical in heterogeneous networks.

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)

Foundations of Fully Dynamic Group Signatures

Group signatures allow members of a group to anonymously sign on behalf of the group. Membership is administered by a designated group manager. The group manager can also reveal the identity of a signer if and when needed to enforce accountability and deter abuse. For group signatures to be applicable in practice, they need to support fully dynamic groups, i.e., users may join and leave at any time. Existing security definitions for fully dynamic group signatures are informal, have shortcomings, and are mutually incompatible. We fill the gap by providing a formal rigorous security model for fully dynamic group signatures. Our model is general and is not tailored toward a specific design paradigm and can therefore, as we show, be used to argue about the security of different existing constructions following different design paradigms. Our definitions are stringent and when possible incorporate protection against maliciously chosen keys. We consider both the case where the group management and tracing signatures are administered by the same authority, i.e., a single group manager, and also the case where those roles are administered by two separate authorities, i.e., a group manager and an opening authority. We also show that a specialization of our model captures existing models for static and partially dynamic schemes. In the process, we identify a subtle gap in the security achieved by group signatures using revocation lists. We show that in such schemes new members achieve a slightly weaker notion of traceability. The flexibility of our security model allows to capture such relaxation of traceability

Data Auditing and Security in Cloud Computing: Issues, Challenges and Future Directions

Cloud computing is one of the significant development that utilizes progressive computational power and upgrades data distribution and data storing facilities. With cloud information services, it is essential for information to be saved in the cloud and also distributed across numerous customers. Cloud information repository is involved with issues of information integrity, data security and information access by unapproved users. Hence, an autonomous reviewing and auditing facility is necessary to guarantee that the information is effectively accommodated and used in the cloud. In this paper, a comprehensive survey on the state-of-art techniques in data auditing and security are discussed. Challenging problems in information repository auditing and security are presented. Finally, directions for future research in data auditing and security have been discussed

Data auditing and security in cloud computing: issues, challenges and future directions

Cloud computing is one of the significant development that utilizes progressive computational power and upgrades data distribution and data storing facilities. With cloud information services, it is essential for information to be saved in the cloud and also distributed across numerous customers. Cloud information repository is involved with issues of information integrity, data security and information access by unapproved users. Hence, an autonomous reviewing and auditing facility is necessary to guarantee that the information is effectively accommodated and used in the cloud. In this paper, a comprehensive survey on the state-of-art techniques in data auditing and security are discussed. Challenging problems in information repository auditing and security are presented. Finally, directions for future research in data auditing and security have been discusse