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.

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

SMS based m-commerce: Meeting application and security requirements

This paper outlines the potential of SMS Based financial information and transaction services which can help users in account access, payments and in making time and location independent transactions.So far, existing m-commerce initiatives have focused on GPRS or SIM based approaches which have their specific limitations.After highlighting comparative strengths of SMS based m-commerce solutions vis a vis GPRS and SIM Based solutions the vulnerabilities of SMS technology are brought out in detail.Having outlined the security and application requirements for an m-commerce solution this paper details how Secure SMS based notification and transaction system meets these requirements

Mobile e-commerce: study and model generation, implementation issues and analysis

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Authentication Protocols and Privacy Protection

Tato dizertační práce se zabývá kryptografickými prostředky pro autentizaci. Hlavním tématem však nejsou klasické autentizační protokoly, které nabízejí pouze ověření identity, ale tzv. atributové autentizační systémy, pomocí kterých mohou uživatelé prokazovat svoje osobní atributy. Tyto atributy pak mohou představovat jakékoliv osobní informace, např. věk, národnost či místo narození. Atributy mohou být prokazovány anonymně a s podporou mnoha funkcí na ochranu digitální identity. Mezi takové funkce patří např. nespojitelnost autentizačních relací, nesledovatelnost, možnost výběru prokazovaných atributů či efektivní revokace. Atributové autentizační systémy jsou již nyní považovány za nástupce současných systémů v oficiálních strategických plánech USA (NSTIC) či EU (ENISA). Část požadovaných funkcí je již podporována existujícími kryptografickými koncepty jako jsou U-Prove či idemix. V současné době však není známý systém, který by poskytoval všechny potřebné funkce na ochranu digitální identity a zároveň byl prakticky implementovatelný na zařízeních, jako jsou čipové karty. Mezi klíčové slabiny současných systémů patří především chybějící nespojitelnost relací a absence revokace. Není tak možné efektivně zneplatnit zaniklé uživatele, ztracené či ukradené autentizační karty či karty škodlivých uživatelů. Z těchto důvodů je v této práci navrženo kryptografické schéma, které řeší slabiny nalezené při analýze existujících řešení. Výsledné schéma, jehož návrh je založen na ověřených primitivech, jako jsou $\Sigma$-protokoly pro důkazy znalostí, kryptografické závazky či ověřitelné šifrování, pak podporuje všechny požadované vlastnosti pro ochranu soukromí a digitální identity. Zároveň je však návrh snadno implementovatelný v prostředí smart-karet. Tato práce obsahuje plný kryptografický návrh systému, formální ověření klíčových vlastností, matematický model schématu v programu Mathematica pro ověření funkčnosti a výsledky experimentální implementace v prostředí .NET smart-karet. I přesto, že navrhovaný systém obsahuje podporu všech funkcí na ochranu soukromí, včetně těch, které chybí u existujících systémů, jeho výpočetní složitost zůstává stejná či nižší, doba ověření uživatele je tedy kratší než u existujících systémů. Výsledkem je schéma, které může velmi znatelně zvýšit ochranu soukromí uživatelů při jejich ověřování, především při využití v elektronických dokladech, přístupových systémech či Internetových službách.This dissertation thesis deals with the cryptographic constructions for user authentication. Rather than classical authentication protocols which allow only the identity verification, the attribute authentication systems are the main topic of this thesis. The attribute authentication systems allow users to give proofs about the possession of personal attributes. These attributes can represent any personal information, for example age, nationality or birthplace. The attribute ownership can be proven anonymously and with the support of many features for digital identity protection. These features include, e.g., the unlinkability of verification sessions, untraceability, selective disclosure of attributes or efficient revocation. Currently, the attribute authentication systems are considered to be the successors of existing authentication systems by the official strategies of USA (NSTIC) and EU (ENISA). The necessary features are partially provided by existing cryptographic concepts like U-Prove and idemix. But at this moment, there is no system providing all privacy-enhancing features which is implementable on computationally restricted devices like smart-cards. Among all weaknesses of existing systems, the missing unlinkability of verification sessions and the absence of practical revocation are the most critical ones. Without these features, it is currently impossible to invalidate expired users, lost or stolen authentication cards and cards of malicious users. Therefore, a new cryptographic scheme is proposed in this thesis to fix the weaknesses of existing schemes. The resulting scheme, which is based on established primitives like $\Sigma$-protocols for proofs of knowledge, cryptographic commitments and verifiable encryption, supports all privacy-enhancing features. At the same time, the scheme is easily implementable on smart-cards. This thesis includes the full cryptographic specification, the formal verification of key properties, the mathematical model for functional verification in Mathematica software and the experimental implementation on .NET smart-cards. Although the scheme supports all privacy-enhancing features which are missing in related work, the computational complexity is the same or lower, thus the time of verification is shorter than in existing systems. With all these features and properties, the resulting scheme can significantly improve the privacy of users during their verification, especially when used in electronic ID systems, access systems or Internet services.

A Unlinkable Delegation-based Authentication Protocol with Users’ Non-repudiation for Portable Communication Systems

[[abstract]]For portable communication systems, the delegation-based authentication protocol provides efficient subsequent login authentication, data confidentiality, user privacy protection, and non-repudiation. However, in all proposed protocols, the non-repudiation of mobile users is based on an unreasonable assumption that home location registers are always trusted. To weaken this assumption and enhance the nonrepudiation of mobile users, a new delegation-based authentication protocol is proposed. The new protocol also removes the exhaustive search problem of the subsequent login authentication to improve the subsequent login authentication performance. Moreover, the user unlinkability in the subsequent login authentication is also provided to enhance the user identity privacy protection.[[incitationindex]]EI[[incitationindex]]CEPS[[booktype]]紙

Backward Unlinkability for a VLR Group Signature Scheme with Efficient Revocation Check

Verifier-Local Revocation (VLR) group signatures, introduced by Boneh and Shacham in 2004, are a particular case of dynamic group signature schemes where the revocation process does not influence the activity of the signers. The verifiers use a Revocation List to check if the signers are revoked. In all known schemes, checking a signature requires a computational time linear in the number of revoked members. Usually, it requires one pairing per revoked user. Recently, Chen and Li proposed a scheme where Revocation Check uses exponentiations instead of pairings. In this paper, we first propose a correction of their scheme to enable a full proof of the traceability property. Then our main contribution is to extend this tweaked scheme to ensure Backward Unlinkability. This important property prevents the loss of anonymity of past signatures when a user is revoked. We succeed in achieving this consequent improvement with a constant additional cost only. We thus obtain the scheme with the most efficient Revocation Check among VLR schemes enabling Backward Unlinkability

Cooperating broadcast and cellular conditional access system for digital television

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The lack of interoperability between Pay‐TV service providers and a horizontally integrated business transaction model have compromised the competition in the Pay‐TV market. In addition, the lack of interactivity with customers has resulted in high churn rate and improper security measures have contributed into considerable business loss. These issues are the main cause of high operational costs and subscription fees in the Pay‐TV systems. This paper presents a novel end‐to‐end system architecture for Pay‐TV systems cooperating mobile and broadcasting technologies. It provides a cost‐effective, scalable, dynamic and secure access control mechanism supporting converged services and new business opportunities in Pay‐TV systems. It enhances interactivity, security and potentially reduces customer attrition and operational cost. In this platform, service providers can effectively interact with their customers, personalise their services and adopt appropriate security measures. It breaks up the rigid relationship between a viewer and set‐top box as imposed by traditional conditional access systems, thus, a viewer can fully enjoy his entitlements via an arbitrary set‐top box. Having thoroughly considered state‐of‐the‐art technologies currently being used across the world, the thesis highlights novel use cases and presents the full design and implementation aspects of the system. The design section is enriched by providing possible security structures supported thereby. A business collaboration structure is proposed, followed by a reference model for implementing the system. Finally, the security architectures are analysed to propose the best architecture on the basis of security, complexity and set‐top box production cost criteria