EFFICIENT AND SCALABLE NETWORK SECURITY PROTOCOLS BASED ON LFSR SEQUENCES

The gap between abstract, mathematics-oriented research in cryptography and the engineering approach of designing practical, network security protocols is widening. Network researchers experiment with well-known cryptographic protocols suitable for different network models. On the other hand, researchers inclined toward theory often design cryptographic schemes without considering the practical network constraints. The goal of this dissertation is to address problems in these two challenging areas: building bridges between practical network security protocols and theoretical cryptography. This dissertation presents techniques for building performance sensitive security protocols, using primitives from linear feedback register sequences (LFSR) sequences, for a variety of challenging networking applications. The significant contributions of this thesis are: 1. A common problem faced by large-scale multicast applications, like real-time news feeds, is collecting authenticated feedback from the intended recipients. We design an efficient, scalable, and fault-tolerant technique for combining multiple signed acknowledgments into a single compact one and observe that most signatures (based on the discrete logarithm problem) used in previous protocols do not result in a scalable solution to the problem. 2. We propose a technique to authenticate on-demand source routing protocols in resource-constrained wireless mobile ad-hoc networks. We develop a single-round multisignature that requires no prior cooperation among nodes to construct the multisignature and supports authentication of cached routes. 3. We propose an efficient and scalable aggregate signature, tailored for applications like building efficient certificate chains, authenticating distributed and adaptive content management systems and securing path-vector routing protocols. 4. We observe that blind signatures could form critical building blocks of privacypreserving accountability systems, where an authority needs to vouch for the legitimacy of a message but the ownership of the message should be kept secret from the authority. We propose an efficient blind signature that can serve as a protocol building block for performance sensitive, accountability systems. All special forms digital signatures—aggregate, multi-, and blind signatures—proposed in this dissertation are the first to be constructed using LFSR sequences. Our detailed cost analysis shows that for a desired level of security, the proposed signatures outperformed existing protocols in computation cost, number of communication rounds and storage overhead

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.

Cryptographic Schemes based on Elliptic Curve Pairings

This thesis introduces the concept of certificateless public key cryptography (CLPKC). Elliptic curve pairings are then used to make concrete CL-PKC schemes and are also used to make other efficient key agreement protocols. CL-PKC can be viewed as a model for the use of public key cryptography that is intermediate between traditional certificated PKC and ID-PKC. This is because, in contrast to traditional public key cryptographic systems, CL-PKC does not require the use of certificates to guarantee the authenticity of public keys. It does rely on the use of a trusted authority (TA) who is in possession of a master key. In this respect, CL-PKC is similar to identity-based public key cryptography (ID-PKC). On the other hand, CL-PKC does not suffer from the key escrow property that is inherent in ID-PKC. Applications for the new infrastructure are discussed. We exemplify how CL-PKC schemes can be constructed by constructing several certificateless public key encryption schemes and modifying other existing ID based schemes. The lack of certificates and the desire to prove the schemes secure in the presence of an adversary who has access to the master key or has the ability to replace public keys, requires the careful development of new security models. We prove that some of our schemes are secure, provided that the Bilinear Diffie-Hellman Problem is hard. We then examine Joux’s protocol, which is a one round, tripartite key agreement protocol that is more bandwidth-efficient than any previous three-party key agreement protocol, however, Joux’s protocol is insecure, suffering from a simple man-in-the-middle attack. We show how to make Joux’s protocol secure, presenting several tripartite, authenticated key agreement protocols that still require only one round of communication. The security properties of the new protocols are studied. Applications for the protocols are also discussed

Secure Authentication and Privacy-Preserving Techniques in Vehicular Ad-hoc NETworks (VANETs)

In the last decade, there has been growing interest in Vehicular Ad Hoc NETworks (VANETs). Today car manufacturers have already started to equip vehicles with sophisticated sensors that can provide many assistive features such as front collision avoidance, automatic lane tracking, partial autonomous driving, suggestive lane changing, and so on. Such technological advancements are enabling the adoption of VANETs not only to provide safer and more comfortable driving experience but also provide many other useful services to the driver as well as passengers of a vehicle. However, privacy, authentication and secure message dissemination are some of the main issues that need to be thoroughly addressed and solved for the widespread adoption/deployment of VANETs. Given the importance of these issues, researchers have spent a lot of effort in these areas over the last decade. We present an overview of the following issues that arise in VANETs: privacy, authentication, and secure message dissemination. Then we present a comprehensive review of various solutions proposed in the last 10 years which address these issues. Our survey sheds light on some open issues that need to be addressed in the future

Efficient cryptographic primitives: Secure comparison, binary decomposition and proxy re-encryption

”Data outsourcing becomes an essential paradigm for an organization to reduce operation costs on supporting and managing its IT infrastructure. When sensitive data are outsourced to a remote server, the data generally need to be encrypted before outsourcing. To preserve the confidentiality of the data, any computations performed by the server should only be on the encrypted data. In other words, the encrypted data should not be decrypted during any stage of the computation. This kind of task is commonly termed as query processing over encrypted data (QPED). One natural solution to solve the QPED problem is to utilize fully homomorphic encryption. However, fully homomorphic encryption is yet to be practical. The second solution is to adopt multi-server setting. However, the existing work is not efficient. Their implementations adopt costly primitives, such as secure comparison, binary decomposition among others, which reduce the efficiency of the whole protocols. Therefore, the improvement of these primitives results in high efficiency of the protocols. To have a well-defined scope, the following types of computations are considered: secure comparison (CMP), secure binary decomposition (SBD) and proxy re-encryption (PRE). We adopt the secret sharing scheme and paillier public key encryption as building blocks, and all computations can be done on the encrypted data by utilizing multiple servers. We analyze the security and the complexity of our proposed protocols, and their efficiencies are evaluated by comparing with the existing solutions.”--Abstract, page iii

On the Application of Identity-Based Cryptography in Grid Security

This thesis examines the application of identity-based cryptography (IBC) in designing security infrastructures for grid applications. In this thesis, we propose a fully identity-based key infrastructure for grid (IKIG). Our proposal exploits some interesting properties of hierarchical identity-based cryptography (HIBC) to replicate security services provided by the grid security infrastructure (GSI) in the Globus Toolkit. The GSI is based on public key infrastructure (PKI) that supports standard X.509 certificates and proxy certificates. Since our proposal is certificate-free and has small key sizes, it offers a more lightweight approach to key management than the GSI. We also develop a one-pass delegation protocol that makes use of HIBC properties. This combination of lightweight key management and efficient delegation protocol has better scalability than the existing PKI-based approach to grid security. Despite the advantages that IKIG offers, key escrow remains an issue which may not be desirable for certain grid applications. Therefore, we present an alternative identity-based approach called dynamic key infrastructure for grid (DKIG). Our DKIG proposal combines both identity-based techniques and the conventional PKI approach. In this hybrid setting, each user publishes a fixed parameter set through a standard X.509 certificate. Although X.509 certificates are involved in DKIG, it is still more lightweight than the GSI as it enables the derivation of both long-term and proxy credentials on-the-fly based only on a fixed certificate. We also revisit the notion of secret public keys which was originally used as a cryptographic technique for designing secure password-based authenticated key establishment protocols. We introduce new password-based protocols using identity-based secret public keys. Our identity-based techniques can be integrated naturally with the standard TLS handshake protocol. We then discuss how this TLS-like identity-based secret public key protocol can be applied to securing interactions between users and credential storage systems, such as MyProxy, within grid environments

CONSTRUCTION OF EFFICIENT AUTHENTICATION SCHEMES USING TRAPDOOR HASH FUNCTIONS

In large-scale distributed systems, where adversarial attacks can have widespread impact, authentication provides protection from threats involving impersonation of entities and tampering of data. Practical solutions to authentication problems in distributed systems must meet specific constraints of the target system, and provide a reasonable balance between security and cost. The goal of this dissertation is to address the problem of building practical and efficient authentication mechanisms to secure distributed applications. This dissertation presents techniques to construct efficient digital signature schemes using trapdoor hash functions for various distributed applications. Trapdoor hash functions are collision-resistant hash functions associated with a secret trapdoor key that allows the key-holder to find collisions between hashes of different messages. The main contributions of this dissertation are as follows: 1. A common problem with conventional trapdoor hash functions is that revealing a collision producing message pair allows an entity to compute additional collisions without knowledge of the trapdoor key. To overcome this problem, we design an efficient trapdoor hash function that prevents all entities except the trapdoor key-holder from computing collisions regardless of whether collision producing message pairs are revealed by the key-holder. 2. We design a technique to construct efficient proxy signatures using trapdoor hash functions to authenticate and authorize agents acting on behalf of users in agent-based computing systems. Our technique provides agent authentication, assurance of agreement between delegator and agent, security without relying on secure communication channels and control over an agent’s capabilities. 3. We develop a trapdoor hash-based signature amortization technique for authenticating real-time, delay-sensitive streams. Our technique provides independent verifiability of blocks comprising a stream, minimizes sender-side and receiver-side delays, minimizes communication overhead, and avoids transmission of redundant information. 4. We demonstrate the practical efficacy of our trapdoor hash-based techniques for signature amortization and proxy signature construction by presenting discrete log-based instantiations of the generic techniques that are efficient to compute, and produce short signatures. Our detailed performance analyses demonstrate that the proposed schemes outperform existing schemes in computation cost and signature size. We also present proofs for security of the proposed discrete-log based instantiations against forgery attacks under the discrete-log assumption

Contributions to the security and privacy of electronic ticketing systems

Un bitllet electrònic és un contracte en format digital entre dues parts, l'usuari i el proveïdor de serveis, on hi queda reflectit l'acord entre ambdós per tal que l'usuari rebi el servei que desitja per part del proveïdor. Els bitllets són emprats en diferents tipus de serveis, com esdeveniments lúdics o esportius, i especialment en l'àmbit del transport. En aquest cas permet reduir costos donat l'alt volum d'usuaris, a més de facilitar la identificació del flux de viatges. Aquesta informació permet preveure i planificar els sistemes de transport de forma més dinàmica. La seguretat dels bitllets electrònics és clau perquè es despleguin a l'entorn real, com també ho és la privadesa dels seus usuaris. La privadesa inclou tant l'anonimitat dels usuaris, és a dir, una acció no s'ha de poder atribuir fàcilment a un determinat usuari, com també la no enllaçabilitat dels diferents moviments d'un determinat usuari. En aquesta tesi proposem protocols de bitllets electrònics que mantinguin les propietats dels bitllets en paper juntament amb els avantatges dels bitllets digitals. Primerament fem un estat de l'art amb les propostes relacionades, analitzant-ne els requisits de seguretat que compleixen. Presentem un protocol de bitllets electrònics que incorpora els nous requisits de seguretat d'exculpabilitat i reutilització, diferents dels que haviem analitzat, tot complint també la privadesa pels usuaris. Posteriorment, presentem una proposta de bitllets electrònics adaptada als sistemes de pagament depenent de l'ús, bàsicament enfocat al transport, que incorpora tant l'anonimat pels usuaris, com també la enllaçabilitat a curt termini, és a dir, complint la no enllaçabilitat dels diferents moviments del mateix usuari, però permetent la enllaçabilitat de les accions relacionades amb el mateix trajecte (p.ex. entrada i sortida). Finalment, mitjançant una evolució de la mateixa tècnica criptogràfica utilitzada en el sistema de pagament per ús, millorant-ne el temps de verificació per a múltiples bitllets alhora (verificació en ``batch''), presentem una proposta que pot ser útil per a varis sistemes de verificació massiva de missatges, posant com a cas d'ús l'aplicació a sistemes de xarxes vehiculars.An electronic ticket is a digital contract between two parties, that is, the user and the service provider. An agreement between them is established in order that the user can receive the desired service. These tickets are used in different types of services, such as sports or entertainment events, especially in the field of transport. In the case of transport, costs can be reduced due to the high volume of users, and the identification of the travel flow is facilitated. This information allows the forecast and planification of transport systems more dynamically. The security of electronic tickets is very important to be deployed in the real scenarios, as well as the privacy for their users. Privacy includes both the anonymity of users, which implies that an action cannot be easily attributed to a particular user, and also the unlinkability of the different movements of that user. This thesis presents protocols which keep the same security requirements of paper tickets while offering the advantages of digital tickets. Firstly, we perform a state of the art with the related proposals, by analysing the security requirements considered. We then present an electronic ticketing system that includes the security requirements of exculpability and reusability, thus guaranteeing the privacy for users. We later present a proposal of electronic ticketing systems adapted to use-dependant payment systems, especially focused on transport, which includes both the anonymity of users and the short-term linkability of their movements. The related actions of a journey of a determined user can be linkable between them (i.e. entrance and exit of the system) but not with other movements that the user performs. Finally, as an extension of the previous use-dependant payment system solution, we introduce the case of mass-verification systems, where many messages have to be verified in short time, and we present a proposal as a vehicular network use case that guarantees privacy for users with short-term linkability and can verify these messages efficiently