Generalized Ring Signatures

Abstract-The concept of ring signature was first introduced b

Security and privacy issues in some special-puropse networks

This thesis is about providing security and privacy to new emergent applications which are based on special-purpose networks. More precisely, we study different aspects regarding security and privacy issues related to sensor networks, mobile ad hoc networks, vehicular ad hoc networks and social networks.Sensor networks consist of resource-constrained wireless devices with sensor capabilities. This emerging technology has a wide variety of applications related to event surveillance like emergency response, habitat monitoring or defense-related networks.Ad hoc networks are suited for use in situations where deploying an infrastructure is not cost effective or is not possible for any other reason. When the nodes of an ad hoc network are small mobile devices (e.g. cell phones or PDAs), such a network is called mobile ad hoc network. One of many possible uses of MANETs is to provide crisis management services applications, such as in disaster recovery, where the entire communication infrastructure is destroyed and reestablishing communication quickly is crucial. Another useful situation for MANETs is a scenario without fixed communication systems where there is the need for any kind of collaborative computing. Such situation can occur in both business and military environments.When the mobile nodes of a MANET are embedded in cars, such a network is called Vehicular Ad hoc Network (VANET). This kind of networks can be very useful to increase the road traffic safety and they will be deployed for real use in the forthcoming years. As a proof of that, eight important European vehicle manufacturers have founded the CAR 2 CAR Communication Consortium. This non-profit organisation is dedicated to the objective of further increasing traffic safety and efficiency by means of inter-vehicle communications.Social networks differ from the special-purpose networks commented above in that they are not physical networks. Social networks are applications that work through classic networks. They can be defined as a community of web users where each user can publish and share information and services. Social networks have become an object of study both in computer and social sciences, with even dedicated journals and conferences.The special-purpose networks described above provide a wide range of new services and applications. Even though they are expected to improve the society in several ways, these innovative networks and their related applications bring also security and privacy issues that must be addressed.This thesis solves some security and privacy issues related to such new applications and services. More specifically, it focuses on:·Secure information transmission in many-to-one scenarios with resource-constrained devices such as sensor networks.·Secure and private information sharing in MANETs.·Secure and private information spread in VANETs.·Private resource access in social networks.Results presented in this thesis include four contributions published in ISI JCR journals (IEEE Transactions on Vehicular Technology, Computer Networks (2) and Computer Communications) and two contributions published in two international conferences (Lecture Notes in Computer Science).Esta tesis trata diversos problemas de seguridad y privacidad que surgen al implantar en escenarios reales novedosas aplicaciones basadas en nuevos y emergentes modelos de red. Estos nuevos modelos de red difieren significativamente de las redes de computadores clásicas y son catalogadas como redes de propósito especial. Específicamente, en este trabajo se estudian diferentes aspectos relacionados con la seguridad de la información y la privacidad de los usuarios en redes de sensores, redes ad hoc móviles (MANETs), redes ad hoc vehiculares (VANETs) y redes sociales.Las redes de sensores están formadas por dispositivos inalámbricos muy limitados a nivel de recursos (capacidad de computación y batería) que detectan eventos o condiciones del entorno donde se instalan. Esta tecnología tiene una amplia variedad de aplicaciones entre las que destacan la detección de emergencias o la creación de perímetros de seguridad. Una MANET esta formada por nodos móviles conectados entre ellos mediante conexiones inalámbricas y de forma auto-organizada. Este tipo de redes se constituye sin la ayuda de infraestructuras, por ello son especialmente útiles en situaciones donde implantar una infraestructura es inviable por ser su coste demasiado elevado o por cualquier otra razón. Una de las muchas aplicaciones de las MANETs es proporcionar servicio en situaciones críticas (por ejemplo desastres naturales) donde la infraestructura de comunicaciones ha sido destruida y proporcionar conectividad rápidamente es crucial. Otra aplicación directa aparece en escenarios sin sistemas de comunicación fijos donde existe la necesidad de realizar algún tipo de computación colaborativa entre diversas máquinas. Esta situación se da tanto en ámbitos empresariales como militares.Cuando los nodos móviles de una MANET se asocian a vehículos (coches, camiones.), dicha red se denomina red ad hoc vehicular o VANET. Este tipo de redes pueden ser muy útiles para incrementar la seguridad vial y se espera su implantación para uso real en los próximos años. Como prueba de la gran importancia que tiene esta tecnología, los ocho fabricantes europeos más importantes han fundado la CAR 2 CAR Communication Consortium. Esta organización tiene como objetivo incrementar la seguridad y la eficiencia del tráfico mediante el uso de comunicaciones entre los vehículos.Las redes sociales se diferencian de las redes especiales descritas anteriormente en que éstas no son redes físicas. Las redes sociales son aplicaciones que funcionan a través de las redes de computadores clásicas. Una red de este tipo puede ser definida como una comunidad de usuarios web en donde dichos usuarios pueden publicar y compartir información y servicios. En la actualidad, las redes sociales han adquirido gran importancia ofreciendo un amplio abanico de posibilidades a sus usuarios: trabajar de forma colaborativa, compartir ficheros, búsqueda de nuevos amigos, etc.A continuación se resumen las aplicaciones en las que esta tesis se centra según el tipo de red asociada:·Transmisión segura de información en escenarios muchos-a-uno (múltiples emisores y un solo receptor) donde los dispositivos en uso poseen recursos muy limitados. Este escenario es el habitual en redes de sensores.·Distribución de información de forma segura y preservando la privacidad de los usuarios en redes ad hoc móviles.·Difusión de información (con el objeto de incrementar la seguridad vial) fidedigna preservando la privacidad de los usuarios en redes ad hoc vehiculares.·Acceso a recursos en redes sociales preservando la privacidad de los usuarios. Los resultados de la tesis incluyen cuatro publicaciones en revistas ISI JCR (IEEE Transactions on Vehicular Technology, Computer Networks (2) y Computer Communications) y dos publicaciones en congresos internacionales(Lecture Notes in Computer Science)

Society-oriented cryptographic techniques for information protection

Groups play an important role in our modern world. They are more reliable and more trustworthy than individuals. This is the reason why, in an organisation, crucial decisions are left to a group of people rather than to an individual. Cryptography supports group activity by offering a wide range of cryptographic operations which can only be successfully executed if a well-defined group of people agrees to co-operate. This thesis looks at two fundamental cryptographic tools that are useful for the management of secret information. The first part looks in detail at secret sharing schemes. The second part focuses on society-oriented cryptographic systems, which are the application of secret sharing schemes in cryptography. The outline of thesis is as follows

XML security in XML data integrity, authentication, and confidentiality

The widely application of XML has increasingly required high security. XML security confronts some challenges that are strong relating to its features. XML data integrity needs to protect element location information and contextreferential meaning as well as data content integrity under fine-grained security situations. XML data authentication must satisfy a signing process under a dependent and independent multi-signature generation scenario. When several different sections are encrypted within the XML data, it cannot query the encrypted contents without decrypting the encrypted portions. The technologies relating to XML security demand further development. This thesis aims to improve XML security relative technologies, and make them more practicable and secure. A novel revocation information validation approach for X.509 certificate is proposed based on the XML digital signature technology. This approach reduces the complexity of XKMS or PKI systems because it eliminates the requirement for additional revocation checking from XKMS or CA. The communication burden between server and client could be alleviated. The thesis presents the context-referential integrity for XML data. An integrity solution for XML data is also proposed based on the concatenated hash function. The integrity model proposed not only ensures XML data content integrity, but also protects the structure integrity and elements’ context relationship within an XML data. If this model is integrated into XML signature technology, the signature cannot be copied to another document still keeping valid. A new series-parallel XML multi-signature scheme is proposed. The presented scheme is a mixed order specified XML multi-signature scheme according to a dependent and independent signing process. Using presented XML data integrity-checking pool to provide integrity-checking for decomposed XML data, it makes signing XPath expression practicable, rather than signing XML data itself. A new labeling scheme for encrypted XML data is presented to improve the efficiency of index information maintenance which is applied to support encrypted XML data query processing. The proposed labelling scheme makes maintenance index information more efficient, and it is easy to update XML data with decreasing the number of affected nodes to the lowest. In order to protect structural information for encrypted XML data, the encrypted nodes are removed from original XML data, and structural information is hidden. A case study is carried out to demonstrate how the proposed XML security relative approaches and schemes can be applied to satisfy fine-grained XML security in calibration certificate management.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Identity-based threshold group signature scheme based on multiple hard number theoretic problems

We introduce in this paper a new identity-based threshold signature (IBTHS) technique, which is based on a pair of intractable problems, residuosity and discrete logarithm. This technique relies on two difficult problems and offers an improved level of security relative to an individual hard problem. The majority of the denoted IBTHS techniques are established on an individual difficult problem. Despite the fact that these methods are secure, however, a prospective solution of this sole problem by an adversary will enable him/her to recover the entire private data together with secret keys and configuration values of the associated scheme. Our technique is immune to the four most familiar attack types in relation to the signature schemes. Enhanced performance of our proposed technique is verified in terms of minimum cost of computations required by both of the signing algorithm and the verifying algorithm in addition to immunity to attacks

Security Pitfalls of a Provably Secure Identity-based Multi-Proxy Signature Scheme

An identity-based multi-proxy signature is a type of proxy signatures in which the delegation of signing right is distributed among a number of proxy signers. In this type of cryptographic primitive, cooperation of all proxy signers in the proxy group generates the proxy signatures of roughly the same size as that of standard proxy signatures on behalf of the original signer, which is more efficient than transmitting individual proxy signatures. Since identity-based multi-proxy signatures are useful in distributed systems, grid computing, presenting a provably secure identity-based multi-proxy scheme is desired. In 2013, Sahu and Padhye proposed the first provably secure identity-based multi-proxy signature scheme in the random oracle model, and proved that their scheme is existential unforgeable against adaptive chosen message and identity attack. Unfortunately, in this paper, we show that their scheme is insecure. We present two forgery attacks on their scheme. Furthermore, their scheme is not resistant against proxy key exposure attack. As a consequence, there is no provably secure identity-based multi-proxy signature scheme secure against proxy key exposure attack to date