A Mediated Definite Delegation Model allowing for Certified Grid Job Submission

Grid computing infrastructures need to provide traceability and accounting of their users" activity and protection against misuse and privilege escalation. A central aspect of multi-user Grid job environments is the necessary delegation of privileges in the course of a job submission. With respect to these generic requirements this document describes an improved handling of multi-user Grid jobs in the ALICE ("A Large Ion Collider Experiment") Grid Services. A security analysis of the ALICE Grid job model is presented with derived security objectives, followed by a discussion of existing approaches of unrestricted delegation based on X.509 proxy certificates and the Grid middleware gLExec. Unrestricted delegation has severe security consequences and limitations, most importantly allowing for identity theft and forgery of delegated assignments. These limitations are discussed and formulated, both in general and with respect to an adoption in line with multi-user Grid jobs. Based on the architecture of the ALICE Grid Services, a new general model of mediated definite delegation is developed and formulated, allowing a broker to assign context-sensitive user privileges to agents. The model provides strong accountability and long- term traceability. A prototype implementation allowing for certified Grid jobs is presented including a potential interaction with gLExec. The achieved improvements regarding system security, malicious job exploitation, identity protection, and accountability are emphasized, followed by a discussion of non- repudiation in the face of malicious Grid jobs

Oracular Byzantine Reliable Broadcast

Byzantine Reliable Broadcast (BRB) is a fundamental distributed computing primitive, with applications ranging from notifications to asynchronous payment systems. Motivated by practical consideration, we study Client-Server Byzantine Reliable Broadcast (CSB), a multi-shot variant of BRB whose interface is split between broadcasting clients and delivering servers. We present Draft, an optimally resilient implementation of CSB. Like most implementations of BRB, Draft guarantees both liveness and safety in an asynchronous environment. Under good conditions, however, Draft achieves unparalleled efficiency. In a moment of synchrony, free from Byzantine misbehaviour, and at the limit of infinitely many broadcasting clients, a Draft server delivers a b-bits payload at an asymptotic amortized cost of 0 signature verifications, and (log?(c) + b) bits exchanged, where c is the number of clients in the system. This is the information-theoretical minimum number of bits required to convey the payload (b bits, assuming it is compressed), along with an identifier for its sender (log?(c) bits, necessary to enumerate any set of c elements, and optimal if broadcasting frequencies are uniform or unknown). These two achievements have profound practical implications. Real-world BRB implementations are often bottlenecked either by expensive signature verifications, or by communication overhead. For Draft, instead, the network is the limit: a server can deliver payloads as quickly as it would receive them from an infallible oracle

An effective, secure and efficient tagging method for integrity protection of outsourced data in a public cloud storage

Data Integrity Auditing (DIA) is a security service for checking the integrity of data stored in a PCS (Public Cloud Storage), a third-party based storage service. A DIA service is provided by using integrity tags (hereafter referred to tags). This paper proposes a novel tagging method, called Tagging of Outsourced Data (TOD), for generating and verifying tags of files. TOD has a number of unique properties: (i) it supports both public and private verifiability, and achieves this property with a low level of overhead at the user end, making it particularly attractive to mobile users with resource-constrained devices, (ii) it protects data confidentiality, supports dynamic tags and is resilient against tag forgery and tag tampering (i.e. by authorised insiders) at the same time in more secure and efficient, making the method more suited to the PCS environment, (iii) it supports tags deduplication, making it more efficient, particularly for the user who has many files with data redundancy. Comprehensive security analysis and performance evaluation have been conducted to demonstrate the efficacy and efficiency of the approach taken in the design

Practical Certificateless Aggregate Signatures From Bilinear Maps

Aggregate signature is a digital signature with a striking property that anyone can aggregate n individual signatures on n different messages which are signed by n distinct signers, into a single compact signature to reduce computational and storage costs. In this work, two practical certificateless aggregate signature schemes are proposed from bilinear maps. The first scheme CAS-1 reduces the costs of communication and signer-side computation but trades off the storage, while CAS-2 minimizes the storage but sacrifices the communication costs. One can choose either of the schemes by consideration of the application requirement. Compare with ID-based schemes, our schemes do not entail public key certificates as well and achieve the trust level 3, which imply the frauds of the authority are detectable. Both of the schemes are proven secure in the random oracle model by assuming the intractability of the computational Diffie-Hellman problem over the groups with bilinear maps, where the forking lemma technique is avoided

An Extensible Framework for Implementing and Validating Byzantine Fault-tolerant Protocols

HotStuff is a Byzantine fault-tolerant state machine replication protocol that incurs linear communication costs to achieve consensus. This linear scalability promoted the protocol to be adopted as the consensus mechanism in permissioned blockchains. This paper discusses the architecture, testing, and evaluation of our extensible framework to implement HotStuff and its variants. The framework already contains three HotStuff variants and other interchangeable components for cryptographic operations and leader selection. Inspired by the Twins approach, we also provide a testing framework for validating protocol implementations by inducing Byzantine behaviors. Test generation is protocol-agnostic; new protocols can execute the test suite with little-to-no modifications. We report relevant insights on how we benefited from Twins for validation and test-driven development. Leveraging our deployment tool, we evaluated our implementation in various configurations.acceptedVersio

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