A BSP algorithm for on-the-fly checking CTL* formulas on security protocols

International audienceThis paper presents a distributed (Bulk-Synchronous Parallel or bsp) algorithm to compute on-the-fly whether a structured model of a security protocol satisfies a ctl {Mathematical expression} formula. Using the structured nature of the security protocols allows us to design a simple method to distribute the state space under consideration in a need-driven fashion. Based on this distribution of the states, the algorithm for logical checking of a ltl formula can be simplified and optimised allowing, with few tricky modifications, the design of an efficient algorithm for ctl {Mathematical expression} checking. Some prototype implementations have been developed, allowing to run benchmarks to investigate the parallel behaviour of our algorithms

A second generation of nonrepudiation protocols

A non-repudiation protocol from party S to party R performs two tasks. First, the protocol enables party S to send to party R some text x along with sufficient evidence (that can convince a judge) that x was indeed sent by S. Second, the protocol enables party R to receive text x from S and to send to S sufficient evidence (that can convince a judge) that x was indeed received by R. The first generation of non-repudiation protocols were published in the period 1996-2000. In this dissertation, we design a second generation of non-repudiation protocols that enjoy several interesting properties. First, we identify in this dissertation a special class of non-repudiation protocols, called two-phase protocols. The two parties, S and R, in each two-phase protocol execute the protocol as specified until one of the two parties receives its needed proof. Then and only then does this party refrain from sending any more message specified by the protocol because these messages only help the other party complete its proof. We show that the execution of each two-phase protocol is deterministic and does not require synchronized real-time clocks. We also show that each two-phase protocol needs to involve a trusted third party T beside the two original parties, S and R. Second, we show that if party R in a two-phase protocol has a real-time clock and knows an upper bound on the round trip delay from R to S and back to R, then the two-phase protocol does not need to involve a trusted third party T. Third, we design a non-repudiation protocol for transferring file F from a sender S to a receiver R over a cloud C. This protocol is designed such that there is no direct communication between parties S and R. Rather all communications between S and R are carried out through cloud C. In this protocol parties S and R do not need to store a local copy of file F and the proofs that are needed by the two parties S and R (the only copy of file F and the proofs is stored in cloud C). Fourth, we design a new non-repudiation protocol from S to R over C where some of the proofs stored in cloud C get lost. This new protocol has an interesting stabilization property which ensures that when some of the proofs get lost, and one party can get the needed proofs but the other party cannot get its needed proofs from cloud C, then eventually, neither party is able to receive its needed proofs from cloud C. Fifth, we design a non-repudiation protocol for transferring files from a sender S to a subset of potential receivers {R.1, R.2, ..., R.n} over a cloud C. The protocol guarantees that after each file F is transferred from sender S to a subset of the potential receivers, then (1) each receiver R.i in the subset ends up with a proof that file F was indeed sent by sender S to R.i, and (2) sender S ends up with a proof that file F was indeed received from S by each receiver R.i in the subset.Computer Science

Towards Lightweight Secure User-Transparent And Privacy-Preserving Web Metering

Privacy is an issue today as more people are actively connecting and participating in the Internet. Problems arise when such concerning issue is coupled with security requirements of online applications. The web metering problem is the problem of counting the number of visits done by users to a webserver, additionally capturing data about these visits. There are trade-o s between designing secure web metering solutions and preserving users' privacy. There is also a dilemma between privacy preserving solutions versus accuracy of results. The problem becomes more difficult when the main interacting party, the user, is not inherently interested to participate and operations need to be carried out transparently. This thesis addresses the web metering problem in a hostile environment and proposes different web metering solutions. The web metering solutions operate in an environment where webservers or attackers are capable of invading users' privacy or modifying the web metering result. Threats in such environment are identified, using a well established threat model with certain assumptions, which are then used to derive privacy, security and functional requirements. Those requirements are used to show shortcomings in previous web metering schemes, which are then addressed by our proposed solutions. The central theme of this thesis is user's privacy by user-transparent solutions. Preserving users' privacy and designing secure web metering solutions that operate transparently to the user are two main goals of this research. Achieving the two goals can conflict with other requirements and such exploration was missed by former solutions in the literature. Privacy issues in this problem are the result of the dilemma of convincing interested parties of web metering results with sufficient details and non-repudiation evidence that can still preserve users' privacy. Relevant privacy guidelines are used to discuss and analyse privacy concerns in the context of the problem and consequently privacy-preserving solutions are proposed. Also, improving the usability through \securely" redesigning already used solutions will help into wider acceptance and universal deployment of the new solutions. Consequently, secure and privacy-preserving web metering solutions are proposed that operate transparently to the visitor. This thesis describes existing web metering solutions and analyses them with respect to different requirements and desiderata. It also describes and analyses new solutions which use existing security and authentication protocols, hardware devices and analytic codes. The proposed solutions provide a reasonable trade-o among privacy, security, accuracy and transparency. The first proposed solution, transparently to the user, reuses Identity Management Systems and hash functions for web metering purposes. The second hardware-based solution securely and transparently uses hardware devices and existing protocols in a privacy-preserving manner. The third proposed solution transparently collects different "unique" users' data and analyses fingerprints using privacy-preserving codes

Opening A Pandora's Box: Things You Should Know in the Era of Custom GPTs

The emergence of large language models (LLMs) has significantly accelerated the development of a wide range of applications across various fields. There is a growing trend in the construction of specialized platforms based on LLMs, such as the newly introduced custom GPTs by OpenAI. While custom GPTs provide various functionalities like web browsing and code execution, they also introduce significant security threats. In this paper, we conduct a comprehensive analysis of the security and privacy issues arising from the custom GPT platform. Our systematic examination categorizes potential attack scenarios into three threat models based on the role of the malicious actor, and identifies critical data exchange channels in custom GPTs. Utilizing the STRIDE threat modeling framework, we identify 26 potential attack vectors, with 19 being partially or fully validated in real-world settings. Our findings emphasize the urgent need for robust security and privacy measures in the custom GPT ecosystem, especially in light of the forthcoming launch of the official GPT store by OpenAI

Keeping Fairness Alive : Design and formal verification of optimistic fair exchange protocols

Fokkink, W.J. [Promotor]Pol, J.C. van de [Promotor

Research on security and privacy in vehicular ad hoc networks

Los sistemas de redes ad hoc vehiculares (VANET) tienen como objetivo proporcionar una plataforma para diversas aplicaciones que pueden mejorar la seguridad vial, la eficiencia del tráfico, la asistencia a la conducción, la regulación del transporte, etc. o que pueden proveer de una mejor información y entretenimiento a los usuarios de los vehículos. Actualmente se está llevando a cabo un gran esfuerzo industrial y de investigación para desarrollar un mercado que se estima alcance en un futuro varios miles de millones de euros. Mientras que los enormes beneficios que se esperan de las comunicaciones vehiculares y el gran número de vehículos son los puntos fuertes de las VANET, su principal debilidad es la vulnerabilidad a los ataques contra la seguridad y la privacidad.En esta tesis proponemos cuatro protocolos para conseguir comunicaciones seguras entre vehículos. En nuestra primera propuesta empleamos a todas las unidades en carretera (RSU) para mantener y gestionar un grupo en tiempo real dentro de su rango de comunicación. Los vehículos que entren al grupo de forma anónima pueden emitir mensajes vehículo a vehículo (V2V) que inmediatamente pueden ser verificados por los vehículos del mismo grupo (y grupos de vecinos). Sin embargo, en la primera fase del despliegue de este sistema las RSU pueden no estar bien distribuídas. Consecuentemente, se propone un conjunto de mecanismos para hacer frente a la seguridad, privacidad y los requisitos de gestión de una VANET a gran escala sin la suposición de que las RSU estén densamente distribuidas. La tercera propuesta se centra principalmente en la compresión de las evidencias criptográficas que nos permitirán demostrar, por ejemplo, quien era el culpable en caso de accidente. Por último, investigamos los requisitos de seguridad de los sistemas basados en localización (LBS) sobre VANETs y proponemos un nuevo esquema para la preservación de la privacidad de la localización en estos sistemas sobre dichas redes.Vehicular ad hoc network (VANET) systems aim at providing a platform for various applications that can improve traffic safety and efficiency, driver assistance, transportation regulation, infotainment, etc. There is substantial research and industrial effort to develop this market. It is estimated that the market for vehicular communications will reach several billion euros. While the tremendous benefits expected from vehicular communications and the huge number of vehicles are strong points of VANETs, their weakness is vulnerability to attacks against security and privacy.In this thesis, we propose four protocols for secure vehicle communications. In our first proposal, we employ each road-side unit (RSU) to maintain and manage an on-the-fly group within its communication range. Vehicles entering the group can anonymously broadcast vehicle-to-vehicle (V2V) messages, which can be instantly verified by the vehicles in the same group (and neighbor groups). However, at the early stage of VANET deployment, the RSUs may not be well distributed. We then propose a set of mechanisms to address the security, privacy, and management requirements of a large-scale VANET without the assumption of densely distributed RSUs. The third proposal is mainly focused on compressing cryptographic witnesses in VANETs. Finally, we investigate the security requirements of LBS in VANETs and propose a new privacy-preserving LBS scheme for those networks

Synthesising end-to-end security schemes through endorsement intermediaries

Composing secure interaction protocols dynamically for e-commerce continue to pose a number of challenges, such as lack of standard notations for expressing requirements and the difficulty involved in enforcing them. Furthermore, interaction with unknown entities may require finding common trusted intermediaries. Securing messages sent through such intermediaries require schemes that provide end-to-end security guarantees. In the past, e-commerce protocols such as SET were created to provide such end-to-end guarantees. However, such complex hand crafted protocols proved difficult to model check. This thesis addresses the end-to-end problems in an open dynamic setting where trust relationships evolve, and requirements of interacting entities change over time. Before interaction protocols can be synthesised, a number of research questions must be addressed. Firstly, to meet end-to-end security requirements, the security level along the message path must be made to reflect the requirements. Secondly, the type of endorsement intermediaries must reflect the message category. Thirdly, intermediaries must be made liable for their endorsements. This thesis proposes a number of solutions to address the research problems. End-to-end security requirements were arrived by aggregating security requirements of all interacting parties. These requirements were enforced by interleaving and composing basic schemes derived from challenge-response mechanisms. The institutional trust promoting mechanism devised allowed all vital data to be endorsed by authorised category specific intermediaries. Intermediaries were made accountable for their endorsements by being required to discharge or transfer proof obligations placed on them. The techniques devised for aggregating and enforcing security requirements allow dynamic creation of end-to-end security schemes. The novel interleaving technique devised allows creation of provably secure multiparty schemes for any number of recipients. The structured technique combining compositional approach with appropriate invariants and preconditions makes model checking of synthesised schemes unnecessary. The proposed framework combining endorsement trust with schemes making intermediaries accountable provides a way to alleviate distrust between previously unknown e-commerce entities