@article {Roman2023a, title = {Current Perspectives on Securing Critical Infrastructures{\textquoteright} Supply Chains}, journal = {IEEE Security \& Privacy}, year = {In Press}, publisher = {IEEE}, issn = {1540-7993}, author = {Rodrigo Roman and Cristina Alcaraz and Javier Lopez and Kouichi Sakurai} } @inproceedings {Alcaraz2022c, title = {Collaborative anomaly detection system for charging stations}, booktitle = {The 27th European Symposium on Research in Computer Security (ESORICS 2022)}, volume = {13555}, year = {2022}, month = {09/2022}, pages = {716{\textendash}736}, publisher = {Springer, Cham}, organization = {Springer, Cham}, abstract = {

In recent years, the deployment of charging infrastructures has been increasing exponentially due to the high energy demand of electric vehicles, forming complex charging networks. These networks pave the way for the emergence of new unknown threats in both the energy and transportation sectors. Economic damages and energy theft are the most frequent risks in these environments. Thus, this paper aims to present a solution capable of accurately detecting unforeseen events and possible fraud threats that arise during charging sessions at charging stations through the current capabilities of the Machine Learning (ML) algorithms. However, these algorithms have the drawback of not fitting well in large networks and generating a high number of false positives and negatives, mainly due to the mismatch with the distribution of data over time. For that reason, a Collaborative Anomaly Detection System for Charging Stations (here referred to as CADS4CS) is proposed as an optimization measure. CADS4CS has a central analysis unit that coordinates a group of independent anomaly detection systems to provide greater accuracy using a voting algorithm. In addition, CADS4CS has the feature of continuously retraining ML models in a collaborative manner to ensure that they are adjusted to the distribution of the data. To validate the approach, different use cases and practical studies are addressed to demonstrate the effectiveness and efficiency of the solution.

}, keywords = {Charging station, Collaborative anomaly detection, Machine Learning, Voting system}, doi = {https://doi.org/10.1007/978-3-031-17146-8_35}, author = {Jesus Cumplido and Cristina Alcaraz and Javier Lopez} } @article {alcaraz2019a, title = {Covert Channels-based Stealth Attacks in Industry 4.0}, journal = {IEEE Systems Journal.}, volume = {13}, year = {2019}, month = {12/2019}, pages = {3980-3988}, publisher = {IEEE}, abstract = {

Industry 4.0 advent opens several cyber-threats scenarios originally designed for classic information technology, drawing the attention to the serious risks for the modern industrial control networks.\ To cope with this problem, in this paper we address the security issues related to covert channels applied to industrial networks, identifying the new vulnerability points when information technologies converge with operational technologies such as edge computing infrastructures.\ Specifically, we define two signaling strategies where we exploit the Modbus/TCP protocol as target to set up a covert channel. Once the threat channel is established, passive and active offensive attacks (i.e. data exfiltration and command an control, respectively) are further exploited by implementing and testing them on a real Industrial Internet of Things testbed.\ The experimental results highlight the potential damage of such specific threats, and the easy extrapolation of the attacks to other types of channels in order to show the new risks for Industry 4.0. Related to this, we discuss some countermeasures to offer an overview of possible mitigation and defense measures.

}, issn = {1932-8184}, doi = {https://doi.org/10.1109/JSYST.2019.2912308}, url = {https://ieeexplore.ieee.org/document/8715420?source=authoralert}, author = {Cristina Alcaraz and Giuseppe Bernieri and Federica Pascucci and Javier Lopez and Roberto Setola} } @article {rub2019cose, title = {Current Cyber-Defense Trends in Industrial Control Systems}, journal = {Computers \& Security Journal}, volume = {87}, year = {2019}, month = {11/2019}, publisher = {Elsevier}, type = {SECRYPT 2017 Special Issue}, abstract = {

Advanced Persistent Threats (APTs) have become a serious hazard for any critical infrastructure, as a single solution to protect all industrial assets from these complex attacks does not exist. It is then essential to understand what are the defense mechanisms that can be used as a first line of defense. For this purpose, this article will firstly study the spectrum of attack vectors that APTs can use against existing and novel elements of an industrial ecosystem. Afterwards, this article will provide an analysis of the evolution and applicability of Intrusion Detection Systems (IDS) that have been proposed in both the industry and academia.

}, keywords = {APT, Industrial Control, Industry 4.0, Intrusion Detection, SCADA}, issn = {0167-4048}, doi = {https://doi.org/10.1016/j.cose.2019.06.015}, author = {Juan E. Rubio and Cristina Alcaraz and Rodrigo Roman and Javier Lopez} } @inproceedings {CRAT2018, title = {Capture the RAT: Proximity-based Attacks in 5G using the Routine Activity Theory}, booktitle = {The 16th IEEE International Conference on Dependable, Autonomic and Secure Computing (DASC 2018)}, year = {2018}, month = {08/2018}, pages = {520-527}, publisher = {IEEE}, organization = {IEEE}, address = {Athens, Greece}, abstract = {

The fifth generation of cellular networks (5G) will enable different use cases where security will be more critical than ever before (e.g. autonomous vehicles and critical IoT devices). Unfortunately, the new networks are being built on the certainty that security problems can not be solved in the short term. Far from reinventing the wheel, one of our goals is to allow security software developers to implement and test their reactive solutions for the capillary network of 5G devices. Therefore, in this paper a solution for analysing proximity-based attacks in 5G environments is modelled and tested using OMNET++. The solution, named CRAT, is able to decouple the security analysis from the hardware of the device with the aim to extend the analysis of proximity-based attacks to different use-cases in 5G. We follow a high-level approach, in which the devices can take the role of victim, offender and guardian following the principles of the routine activity theory.\ 

}, isbn = {978-1-5386-7518-2}, doi = {10.1109/DASC/PiCom/DataCom/CyberSciTec.2018.00100}, url = {https://ieeexplore.ieee.org/document/8511943}, author = {Ana Nieto and Antonio Acien and Javier Lopez} } @inproceedings {1701, title = {A comprehensive methodology for deploying IoT honeypots}, booktitle = {15th International Conference on Trust, Privacy and Security in Digital Business (TrustBus 2018)}, volume = {LNCS 11033}, year = {2018}, month = {09/2018}, pages = {229{\textendash}243}, publisher = {Springer Nature Switzerland AG}, organization = {Springer Nature Switzerland AG}, address = {Regensburg (Germany)}, abstract = {

Recent news have raised concern regarding the security on the IoT field. Vulnerabilities in devices are arising and honeypots are an excellent way to cope with this problem. In this work, current solutions for honeypots in the IoT context, and other solutions adaptable to it are analyzed in order to set the basis for a methodology that allows deployment of IoT honeypot.

}, keywords = {Honeypot, IoT, methodology, security}, doi = {https://doi.org/10.1007/978-3-319-98385-1_16}, author = {Antonio Acien and Ana Nieto and Gerardo Fernandez and Javier Lopez} } @article {cazorla2016cyber, title = {Cyber Stealth Attacks in Critical Information Infrastructures}, journal = {IEEE Systems Journal}, volume = {12}, year = {2018}, month = {06/2018}, pages = {1778-1792}, publisher = {IEEE}, abstract = {

Current Critical Infrastructures (CIs) are complex interconnected industrial systems that, in recent years, have incorporated information and communications technologies such as connection to the Internet and commercial off-the-shelf components. This makes them easier to operate and maintain, but exposes them to the threats and attacks that inundate conventional networks and systems. This paper contains a comprehensive study on the main stealth attacks that threaten CIs, with a special focus on Critical Information Infrastructures (CIIs). This type of attack is characterized by an adversary who is able to finely tune his actions to avoid detection while pursuing his objectives. To provide a complete analysis of the scope and potential dangers of stealth attacks we determine and analyze their stages and range, and we design a taxonomy to illustrate the threats to CIs, offering an overview of the applicable countermeasures against these attacks. From our analysis we understand that these types of attacks, due to the interdependent nature of CIs, pose a grave danger to critical systems where the threats can easily cascade down to the interconnected systems.\ 

}, keywords = {Control systems, Countermeasures, Critical Infrastructures, Detection and Protection, Stealth Attacks}, issn = {1932-8184}, doi = {10.1109/JSYST.2015.2487684}, url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=\&arnumber=7445136\&isnumber=8350419}, author = {Lorena Cazorla and Cristina Alcaraz and Javier Lopez} } @article {alcarazlopez-IEEESystems-2017, title = {A Cyber-Physical Systems-Based Checkpoint Model for Structural Controllability}, journal = {IEEE Systems Journal}, volume = {12}, year = {2018}, month = {12/2018}, pages = {3543-3554}, publisher = {IEEE}, abstract = {

The protection of critical user-centric applications,\ such as Smart Grids and their monitoring systems, has become\ one of the most cutting-edge research areas in recent years.\ The dynamic complexity of their cyber-physical systems (CPSs)\ and their strong inter-dependencies with power systems, are\ bringing about a significant increase in security problems that\ may be exploited by attackers. These security holes may, for\ example, trigger the disintegration of the structural controllability\ properties due to the problem of non-locality, affecting, sooner\ or later, the provision of the essential services to end-users.\ One way to address these situations could be through automatic\ checkpoints in charge of inspecting the healthy status of the\ control network and its critical nature. This inspection can be\ subject to special mechanisms\ composed of trustworthy cyberphysical\ elements\ capable of detecting structural changes in the\ control and activating restoration procedures\ with support for\ warning. This is precisely the aim of this paper, which presents\ a CPSs-based checkpoint model with the capacity to manage\ heterogeneous replications that help ensure data redundancy,\ thereby guaranteeing the validity of the checkpoints. As a support\ to this study,\ a theoretical and practical analysis is addressed to\ show the functionality of the approach in real contexts.

}, keywords = {Critical Control Systems, cyber-physical systems, Smart grids, structural controllability}, issn = {1932-8184}, doi = {https://doi.org/10.1109/JSYST.2017.2740719}, url = {http://ieeexplore.ieee.org/document/8057984/}, author = {Cristina Alcaraz and Javier Lopez} } @incollection {1590, title = {Cyber-Physical Systems for Wide-Area Situational Awareness}, booktitle = {Cyber-Physical Systems: Foundations, Principles and Applications}, number = {Intelligent Data-Centric Systems}, year = {2017}, month = {2017}, pages = {305 - 317}, publisher = {Academic Press}, organization = {Academic Press}, chapter = {20}, address = {Boston}, abstract = {

Abstract Cyber-physical systems (CPSs), integrated in critical infrastructures, could provide the minimal services that traditional situational awareness (SA) systems demand. However, their application in SA\ solutions for the protection of large control distributions against unforeseen faults may be insufficient. Dynamic protection measures have to be provided not only to locally detect unplanned deviations but also to prevent, respond, and restore from these deviations. The provision of these services as an integral part of the SA\ brings about a new research field known as wide-area situational awareness (WASA), highly dependent on CPSs\ for control from anywhere across multiple interconnections, and at any time. Thus, we review the state-of-the art of this new paradigm, exploring the different preventive and corrective measures considering the heterogeneity of CPSs, resulting in a guideline for the construction of automated WASA\ systems.

}, keywords = {Control systems, Critical Infrastructure Protection, cyber-physical systems, Detection, Response, restoration, Wide-Area Situational Awareness}, isbn = {978-0-12-803801-7}, doi = {http://dx.doi.org/10.1016/B978-0-12-803801-7.00020-1}, author = {Cristina Alcaraz and Lorena Cazorla and Javier Lopez} } @article {NL-COMCOM15, title = {Contextualising Heterogeneous Information in Unified Communications with Security Restrictions}, journal = {Computer Communications}, volume = {68}, year = {2015}, month = {09/2015}, pages = {33-46}, publisher = {Elsevier}, abstract = {

The lack of abstraction in a growing semantic, virtual and abstract world poses new challenges for assessing security and QoS tradeoffs. For example, in Future Internet scenarios, where Unified Communications (UC) will take place, being able to predict the final devices that will form the network is not always possible. Without this information the analysis of the security and QoS tradeoff can only be based on partial information to be completed when more information about the environment is available. In this paper, we extend the description of context-based parametric relationship model, providing a tool for assessing the security and QoS tradeoff (SQT) based on interchangeable contexts. Our approach is able to use the heterogeneous information produced by scenarios where UC is present.

}, keywords = {Context, QoS, security, Tradeoff}, issn = {0140-3664}, doi = {10.1016/j.comcom.2015.07.015}, url = {http://www.sciencedirect.com/science/article/pii/S0140366415002534}, author = {Ana Nieto and Javier Lopez} } @inproceedings {431, title = {A Context-based Parametric Relationship Model (CPRM) to Measure the Security and QoS tradeoff in Configurable Environments}, booktitle = {IEEE International Conference on Communications (ICC{\textquoteright}14)}, year = {2014}, month = {06/2014}, pages = {755-760}, publisher = {IEEE Communications Society}, organization = {IEEE Communications Society}, address = {Sydney (Australia)}, abstract = {

Heterogeneity of future networks requires the use of extensible models to understand the Security and QoS tradeoff. We believe that a good starting point is to analyze the Security and QoS tradeoff from a parametric point of view and, for this reason, in a previous paper, we defined the Parametric Rela- tionship Model (PRM) to define relationships between Security and QoS parameters. In this paper, we extend that approach in order to change the behaviour of the model so that different contexts in the same system are considered; that is, to provide a Context-based Parametric Relationship Model (CPRM). The final aim is to provide useful tools for system administrators in order to help them deal with Security and QoS tradeoff issues in the configuration of the environment.\ 

}, isbn = {978-1-4799-2003-7}, doi = {10.1109/ICC.2014.6883410}, author = {Ana Nieto and Javier Lopez} } @article {rios2013a, title = {Covert Communications through Network Configuration Messages}, journal = {Computers \& Security}, volume = {39, Part A}, year = {2013}, month = {Nov 2013}, pages = {34 - 46}, publisher = {Elsevier}, abstract = {

Covert channels are a form of hidden communication that may violate the integrity of systems. Since their birth in Multi-Level Security systems in the early 70{\textquoteright}s they have evolved considerably, such that new solutions have appeared for computer networks mainly due to vague protocols specifications. In this paper we concentrate on short-range covert channels and analyze the opportunities of concealing data in various extensively used protocols today. From this analysis we observe several features that can be effectively exploited for subliminal data transmission in the Dynamic Host Configuration Protocol (DHCP). The result is a proof-of-concept implementation, HIDE\_DHCP, which integrates three different covert channels each of which accommodate to different stealthiness and capacity requirements. Finally, we provide a theoretical and experimental analysis of this tool in terms of its reliability, capacity, and detectability.

}, keywords = {Covert channels, Information Warfare, Intrusion Detection, Network Security, System Information Security}, issn = {0167-4048}, doi = {10.1016/j.cose.2013.03.004}, author = {Ruben Rios and Jose A. Onieva and Javier Lopez} } @inproceedings {onieva2012, title = {Como proteger la privacidad de los usuarios en Internet. Verificaci{\'o}n an{\'o}nima de la mayor{\'\i}a de edad}, booktitle = {XII Reuni{\'o}n Espa{\~n}ola sobre Criptolog{\'\i}a y Seguridad de la Informaci{\'o}n - RECSI 2012}, year = {2012}, month = {Sep 2012}, pages = {297-302}, publisher = {Mondragon}, organization = {Mondragon}, address = {San Sebastian (Spain)}, isbn = {978-84-615-9933-2}, author = {Jose A. Onieva and Isaac Agudo and Javier Lopez and G. Drapper-Gil and M.F. Hinarejos} } @inproceedings {moyano2012trustbus, title = {A Conceptual Framework for Trust Models}, booktitle = {9th International Conference on Trust, Privacy \& Security in Digital Business (TrustBus 2012)}, series = {LNCS}, volume = {7449}, year = {2012}, month = {Sep 2012}, pages = {93-104}, publisher = {Springer Verlag}, organization = {Springer Verlag}, address = {Vienna}, abstract = {

During the last twenty years, a huge amount of trust and reputation models have been proposed, each of them with their own particularities and targeting different domains. While much effort has been made in defining ever-increasing complex models, little attention has been paid to abstract away the particularities of these models into a common set of easily understandable concepts. We propose a conceptual framework for computational trust models that will be used for analyzing their features and for comparing heterogeneous and relevant trust models.

}, isbn = {978-3-642-32286-0}, issn = {0302-9743}, doi = {10.1007/978-3-642-32287-7}, author = {Francisco Moyano and Carmen Fernandez-Gago and Javier Lopez}, editor = {Fischer-H{\"u}bner, Simone and Katsikas, Sokratis and Quirchmayr, Gerald} } @article {Roman2010, title = {A Cross-layer Approach for Integrating Security Mechanisms in Sensor Networks Architectures}, journal = {Wireless Communications and Mobile Computing}, volume = {11}, year = {2011}, pages = {267-276}, publisher = {Wiley}, abstract = {

The wireless sensor networks (WSN) paradigm is especially vulnerable against external and internal attacks. Therefore, it is necessary to develop security mechanisms and protocols to protect them. These mechanisms must become an integral part of the software architecture and network stack of a sensor node. A question that remains is how to achieve this integration. In this paper we check how both academic and industrial solutions tackle this issue, and we present the concept of a transversal layer, where all the different security mechanisms could be contained. This way, all the elements of the architecture can interact with the security mechanisms, and the security mechanisms can have a holistic point of view of the whole architecture. We discuss the advantages of this approach, and also present how the transversal layer concept was applied to a real middleware architecture.

}, keywords = {architecture, cross-layer, middleware, security, Sensor Networks}, issn = {1530-8669}, doi = {10.1002/wcm.1006}, url = {http://dx.doi.org/10.1002/wcm.1006}, author = {Rodrigo Roman and Javier Lopez and Pablo Najera} } @article {FerrerGomilla2009, title = {Certified electronic mail: Properties revisited}, journal = {Computers \& Security}, volume = {29}, number = {2}, year = {2010}, pages = {167 - 179}, abstract = {

Certified electronic mail is an added value to traditional electronic mail. In the definition of this service some differences arise: a message in exchange for a reception proof, a message and a non repudiation of origin token in exchange for a reception proof, etc. It greatly depends on whether we want to emulate the courier service or improve the service in the electronic world. If the definition of the service seems conflictive, the definition of the properties and requirements of a good certified electronic mail protocol is even more difficult. The more consensuated features are the need of a fair exchange and the existence of a trusted third party (TTP). Each author chooses the properties that considers the most important, and many times the list is conditioned by the proposal. Which kind of TTP must be used? Must it be verifiable, transparent and/or stateless? Which features must the communication channel fulfil? Which temporal requirements must be established? What kind of fairness is desired? What efficiency level is required? Are confidentiality or transferability of the proofs compulsory properties? In this paper we collect the definitions, properties and requirements related with certified electronic mail. The aim of the paper is to create a clearer situation and analyze how some properties cannot be achieved simultaneously. Each protocol designer will have to decide which properties are the most important in the environment in where the service is to be deployed.

}, keywords = {Certified electronic mail, Fairness, Non repudiation, Properties, Timeliness, Trusted third parties}, issn = {0167-4048}, doi = {DOI: 10.1016/j.cose.2009.06.009}, url = {http://www.sciencedirect.com/science/article/B6V8G-4WR19XR-1/2/eda89f747b077fc68fa061f213ddf6d5}, author = {Josep L. Ferrer-Gomilla and Jose A. Onieva and Magdalena Payeras and Javier Lopez} } @inproceedings {JoseA.Montenegro2010, title = {Computacion Segura Multiparte Aplicada a Subastas Electr{\'o}nicas}, booktitle = {IX Jornadas de Ingenier{\'\i}a Telemenatica (JITEL 2010)}, year = {2010}, month = {Octubre}, abstract = {

La confidencialidad ha pasado de ser un requisito de seguridad a ser considerado como requisito funcional y de obligado cumplimiento e inclusi\ón en todos los sistemas de comunicaciones. Un inconveniente que presenta las t\écnicas criptogr\áficas, utilizadas para obtener la confidencialidad de la informaci\ón, surge cuando varias entidades se ven forzadas a compartir informaci\ón secreta para realizar tareas puntuales de colaboraci\ón, ya que las primitivas tradicionales utilizadas para conseguir la confidencialidad resultan poco flexibles. La situaci\ón ideal permitir\ía hacer posible dicha colaboraci\ón sin que ninguna de las partes revele la informaci\ón aportada. En este escenario entra en juego la tecnolog\ía de Computaci\ón Segura Multiparte (CSM) que posibilita realizar operaciones con la informaci\ón compartida sin tener que hacerla p\ública. Este trabajo muestra una soluci\ón CSM aplicada a una subasta electr\ónica que permite la realizaci\ón de la subasta sin que las apuestas sean reveladas a ning\ún participante, incluyendo el subastador, por lo que no necesita el estableciendo de ninguna autoridad confiable. Aunque la literatura ofrece una amplia variedad de propuestas te\óricas de CSM desde su creaci\ón en la d\écada de los ochenta, no es com\ún su aplicacion pr\áctica en situaciones reales.

}, author = {Jose A. Montenegro and Javier Lopez and Rene Peralta} } @article {Agudo2009, title = {Concurrent access control for multi-user and multi-processor systems based on trust relationships}, journal = {Concurrency and Computation: Practice and Experience}, volume = {21}, year = {2009}, month = {July}, pages = {1389-1403}, publisher = {John Wiley \& Sons}, abstract = {

Concurrent access control is an old problem in many fields in Computer Science. It has been solved in many languages and systems, using mechanisms like monitors or priority queues. Nowadays computers implement multi-core capabilities. This means that they are virtually capable of execution of processes in parallel. This requires new techniques and open new issues in the field of concurrent access control. Moreover, most operating systems are multi-user; thus, we have to focus on a multi-processor multi-user scenario. Trust becomes a paramount aspect when building distributed applications; the same applies on a lower scale in modern computers. We propose the use of a trust graph that keeps record of the trust relationships of the system and helps in deciding on concurrent access requests. The information encoded in the graph will be used both in order to decide on the access requests and to order granted requests in terms of their associated trust level

}, issn = {1532-0626}, doi = {10.1002/cpe.1430}, author = {Isaac Agudo and Carmen Fernandez-Gago and Javier Lopez} } @proceedings {1605, title = {Computer Security - ESORICS 2008, 13th European Symposium on Research in Computer Security, M{\'a}laga, Spain, October 6-8, 2008. Proceedings}, journal = {ESORICS}, volume = {5283}, year = {2008}, publisher = {Springer}, isbn = {978-3-540-88312-8}, editor = {Sushil Jajodia and Javier Lopez} } @proceedings {1607, title = {Computer Security - ESORICS 2007, 12th European Symposium On Research In Computer Security, Dresden, Germany, September 24-26, 2007, Proceedings}, journal = {ESORICS}, volume = {4734}, year = {2007}, publisher = {Springer}, isbn = {978-3-540-74834-2}, editor = {Joachim Biskup and Javier Lopez} } @proceedings {1606, title = {Critical Information Infrastructures Security, Second International Workshop, CRITIS 2007, M{\'a}laga, Spain, October 3-5, 2007. Revised Papers}, journal = {CRITIS}, volume = {5141}, year = {2007}, publisher = {Springer}, isbn = {978-3-540-89095-9}, doi = {10.1007/978-3-540-89173-4}, editor = {Javier Lopez and Bernhard M. H\"ammerli} } @proceedings {1610, title = {Critical Information Infrastructures Security, First International Workshop, CRITIS 2006, Samos, Greece, August 31 - September 1, 2006, Revised Papers}, journal = {CRITIS}, volume = {4347}, year = {2006}, publisher = {Springer}, isbn = {3-540-69083-2}, editor = {Javier Lopez} } @article {Roman2005f, title = {Casual Virtual Private Network}, journal = {International Journal of Computer Systems Science \& Engineering}, volume = {3}, year = {2005}, pages = {185-192}, publisher = {CRL Publishing}, abstract = {

Virtual Private Networks (VPNs) provide a cost-effective way for securing communications using public and insecure networks like the Internet. The main purpose of a VPN is to securely and transparently connect two or more remote networks to form virtually a single network, using centralized security policies for better management and protection. However, in certain scenarios, users may not require such a transparent access to the resources within their networks, but only want temporary secure access to internal services based on their own demands. We call the network architecture with such a feature as Casual VPN. In this paper, we present the notion of Casual VPN, and explain why traditional VPN architectures and protocols are unable to offer Casual VPN services. We also propose and define the operation of a particular Casual VPN architecture, C-VPN, which additionally allows the management of TCP and UDP-based protocols.

}, issn = {0267-6192}, author = {Rodrigo Roman and Jianying Zhou and Javier Lopez} } @inproceedings {JavierLopez2005a, title = {Classifying Public Key Certificates}, booktitle = {2nd European PKI Workshop: Research and Applications (EuroPKI{\textquoteright}05)}, series = {LNCS}, volume = {3545}, year = {2005}, month = {June}, pages = {135-143}, publisher = {Springer}, organization = {Springer}, address = {Canterbury, U.K.}, abstract = {

In spite of the fact that there are several companies that (try to) sell public key certificates, there is still no unified or standardized classification scheme that can be used to compare and put into perspective the various offerings. In this paper, we try to start filling this gap and propose a four-dimensional scheme that can be used to uniformly describe and classify public key certificates. The scheme distinguishes between (i) who owns a certificate, (ii) how the certificate owner is registered, (iii) on what medium the certificate (or the private key, respectively) is stored, and (iv) what type of functionality the certificate is intended to be used for. We think that using these or similar criteria to define and come up with unified or even standardized classes of public key certificate is useful and urgently needed in practice.

}, author = {Javier Lopez and Rolf Oppliger and Guenther Pernul} } @inproceedings {EijiOkamoto2003, title = {Certificate Retrieval and Validation in Online Systems}, booktitle = {Symposium on Cryptography and Information Security (SCIS{\textquoteright}03)}, year = {2003}, month = {January}, pages = {25-30}, address = {Hamamatsu, Japan}, abstract = {

In order to more effectively deal with certificate management issues in PKIs, there is growing interest in supplementing offline X.509 PKI models with online services. An analysis of the security requirements of online models will be presented. Proposed online and delegated processing models will be evaluated in relation to these requirements.

}, author = {Eiji Okamoto and Javier Lopez and Ed Dawson and Juan M. Gonzalez-Nieto and Selwyn Russell and Jason Smith} } @inproceedings {JavierLopez1999c, title = {Cert{\textquoteright}eM: Certification System Based on Electronic Mail Service Structure}, booktitle = {Secure Networking (CQRE{\textquoteright}99)}, series = {LNCS}, volume = {1740}, year = {1999}, month = {December}, pages = {109-118}, publisher = {Springer}, organization = {Springer}, abstract = {

Public-Key Infrastructures are considered the basis of the protocols and tools needed to guarantee the security demanded for new Internet applications like electronic commerce, government-citizen relationships and digital distribution. This paper introduces a new infrastructure design, Cert{\textquoteright}eM, a key management and certification system that is based on the structure of the electronic mail service and on the principle of near-certification. Cert{\textquoteright}eM provides secure means to identify users and distribute their public-key certificates, enhances the efficiency of revocation procedures, and avoids scalability and synchronization problems. The system, developed and tested at the University of Malaga, was recently selected by RedIRIS, the National Research and Academic Network in Spain, to provide the public key service for its secure electronic mail.

}, author = {Javier Lopez and Antonio Mana and Juan J. Ortega} } @inproceedings {AlfonsoLarrosa1999, title = {Competitive Neural Networks Applied to Image Compression Techniques}, booktitle = {International Conference on Imaging Science, Systems and Technology (CISST{\textquoteright}99)}, year = {1999}, month = {June}, pages = {547-550}, author = {Alfonso Larrosa and Francisco Lopez and Javier Lopez} } @article {JavierAretitio1999, title = {Contribuciones de la Tecnolog{\'\i}a de Detecci{\'o}n y Respuesta a Intrusiones y Ataques a la Construcci{\'o}n de la Confianza}, journal = {Nov{\'a}tica}, volume = {141}, year = {1999}, pages = {24-27}, author = {Javier Areitio and Javier Lopez} } @article {GonzaloRamos1998, title = {Comparisons of Parikh{\textquoteright}s conditions to other conditions for context-free languages}, journal = {Theoretical Computer Science}, volume = {202}, number = {1-2}, year = {1998}, pages = {231-244}, publisher = {Elsevier}, abstract = {

this paper we first compare Parikh\’s condition to various pumping conditions\ - Bar- Hillel\’s pumping lemma, Ogden\’s condition and Bader-Moura\’s condition; secondly, to interchange condition; and finally, to Sokolowski\’s and Grant\“s conditions. In order to carry out these comparisons we present some properties of Parikh\’s languages. The main result is the orthogonality of the previously mentioned conditions and Parikh\’s condition.

In

}, issn = {0304-3975}, author = {Gonzalo Ramos and Javier Lopez and Rafael Morales} } @inproceedings {JavierLopez1996a, title = {Comparaci{\'o}n de la Condici{\'o}n de Parikh con algunas Condiciones de los Lenguajes de Contexto Libre}, booktitle = {II Jornadas de Inform{\'a}tica y Autom{\'a}tica}, year = {1996}, month = {Julio}, pages = {305-314}, address = {Almu{\~n}ecar, Espa}, abstract = {

In this paper we first compare Parikh\’s condition to various pumping conditions - Bar-Hillel\’s pumping lemma, Ogden\’s condition and Bader-Moura\’s condition; secondly, to interchange condition; and finally, to Sokolowski\’s and Grant\’s conditions. In order to carry out these comparisons we present some properties of Parikh\’s languages. The main result is the orthogonality of the previously mentioned conditions and Parikh\’s condition.

}, author = {Javier Lopez and Gonzalo Ramos and Rafael Morales} }