XAdES4J: a java library for XAdES signature services

As comunicações electrónicas são cada vez mais o meio de eleição para negócios entre entidades e para as relações entre os cidadãos e o Estado (e-government). Esta diversidade de transacções envolve, muitas vezes, informação sensível e com possível valor legal. Neste contexto, as assinaturas electrónicas são uma importante base de confiança, fornecendo garantias de integridade e autenticação entre os intervenientes. A produção de uma assinatura digital resulta não só no valor da assinatura propriamente dita, mas também num conjunto de informação adicional acerca da mesma, como o algoritmo de assinatura, o certificado de validação ou a hora e local de produção. Num cenário heterogéneo como o descrito anteriormente, torna-se necessária uma forma flexível e interoperável de descrever esse tipo de informação. A linguagem XML é uma forma adequada de representar uma assinatura neste contexto, não só pela sua natureza estruturada, mas principalmente por ser baseada em texto e ter suporte generalizado. A recomendação XML Signature Syntax and Processing (ou apenas XML Signature) foi o primeiro passo na representação de assinaturas em XML. Nela são definidas sintaxe e regras de processamento para criar, representar e validar assinaturas digitais. As assinaturas XML podem ser aplicadas a qualquer tipo de conteúdos digitais identificáveis por um URI, tanto no mesmo documento XML que a assinatura, como noutra qualquer localização. Além disso, a mesma assinatura XML pode englobar vários recursos, mesmo de tipos diferentes (texto livre, imagens, XML, etc.). À medida que as assinaturas electrónicas foram ganhando relevância tornou-se evidente que a especificação XML Signature não era suficiente, nomeadamente por não dar garantias de validade a longo prazo nem de não repudiação. Esta situação foi agravada pelo facto da especificação não cumprir os requisitos da directiva 1999/93/EC da União Europeia, onde é estabelecido um quadro legal para as assinaturas electrónicas a nível comunitário. No seguimento desta directiva da União Europeia foi desenvolvida a especificação XML Advanced Electronic Signatures que define formatos XML e regras de processamento para assinaturas electrónicas não repudiáveis e com validade verificável durante períodos de tempo extensos, em conformidade com a directiva. Esta especificação estende a recomendação XML Signature, definindo novos elementos que contêm informação adicional acerca da assinatura e dos recursos assinados (propriedades qualificadoras). A plataforma Java inclui, desde a versão 1.6, uma API de alto nível para serviços de assinaturas digitais em XML, de acordo com a recomendação XML Signature. Contudo, não existe suporte para assinaturas avançadas. Com este projecto pretende-se desenvolver uma biblioteca Java para a criação e validação de assinaturas XAdES, preenchendo assim a lacuna existente na plataforma. A biblioteca desenvolvida disponibiliza uma interface com alto nível de abstracção, não tendo o programador que lidar directamente com a estrutura XML da assinatura nem com os detalhes do conteúdo das propriedades qualificadoras. São definidos tipos que representam os principais conceitos da assinatura, nomeadamente as propriedades qualificadoras e os recursos assinados, sendo os aspectos estruturais resolvidos internamente. Neste trabalho, a informação que compõe uma assinatura XAdES é dividia em dois grupos: o primeiro é formado por características do signatário e da assinatura, tais como a chave e as propriedades qualificadoras da assinatura. O segundo grupo é composto pelos recursos assinados e as correspondentes propriedades qualificadoras. Quando um signatário produz várias assinaturas em determinado contexto, o primeiro grupo de características será semelhante entre elas. Definiu-se o conjunto invariante de características da assinatura e do signatário como perfil de assinatura. O conceito é estendido à verificação de assinaturas englobando, neste caso, a informação a usar nesse processo, como por exemplo os certificados raiz em que o verificador confia. Numa outra perspectiva, um perfil constitui uma configuração do serviço de assinatura correspondente. O desenho e implementação da biblioteca estão também baseados no conceito de fornecedor de serviços. Um fornecedor de serviços é uma entidade que disponibiliza determinada informação ou serviço necessários à produção e verificação de assinaturas, nomeadamente: selecção de chave/certificado de assinatura, validação de certificados, interacção com servidores de time-stamp e geração de XML. Em vez de depender directamente da informação em causa, um perfil — e, consequentemente, a operação correspondente — é configurado com fornecedores de serviços que são invocados quando necessário. Para cada tipo de fornecedor de serviços é definida um interface, podendo as correspondentes implementações ser configuradas de forma independente. A biblioteca inclui implementações de todos os fornecedores de serviços, sendo algumas delas usadas for omissão na produção e verificação de assinaturas. Uma vez que o foco do projecto é a especificação XAdES, o processamento e estrutura relativos ao formato básico são delegados internamente na biblioteca Apache XML Security, que disponibiliza uma implementação da recomendação XML Signature. Para validar o funcionamento da biblioteca, nomeadamente em termos de interoperabilidade, procede-se, entre outros, à verificação de um conjunto de assinaturas produzidas por Estados Membros da União Europeia, bem como por outra implementação da especificação XAdES

Proposed Model for Outsourcing PKI

PKI is often referred to as a pervasive substrate. This terminology is used to describe the technological layer that permeates the entirety of the organisation on which PKI services are established. From the mid 1970s when Whitfield Diffie and Martin Hellman published their paper New Directions in Cryptography the concept of Public Key Cryptography, for the first time, allowed two entities with no previous relationship to communicate secure information over unsecured channels. PKI provides the infrastructure that allows Public Key Cryptography to function within a hierarchical structure, providing between two entities, an acceptable level of trust. Outsourcing is the process of acquiring sources or services from an external source. With the modular structure of today's organisations it can also mean that goods and services can be procured from one segment of the organisation to another through inhouse service-supplier agreements. Outsourcing has evolved from the days of heavy industry and manufacturing in the 1960s to the total solution management of today. This dissertation brings together the concepts of both PKI and Outsourcing. It details our AB-5C Model for organisations to outsource a PKI system within the scope of the businesses strategic goals and objectives. Our proposed model takes into account the need to use existing models, procedures and practices in support of an outsourced PKI Model. These include a process or processes to ensure that any outsourced solution adds value to the organisation, and that there is a business strategy that allows the alignment of the outsourcing strategy to the organisations strategic plan

UNIQuE: A User-Centric Framework for Network Identity Management

Network identity management system, in theory, is conceived as the solution to many identity-related issues burgeoning day-to-day. These issues, which need to be addressed, range from managing the outburst of user identities to protecting user interests as well as business interests. This paper proposes a framework for network identity management on the Internet that addresses these issues from a user-centric point of view. After discussing the challenges and opportunities of a user-centric identity management system, we describe the architecture of our framework called UNIQuE in detail. The architecture comprises components such as a security infrastructure, a trust subsystem, an inter-provider communication system, and a repository system. In essence, the goal of this framework is to specify a comprehensive, user-centric solution to all identity-related issues, which also vouches for effortless maintenance. The fundamental difference to existing systems is its integrating approach to many usually separately considered, identity-related issues

Software-implemented attack tolerance for critical information retrieval

The fast-growing reliance of our daily life upon online information services often demands an appropriate level of privacy protection as well as highly available service provision. However, most existing solutions have attempted to address these problems separately. This thesis investigates and presents a solution that provides both privacy protection and fault tolerance for online information retrieval. A new approach to Attack-Tolerant Information Retrieval (ATIR) is developed based on an extension of existing theoretical results for Private Information Retrieval (PIR). ATIR uses replicated services to protect a user's privacy and to ensure service availability. In particular, ATIR can tolerate any collusion of up to t servers for privacy violation and up to ƒ faulty (either crashed or malicious) servers in a system with k replicated servers, provided that k ≥ t + ƒ + 1 where t ≥ 1 and ƒ ≤ t. In contrast to other related approaches, ATIR relies on neither enforced trust assumptions, such as the use of tanker-resistant hardware and trusted third parties, nor an increased number of replicated servers. While the best solution known so far requires k (≥ 3t + 1) replicated servers to cope with t malicious servers and any collusion of up to t servers with an O(n^*^) communication complexity, ATIR uses fewer servers with a much improved communication cost, O(n1/2)(where n is the size of a database managed by a server).The majority of current PIR research resides on a theoretical level. This thesis provides both theoretical schemes and their practical implementations with good performance results. In a LAN environment, it takes well under half a second to use an ATIR service for calculations over data sets with a size of up to 1MB. The performance of the ATIR systems remains at the same level even in the presence of server crashes and malicious attacks. Both analytical results and experimental evaluation show that ATIR offers an attractive and practical solution for ever-increasing online information applications

Actas da 10ª Conferência sobre Redes de Computadores

Universidade do MinhoCCTCCentro AlgoritmiCisco SystemsIEEE Portugal Sectio

Multi-agent system security for mobile communication

This thesis investigates security in multi-agent systems for mobile communication. Mobile as well as non-mobile agent technology is addressed. A general security analysis based on properties of agents and multi-agent systems is presented along with an overview of security measures applicable to multi-agent systems, and in particular to mobile agent systems. A security architecture, designed for deployment of agent technology in a mobile communication environment, is presented. The security architecture allows modelling of interactions at all levels within a mobile communication system. This architecture is used as the basis for describing security services and mechanisms for a multi-agent system. It is shown how security mechanisms can be used in an agent system, with emphasis on secure agent communication. Mobile agents are vulnerable to attacks from the hosts on which they are executing. Two methods for dealing with threats posed by malicious hosts to a trading agent are presented. The rst approach uses a threshold scheme and multiple mobile agents to minimise the eect of malicious hosts. The second introduces trusted nodes into the infrastructure. Undetachable signatures have been proposed as a way to limit the damage a malicious host can do by misusing a signature key carried by a mobile agent. This thesis proposes an alternative scheme based on conventional signatures and public key certicates. Threshold signatures can be used in a mobile agent scenario to spread the risk between several agents and thereby overcome the threats posed by individual malicious hosts. An alternative to threshold signatures, based on conventional signatures, achieving comparable security guarantees with potential practical advantages compared to a threshold scheme is proposed in this thesis. Undetachable signatures and threshold signatures are both concepts applicable to mobile agents. This thesis proposes a technique combining the two schemes to achieve undetachable threshold signatures. This thesis denes the concept of certicate translation, which allows an agent to have one certicate translated into another format if so required, and thereby save storage space as well as being able to cope with a certicate format not foreseen at the time the agent was created

Enhancing the reliability of digital signatures as non-repudiation evidence under a holistic threat model

Traditional sensitive operations, like banking transactions, purchase processes, contract agreements etc. need to tie down the involved parties respecting the commitments made, avoiding a further repudiation of the responsibilities taken. Depending on the context, the commitment is made in one way or another, being handwritten signatures possibly the most common mechanism ever used. With the shift to digital communications, the same guarantees that exist in real world transactions are expected from electronic ones as well. Non-repudiation is thus a desired property of current electronic transactions, like those carried out in Internet banking, e-commerce or, in general, any electronic data interchange scenario. Digital evidence is generated, collected, maintained, made available and verified by non-repudiation services in order to resolve disputes about the occurrence of a certain event, protecting the parties involved in a transaction against the other's false denial about such an event. In particular, a digital signature is considered as non-repudiation evidence which can be used subsequently, by disputing parties or by an adjudicator, to arbitrate in disputes. The reliability of a digital signature should determine its capability to be used as valid evidence. The reliability depends on the trustworthiness of the whole life cycle of the signature, including the generation, transfer, verification and storage phases. Any vulnerability in it would undermine the reliability of the digital signature, making its applicability as non-repudiation evidence dificult to achieve. Unfortunately, technology is subject to vulnerabilities, always with the risk of an occurrence of security threats. Despite that, no rigorous mechanism addressing the reliability of digital signatures technology has been proposed so far. The main goal of this doctoral thesis is to enhance the reliability of digital signatures in order to enforce their non-repudiation property when acting as evidence. In the first instance, we have determined that current technology does not provide an acceptable level of trustworthiness to produce reliable nonrepudiation evidence that is based on digital signatures. The security threats suffered by current technology are suffice to prevent the applicability of digital signatures as non-repudiation evidence. This finding is also aggravated by the fact that digital signatures are granted legal effectiveness under current legislation, acting as evidence in legal proceedings regarding the commitment made by a signatory in the signed document. In our opinion, the security threats that subvert the reliability of digital signatures had to be formalized and categorized. For that purpose, a holistic taxonomy of potential attacks on digital signatures has been devised, allowing their systematic and rigorous classification. In addition, and assuming a realistic security risk, we have built a new approach more robust and trustworthy than the predecessors to enhance the reliability of digital signatures, enforcing their non-repudiation property. This new approach is supported by two novel mechanisms presented in this thesis: the signature environment division paradigm and the extended electronic signature policies. Finally, we have designed a new fair exchange protocol that makes use of our proposal, demonstrating the applicability in a concrete scenario. ----------------------------------------------------------------------------------------------------------------------------------------------------------------Las operaciones sensibles tradicionales, tales como transacciones bancarias, procesos de compra-venta, firma de contratos etc. necesitan que las partes implicadas queden sujetas a los compromisos realizados, evitando así un repudio posterior de las responsabilidades adquiridas. Dependiendo del contexto, el compromiso se llevaría a cabo de una manera u otra, siendo posiblemente la firma manuscrita el mecanismo más comúnmente empleado hasta la actualidad. Con el paso a las comunicaciones digitales, se espera que las mismas garantías que se encuentran en las transacciones tradicionales se proporcionen también en las electrónicas. El no repudio es, por tanto, una propiedad deseada a las actuales transacciones electrónicas, como aquellas que se llevan a cabo en la banca online, en el comercio electrónico o, en general, en cualquier intercambio de datos electrónico. La evidencia digital se genera, recoge, mantiene, publica y verifica mediante los servicios de no repudio con el fin de resolver disputas acerca de la ocurrencia de un determinado evento, protegiendo a las partes implicadas en una transacción frente al rechazo respecto a dicho evento que pudiera realizar cualquiera de las partes. En particular, una firma digital se considera una evidencia de no repudio que puede emplearse posteriormente por las partes enfrentadas o un tercero durante el arbitrio de la disputa. La fiabilidad de una firma digital debería determinar su capacidad para ser usada como evidencia válida. Dicha fiabilidad depende de la seguridad del ciclo de vida completo de la firma, incluyendo las fases de generación, transferencia, verificación, almacenamiento y custodia. Cualquier vulnerabilidad en dicho proceso podría socavar la fiabilidad de la firma digital, haciendo difícil su aplicación como evidencia de no repudio. Desafortunadamente, la tecnología está sujeta a vulnerabilidades, existiendo siempre una probabilidad no nula de ocurrencia de amenazas a su seguridad. A pesar de ello, hasta la fecha no se ha propuesto ningún mecanismo que aborde de manera rigurosa el estudio de la fiabilidad real de la tecnología de firma digital. El principal objetivo de esta tesis doctoral es mejorar la fiabilidad de las firmas digitales para que éstas puedan actuar como evidencia de no repudio con garantías suficientes