Catálogo de publicaciones - libros

Electronic mail is one of the most used and abused service in today communication. While many efforts have been made to fight e-mail abuses, no effective solution has yet been developed. Furthermore new technologies (e.g. wireless roaming) and new user needs (e.g. mobility) completely break the existing e-mail authentication techniques based on network topology. In this paper we present the E-Mail Policy Enforcer system (EMPE) which provides a method to cryptographically bind the identity of the original sender of an e-mail to the message body by combining digital signatures and transport level authentication data.

DomainKeys Identified Mail is an anti-spam proposal that involves mail servers digitally signing outbound email and verifying signatures on inbound email. The scheme makes no use of existing public key infrastructure or email security standards. This paper provides an outline of the scheme and discusses some reasons why re-use of existing standards is inappropriate in this context.

Despite the introduction of information technologies in governmental administrations, most bureaucratic processes are still paper-based. In this paper we present a framework to transfer conventional, paper-based processes to electronic workflows. Thereby, the transformation to e-Government applications has two challenges. First, to find an equivalent description for the single activities and their interaction for defining the entire process. Second, to ensure the security of the process. We identified four types of activities that can be used as basic components for the workflows considered in our work. The security aspects of the electronic representation are ensured by further framework components, for example authentication or authorization. Finally, we present how this framework can be used for other scenarios and discuss some details of our prototype implementation.

Multimedia content distribution has appeared as a new growth market offered by network providers, defining resource access infrastructures able to support both wired and wireless accesses. Although these infrastructures have been widely studied in the last years, the main aim of those works has been focused more on the distribution process than on a suitable security infrastructure to protect that content. Therefore, the study of security systems able to offer authentication, authorization and other security-related requirements for those kinds of scenarios is still an open research field. In this paper, we propose a new scheme which takes advantage of a previously existing underlying authorization infrastructure among the involved organizations, the NAS-SAML system, to build a multimedia content distribution with an advanced and extensible authorization mechanism. The target scenario is the one proposed by the VIDIOS project, which defines an architecture for multimedia transmissions across error prone networks such as Internet backbones and mobile access networks.

We study conjunctive keyword search scheme allowing for remote search of data containing each of several keywords on encrypted data storage system. A data supplier first uploads encrypted data on a storage system, and then a user of the storage system searches data containing keywords over encrypted data hence insider (such as an administrator of the storage system) and outsider attackers do not learn anything else about the data. Recently, Golle et al . first suggested conjunctive keyword search scheme, but the communication and storage costs linearly depend on the number of stored data in the database, hence it is not really suitable for a large scale database. In this paper, we propose an efficient conjunctive keyword search scheme over encrypted data in aspects of communication and storage costs. Concretely, we reduce the storage cost of a user and the communication cost between a user and a data supplier to the constant amounts. We formally define security model for a conjunctive keyword search scheme and prove that the proposed scheme is secure under the decisional bilinear Diffie-Hellman (DBDH) assumption in the random oracle model.

In 2006, Wang-Li proposed a new user authentication scheme using smart cards which can offer forward secrecy. However, this paper will demonstrate that Wang-Li’s scheme is vulnerable to parallel session attack and reflection attack. Furthermore, the current paper presents a more efficient and secure scheme that not only resolves such problems, but also involves fewer computations and communications than Wang-Li’s scheme.

Conventional PKI is the most effective and efficient solution to non-repudiation. But, it also puts user privacy in danger because the user’s activities could be tracked via the unique public-key and certificate he presents in multiple transactions. Pseudonymous PKI (PPKI) solution achieves non-repudiation as well as privacy protection at the same time by providing Pseudonymous Public-Key (PPK) and Pseudonymous Certificate (PCert) that are computed by the user without CA intervention. PPK is as effective as conventional public-key in terms of non-repudiation. Furthermore, the PPKI solution is very efficient in terms of the size of PPK and PCert, and is scalable in terms of certification authority overhead. Therefore PPKI is particularly suitable for ubiquitous computing environments where authenticity, non-repudiation, privacy protection, efficiency, and scalability are key requirements.

WAP Forum recommends to use WTLS handshake protocol and signText() function to certify the POP (proof of possession) of authentication key and signing key. However, it causes plenty of computation and communication overload to mobile devices with low computation and communication power. In this paper, we propose an efficient POP confirmation protocol based on the signcryption scheme, which requires less computation and communication cost. It would be useful for the wireless and wired PKI. The proposed protocol is based on Zheng’s signcryption scheme, because it is the first and only signcryption scheme submitted to the international standard institute(IEEE p1363).

Key agreement protocols are a fundamental building block for ensuring authenticated and private communications between two parties over an insecure network. This paper focuses on key agreement protocols in the asymmetric trust model, wherein parties hold a public/private key pair. In particular, we consider a type of known key attack called key compromise impersonation that may occur once the adversary has obtained the private key of an honest party. This attack represents a subtle threat that is often underestimated and difficult to counter. Several protocols are shown vulnerable to this attack despite their authors claiming the opposite. We also consider in more detail how three formal (complexity-theoretic based) models of distributed computing found in the literature cover such attacks.

Dodis et al proposed a key-insulated signature scheme in 2003. The scheme can minimize the damage caused by the secret key’s exposure but can not protect the user from the secret key’s exposure perfectly. We propose a PKI system which can detect immediately even a single illegitimate signature due to the exposure of a user’s secret key. The system uses the one-time hash chain based on NOVOMODO and can prevent the users from compromising the secret key more perfectly and effectively than the key-insulated signature scheme.