a b s t r a c tThe interleaving of chaos and cryptography has been the aim of a large set of works since the beginning of the nineties. Many encryption proposals have been introduced to improve conventional cryptography. However, many of possess serious problems according to the basic requirements for the secure exchange of information. In this paper we highlight some of the main problems of chaotic cryptography by means of the analysis of a very recent chaotic cryptosystem based on a one round Substitution Permutation Network. More specifically, we show that it is not possible to avoid the security problems of that encryption architecture just by including a chaotic system as the core of the derived encryption system.

We propose a methodology for verifying security properties of network protocols at design level. It can be separated in two main parts: context and requirements analysis and informal verification; and formal representation and procedural verification. It is an iterative process where the early steps are simpler than the last ones. Therefore, the effort required for detecting flaws is proportional to the complexity of the associated attack. Thus, we avoid wasting valuable resources for simple flaws that can be detected early in the verification process. In order to illustrate the advantages provided by our methodology, we also analyze three real protocols.

Esta es la versión de autor de la comunicación de congreso publicada en: This is an author produced version of a paper published in: Abstract. The current technological scenario determines a profileration of trust domains, which are usually defined by validating the digital identity linked to each user. This validation entails critical assumptions about the way users' privacy is handled, and this calls for new methods to construct and treat digital identities. Considering cryptography, identity management has been constructed and managed through conventional digital signatures. Nowadays, new types of digital signatures are required, and this transition should be guided by rigorous evaluation of the theoretical basis, but also by the selection of properly verified software means. This latter point is the core of this paper. We analyse the main non-conventional digital signatures that could endorse an adequate tradeoff betweeen security and privacy. This discussion is focused on practical software solutions that are already implemented and available online. The goal is to help security system designers to discern identity management functionalities through standard cryptographic software libraries.

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Current anonymizing networks have become an important tool for guaranteeing users' privacy. However, these platforms can be used to perform illegitimate actions, which sometimes makes service providers see traffic coming from these networks as a probable threat. In order to solve this problem, we propose to add support for fairness mechanisms to the Tor network. Specifically, by introducing a slight modification to the key negotiation process with the entry and exit nodes, in the shape of group signatures. By means of these signatures, we set up an access control method to prevent misbehaving users to make use of the Tor network. Additionally, we establish a predefined method for denouncing illegitimate actions, which impedes the application of the proposed fairness mechanisms as a threat eroding users' privacy. As a direct consequence, traffic coming from Tor would be considered less suspicious by service providers.