Breaking and Fixing Anonymous Credentials for the Cloud

In an attribute-based credential (ABC) system, users obtain a digital certificate on their personal attributes, and can later prove possession of such a certificate in an unlinkable way, thereby selectively disclosing chosen attributes to the service provider. Recently, the concept of encrypted ABCs (EABCs) was introduced by Krenn et al. at CANS 2017, where virtually all computation is outsourced to a semi-trusted cloud-provider called wallet, thereby overcoming existing efficiency limitations on the user’s side, and for the first time enabling “privacy-preserving identity management as a service”. While their approach is highly relevant for bringing ABCs into the real world, we present a simple attack allowing the wallet to learn a user\u27s attributes when colluding with another user -- a scenario which is not covered by their modeling but which needs to be considered in practice. We then revise the model and construction of Krenn et al. in various ways, such that the above attack is no longer possible. Furthermore, we also remove existing non-collusion assumptions between wallet and service provider or issuer from their construction. Our protocols are still highly efficient in the sense that the computational effort on the end user side consists of a single exponentiation only, and otherwise efficiency is comparable to the original work of Krenn et al

{SoK}: {An} Analysis of Protocol Design: Avoiding Traps for Implementation and Deployment

Today's Internet utilizes a multitude of different protocols. While some of these protocols were first implemented and used and later documented, other were first specified and then implemented. Regardless of how protocols came to be, their definitions can contain traps that lead to insecure implementations or deployments. A classical example is insufficiently strict authentication requirements in a protocol specification. The resulting Misconfigurations, i.e., not enabling strong authentication, are common root causes for Internet security incidents. Indeed, Internet protocols have been commonly designed without security in mind which leads to a multitude of misconfiguration traps. While this is slowly changing, to strict security considerations can have a similarly bad effect. Due to complex implementations and insufficient documentation, security features may remain unused, leaving deployments vulnerable. In this paper we provide a systematization of the security traps found in common Internet protocols. By separating protocols in four classes we identify major factors that lead to common security traps. These insights together with observations about end-user centric usability and security by default are then used to derive recommendations for improving existing and designing new protocols---without such security sensitive traps for operators, implementors and users

Federated identity architecture of the european eID system

Federated identity management is a method that facilitates management of identity processes and policies among the collaborating entities without a centralized control. Nowadays, there are many federated identity solutions, however, most of them covers different aspects of the identification problem, solving in some cases specific problems. Thus, none of these initiatives has consolidated as a unique solution and surely it will remain like that in a near future. To assist users choosing a possible solution, we analyze different federated identify approaches, showing main features, and making a comparative study among them. The former problem is even worst when multiple organizations or countries already have legacy eID systems, as it is the case of Europe. In this paper, we also present the European eID solution, a purely federated identity system that aims to serve almost 500 million people and that could be extended in midterm also to eID companies. The system is now being deployed at the EU level and we present the basic architecture and evaluate its performance and scalability, showing that the solution is feasible from the point of view of performance while keeping security constrains in mind. The results show a good performance of the solution in local, organizational, and remote environments

{SoK}: {An} Analysis of Protocol Design: Avoiding Traps for Implementation and Deployment

Today's Internet utilizes a multitude of different protocols. While some of these protocols were first implemented and used and later documented, other were first specified and then implemented. Regardless of how protocols came to be, their definitions can contain traps that lead to insecure implementations or deployments. A classical example is insufficiently strict authentication requirements in a protocol specification. The resulting Misconfigurations, i.e., not enabling strong authentication, are common root causes for Internet security incidents. Indeed, Internet protocols have been commonly designed without security in mind which leads to a multitude of misconfiguration traps. While this is slowly changing, to strict security considerations can have a similarly bad effect. Due to complex implementations and insufficient documentation, security features may remain unused, leaving deployments vulnerable. In this paper we provide a systematization of the security traps found in common Internet protocols. By separating protocols in four classes we identify major factors that lead to common security traps. These insights together with observations about end-user centric usability and security by default are then used to derive recommendations for improving existing and designing new protocols---without such security sensitive traps for operators, implementors and users

Token Based Authentication and Authorization with Zero-Knowledge Proofs for Enhancing Web API Security and Privacy

This design science study showcases an innovative artifact that utilizes Zero-Knowledge Proofs for API Authentication and Authorization. A comprehensive examination of existing literature and technology is conducted to evaluate the effectiveness of this alternative approach. The study reveals that existing APIs are using slower techniques that don’t scale, can’t take advantage of newer hardware, and have been unable to adequately address current security issues. In contrast, the novel technique presented in this study performs better, is more resilient in privacy sensitive and security settings, and is easy to implement and deploy. Additionally, this study identifies potential avenues for further research that could help advance the field of Web API development in terms of security, privacy, and simplicity

Secure Software Development in the Era of Fluid Multi-party Open Software and Services

Pushed by market forces, software development has become fast-paced. As a consequence, modern development projects are assembled from 3rd-party components. Security & privacy assurance techniques once designed for large, controlled updates over months or years, must now cope with small, continuous changes taking place within a week, and happening in sub-components that are controlled by third-party developers one might not even know they existed. In this paper, we aim to provide an overview of the current software security approaches and evaluate their appropriateness in the face of the changed nature in software development. Software security assurance could benefit by switching from a process-based to an artefact-based approach. Further, security evaluation might need to be more incremental, automated and decentralized. We believe this can be achieved by supporting mechanisms for lightweight and scalable screenings that are applicable to the entire population of software components albeit there might be a price to pay.Comment: 7 pages, 1 figure, to be published in Proceedings of International Conference on Software Engineering - New Ideas and Emerging Result

Issuer-Hiding Attribute-Based Credentials

Attribute-based credential systems enable users to authenticate in a privacy-preserving manner. However, in such schemes verifying a user\u27s credential requires knowledge of the issuer\u27s public key, which by itself might already reveal private information about the user. In this paper, we tackle this problem by introducing the notion of issuer-hiding attribute-based credential systems. In such a system, the verifier can define a set of acceptable issuers in an ad-hoc manner, and the user can then prove that her credential was issued by one of the accepted issuers -- without revealing which one. We then provide a generic construction, as well as a concrete instantiation based on Groth\u27s structure preserving signature scheme (ASIACRYPT\u2715) and simulation-sound extractable NIZK, for which we also provide concrete benchmarks in order to prove its practicability. The online complexity of all constructions is independent of the number of acceptable verifiers, which makes it also suitable for highly federated scenarios