The transition from centralized identity architecture to a decentralized one introduces profound shifts in the privacy protection of users’ data. Yet, as decentralized identity continues to mature, today’s online services still overwhelmingly depend on centralized and federated identity management solutions built on top of OpenID Connect (OIDC) as the most widespread solution. Ensuring privacy-preserving OIDC deployments is therefore critical for safeguarding users’ personal data and maintaining compliance with regulatory frameworks such as the General Data Protection Regulation (GDPR) and trust frameworks such as the Electronic Identification, Authentication and Trust Services (eIDAS). However, the current OIDC ecosystem lacks a coherent set of privacy Best Current Practices (BCPs) and a study of how widely these privacy-enhancing features are adopted in real-world deployments. To this end, this work addresses the aforementioned gaps on two fronts. First, we propose a structured set of privacy BCPs derived from official OIDC specifications and current implementation trends, identifying easy-to-deploy privacy-enhancing features that strengthen the OIDC deployments’ baseline privacy without altering the protocol or compromising interoperability. Furthermore, the BCPs also help achieve the GDPR privacy principles, such as data minimization, confidentiality, and unlinkability. Second, this work provides a comprehensive survey of OpenID Providers (OPs) in the wild to identify gaps in privacy-preserving configurations in both private and public (i.e., national) sectors OPs. The study employs a dual methodology: first, a manual review performed in 2022; subsequently, an automated compliance analysis performed in 2025 surveying a dataset of 10000 OPs worldwide. The results reveal a concerning lack of privacy-enhancing features among private OPs and a wide gap between private and national OPs, with the latter group providing, on average, much higher baseline privacy. We have also found a prevalence of OPs not complying with the OIDC specifications, resulting in misconfigured OPs hampering interoperability and, in some cases, security. The paper emphasizes the importance of adopting actionable BCPs to improve baseline privacy and demonstrates the need for an automated framework for ongoing privacy compliance assessments in OIDC ecosystems.

Cryptographic Access Control (CAC) allows organizations to control cloud-hosted data sharing among users while preventing external attackers, malicious insiders, and honest-but-curious cloud providers from accessing the data. However, CAC entails an overhead often impractical for real-world scenarios due to the many cryptographic computations involved. Hence, we put forth a hybrid Access Control (AC) scheme --- combining CAC and (traditional) centralized AC --- that considers trust assumptions (e.g., on users) and data protection requirements of the underlying scenario on a case-by-case basis to reduce the number of cryptographic computations to execute in CAC. Besides, we design a consistency check to ensure the correctness and safety properties of the enforcement of the hybrid AC scheme, provide a proof-of-concept implementation in Prolog, and conduct a preliminary experimental evaluation.

The Single Sign-On based account linking process (SSOLinking in short) allows users to link their accounts at Service Provider (SP) websites to their Identity Providers (IdP) accounts. We focus on a serious (and overlooked) attack, namely an Account Hijack targeting the SSOLinking and relying on two CSRF vulnerabilities, one affecting the IdP and the other the SP. The former is an Authentication CSRF (also known as Login CSRF) and the latter is a CSRF on the button triggering the SSOLinking. We propose a security testing approach to help testers automatically detect such attacks. We implemented our testing technique as an extension (namely SSOLinking Checker) to the open-source penetration testing tool Micro-Id-Gym. To demonstrate the effectiveness of our approach and the pervasiveness of the SSOLinking Account Hijack, we conducted an experimental analysis against a selection of popular SPs that offer the SSOLinking with major IdPs. The results of our experiments are alarming: out of the 648 web sites we considered, 48 qualified for conducting our experiments and 21 of these suffered from SSOLinking vulnerability (i.e. 43.7%). Our findings (we responsibly disclosed to the affected vendors) include severe vulnerabilities among the web sites of Goodreads, Naver, Workable, etc.

Authentication protocols represent the entry point to online services, so they must be sturdily designed in order to allow only authorized users to access the underlying data. However, designing authentication protocols is a complex process: security designers should carefully select the technologies to involve and integrate them properly in order to prevent potential vulnerabilities. In addition, these choices are usually restricted by further factors, such as the requirements associated with the scenario, the regulatory framework, the dimensions to balance (e.g., security vs. usability), and the standards to rely on. We come to the rescue by presenting an automated multi-layered methodology we have developed to assist security designers in this phase: by repeatedly evaluating their protocols, they can select the security mitigations to consider until they reach the desired security level, thus enabling a security-by-design approach. For concreteness, we also show how we have applied our methodology to a real use case scenario in the context of a collaboration with the Italian Government Printing Office and Mint.

An Attribute Authority is an entity responsible for establishing, maintaining, and sharing a subject’s qualified attributes, such as titles and qualifications. In the OpenID Connect digital identity ecosystem, In the OpenID Connect digital identity ecosystem, for privacy reasons, this entity is distinct from Identity Providers that manage only the basic identity profile information. A relevant scenario is as follows: the User first logs in to an online service using his/her identity managed by an Identity Provider. Then, the online service asks the Attribute Authority for the additional User’s attributes (e.g., entitlements) before granting access to its resources. In some high-sensitive cases, an Attribute Authority needs proof of the User’s authentication before releasing the User’s attributes to the online service. The challenge of this scenario involving usability, security, and privacy requirements lies in finding the right mechanism to share (the minimum and necessary set of) claims of the User who is currently authenticated with the online service across multiple domains without requiring his or her re-authentication. In this paper, we present the design of two solutions based on OpenID Connect to share User claims across domains. We provide security and privacy analysis for the two solutions and a brief comparison between them.

The eIDAS Regulation aims to provide an interoperable European framework to enable EU citizens to authenticate and communicate with services of other Member States by using their national electronic identity. While a set of high-level requirements (e.g., related to privacy and security) are established to make interoperability among Member States possible, the eIDAS Regulation does not explicitly specify the technologies that can be adopted during the development phase to meet the requirements as mentioned earlier. This paper considers the technological trends of (pre)notified eIDAS electronic identity schemes used by Member States, and they satisfy the eIDAS regulation requirements. We do this by defining a set of research questions that allow us to investigate the correlations between different design dimensions such as security, privacy, and usability. Based on these findings, we provide a set of lessons learned that can be used by the security community to protect interoperable national digital identities more efficiently.

To facilitate the adoption of cloud by organizations, Cryptographic Access Control (CAC) is the obvious solution to control data sharing among users while preventing partially trusted Cloud Service Providers (CSP) from accessing sensitive data. Indeed, several CAC schemes have been proposed in the literature. Despite their differences, available solutions are based on a common set of entities—e.g., a data storage service or a proxy mediating the access of users to encrypted data—that operate in different (security) domains—e.g., on-premise or the CSP. However, the majority of these CAC schemes assumes a fixed assignment of entities to domains; this has security and usability implications that are not made explicit and can make inappropriate the use of a CAC scheme in certain scenarios with specific trust assumptions and requirements. For instance, assuming that the proxy runs at the premises of the organization avoids the vendor lock-in effect but may give rise to other security concerns (e.g., malicious insiders attackers). To the best of our knowledge, no previous work considers how to select the best possible architecture (i.e., the assignment of entities to domains) to deploy a CAC scheme for the trust assumptions and requirements of a given scenario. In this article, we propose a methodology to assist administrators in exploring different architectures for the enforcement of CAC schemes in a given scenario. We do this by identifying the possible architectures underlying the CAC schemes available in the literature and formalizing them in simple set theory. This allows us to reduce the problem of selecting the most suitable architectures satisfying a heterogeneous set of trust assumptions and requirements arising from the considered scenario to a decidable Multi-objective Combinatorial Optimization Problem (MOCOP) for which state-of-the-art solvers can be invoked. Finally, we show how we use the capability of solving the MOCOP to build a prototype tool assisting administrators to preliminarily perform a “What-if” analysis to explore the trade-offs among the various architectures and then use available standards and tools (such as TOSCA and Cloudify) for automated deployment in multiple CSPs.

While organisations move their infrastructure to the cloud, honest but curious Cloud Service Providers (CSPs) threaten the confidentiality of cloud-hosted data. In this context, many researchers proposed Cryptographic Access Control (CAC) schemes to support data sharing among users while preventing CSPs from accessing sensitive data. However, the majority of these schemes focuses on high-level features only and cannot adapt to the multiple requirements arising in different scenarios. Moreover, (almost) no CAC scheme implementation is available for enforcement of authorisation policies in the cloud, and performance evaluation is often overlooked. To fill this gap, we propose the toolchain COERCIVE, short for CryptOgraphy killEd (the honest but) cuRious Cloud servIce proVidEr, which is composed of two tools: TradeOffBoard and CryptoAC. TradeOffBoard assists organisations in identifying the optimal CAC architecture for their scenario. CryptoAC enforces authorisation policies in the cloud by deploying the architecture selected with TradeOffBoard. In this paper, we describe the implementation of CryptoAC and conduct a thorough performance evaluation to demonstrate its scalability and efficiency with synthetic benchmarks.

To facilitate the adoption of cloud by organizations, Cryptographic Access Control (CAC) is the obvious solution to control data sharing among users while preventing partially trusted Cloud Service Providers (CSP) from accessing sensitive data. Indeed, several CAC schemes have been proposed in the literature. Despite their differences, available solutions are based on a common set of entities---e.g., a data storage service or a proxy mediating the access of users to encrypted data---that operate in different (security) domains---e.g., on-premise or the CSP. However, the majority of the CAC schemes assume a fixed assignment of entities to domains; this has security and usability implications that are not made explicit and can make inappropriate the use of a CAC scheme in certain scenarios with specific requirements. For instance, assuming that the proxy runs at the premises of the organization avoids the vendor lock-in effect but may substantially undermine scalability.

Everyday life is permeated by new technologies allowing people to perform almost any kind of operation from their smart devices. Although this is amazing from a convenience perspective, it may result in several security issues concerning the need for authenticating users in a proper and secure way. Electronic identity cards (also called eID cards) play a very important role in this regard, due to the high level of assurance they provide in identification and authentication processes. However, authentication solutions relying on them are still uncommon and suffer from many usability limitations. In this paper, we thus present the design and implementation of a novel passwordless, multi-factor authentication protocol based on eID cards. To reduce known usability issues while keeping a high level of security, our protocol leverages push notifications and mobile devices equipped with NFC, which can be used to interact with eID cards. In addition, we evaluate the security of the protocol through a formal security analysis and a risk analysis, whose results emphasize the acceptable level of security.

Over the last few years, there has been an almost exponential increase in the number of mobile applications that deal with sensitive data, such as applications for e-commerce or health. When dealing with sensitive data, classical authentication solutions based on username-password pairs are not enough, and multi-factor authentication solutions that combine two or more authentication factors of different categories are required instead. Even if several solutions are currently used, their security analyses have been performed informally or semiformally at best, and without a reference model and a precise definition of the multi-factor authentication property. This makes a comparison among the different solutions both complex and potentially misleading. In this article, we first present the design of two reference models for native applications based on the requirements of two real-world use-case scenarios. Common features between them are the use of one-time password approaches and the support of a single sign-on experience. Then, we provide a formal specification of our threat model and the security goals, and discuss the automated security analysis that we performed. Our formal analysis validates the security goals of the two reference models we propose and provides an important building block for the formal analysis of different multi-factor authentication solutions.

Cross-Site Request Forgery (CSRF) attacks are one of the critical threats to web applications. In this paper, we focus on CSRF attacks targeting web sites' authentication and identity management functionalities. We will refer to them collectively as Authentication CSRF (Auth-CSRF in short). We started by collecting several Auth-CSRF attacks reported in the literature, then analyzed their underlying strategies and identified 7 security testing strategies that can help a manual tester uncover vulnerabilities enabling Auth-CSRF. In order to check the effectiveness of our testing strategies and to estimate the incidence of Auth-CSRF, we conducted an experimental analysis considering 300 web sites belonging to 3 different rank ranges of the Alexa global top 1500. The results of our experiments are alarming: out of the 300 web sites we considered, 133 qualified for conducting our experiments and 90 of these suffered from at least one vulnerability enabling Auth-CSRF (i.e. 68%). We further generalized our testing strategies, enhanced them with the knowledge we acquired during our experiments and implemented them as an extension (namely CSRF-checker) to the open-source penetration testing tool OWASP ZAP. With the help of CSRFchecker, we tested 132 additional web sites (again from the Alexa global top 1500) and identified 95 vulnerable ones (i.e. 72%). Our findings include serious vulnerabilities among the web sites of Microsoft, Google, eBay etc. Finally, we responsibly disclosed our findings to the affected vendors.

While there exist many secure authentication and authorization solutions for web applications, their adaptation in the mobile context is a new and open challenge. In this paper, we argue that the lack of a proper reference model for Single Sign-On (SSO) for mobile native applications drives many social network vendors (acting as Identity Providers) to develop their own mobile solution. However, as the implementation details are not well documented, it is difficult to establish the proper security level of these solutions. We thus provide a rational reconstruction of the Facebook SSO flow, including a comparison with the OAuth 2.0 standard and a security analysis obtained testing the Facebook SSO reconstruction against a set of identified SSO attacks. Based on this analysis, we have modified and generalized the Facebook solution proposing a native SSO solution capable of solving the identified vulnerabilities and accommodating any Identity Provider.

The Android Security Framework controls the executions of applications through permissions which are statically granted by the user during installation. However, the definition of security policies over permissions is not supported. Security policies must be therefore manually encoded into the application by the developer, which is a dangerous practice and may cause security breaches. We propose an improvement over the Android permission system that supports the specification and enforcement of fine-grained security policies. Enforcement is achieved by reducing policy decision problems to propositional satisfiability and leveraging a state-of-the-art SAT solver. Unlike alternative proposals, our approach does not require changes in the operating system and, therefore, it can be readily deployed in any commercial device.

Business applications are more and more collaborative (cross-domains, cross-devices, service composition). Security shall focus on the overall application scenario including the interplay between its entities/devices/services, not only on the isolated systems within it. In this paper we propose the Security Threat Identification And TEsting (STIATE) toolkit to support development teams toward security assessment of their under-development applications focusing on subtle security logic flaws that may go undetected by using current industrial technology. At design-time, STIATE supports the development teams toward threat modeling and analysis by identifying automatically potential threats (via model checking and mutation techniques) on top of sequence diagrams enriched with security annotations (including WHAT-IF conditions). At run-time, STIATE supports the development teams toward testing by exploiting the identified threats to automatically generate and execute test cases on the up and running application. We demonstrate the usage of the STIATE toolkit on an application scenario employing the SAML Single Sign-On multi-party protocol, a well-known industrial security standard largely studied in previous literature.

The widespread adoption of Application Programming Interfaces (APIs) by enterprises is changing the way business is done by permitting the implementation of a multitude of apps, customized to user needs. While supporting a more flexible exploitation of available data, services and applications developed on top of APIs are vulnerable to a variety of attacks, ranging from SQL injection to unauthorized access of sensitive data. Available security solutions must be re-used and/or adapted to work with APIs. In this paper, we focus on the development of a flexible access control mechanism for APIs. This is an important security mechanism to guarantee the enforcement of authorization constraints on resources while invoking their API functions. We have developed an extension of the Spring Security framework, the standard for securing services and apps built in the popular (open source) Spring framework, for the specification and enforcement of Attribute-Based Access Control (ABAC) policies. We demonstrate our work with scenarios arising in a smart energy eco-system.

Most model checking techniques for security protocols make a number of simplifying assumptions on the protocol and/or on its execution environment that prevent their applicability in some important cases. For instance, most techniques assume that communication between honest principals is controlled by a Dolev -Yao intruder, i.e. a malicious agent capable to overhear, divert, and fake messages. Yet we might be interested in establishing the security of a protocol that relies on a less unsecure channel (e.g. a confidential channel provided by some other protocol sitting lower in the protocol stack). In this paper we propose a general model for security protocols based on the set-rewriting formalism that, coupled with the use of LTL, allows for the specification of assumptions on principals and communication channels as well as complex security properties that are normally not handled by state-of-the-art protocol analysers. By using our approach we have been able to formalise all the assumptions required by the ASW protocol for optimistic fair exchange as well as some of its security properties. Besides the previously reported attacks on the protocol, we report a new attack on a patched version of the protocol.