Security Ceremonies Research Articles

A mutation-based approach for the formal and automated analysis of security ceremonies

There is an increasing number of cyber-systems (e.g., systems for payment, transportation, voting, critical infrastructures) whose security depends intrinsically on human users. In this paper, we introduce a novel approach for the formal and automated analysis of security ceremonies. A security ceremony expands a security protocol to include human nodes alongside computer nodes, with communication links that comprise user interfaces, human-to-human communication and transfers of physical objects that carry data, and thus a ceremony’s security analysis should include, in particular, the mistakes that human users might make when participating actively in the ceremony. Our approach defines mutation rules that model possible behaviors of a human user, automatically generates mutations in the behavior of the other agents of the ceremony to match the human-induced mutations, and automatically propagates these mutations through the whole ceremony. This allows for the analysis of the original ceremony specification and its possible mutations, which may include the way in which the ceremony has actually been implemented or could be implemented. To automate our approach, we have developed the tool X-Men, which is a prototype that builds on top of Tamarin, one of the most common tools for the automatic unbounded verification of security protocols. As a proof of concept, we have applied our approach to three real-life case studies, uncovering a number of concrete vulnerabilities. Some of these vulnerabilities were so far unknown, whereas others had so far been discovered only by empirical observation of the actual ceremony execution or by directly formalizing alternative models of the ceremony by hand, but X-Men instead allowed us to find them automatically.

Perceptions of Beauty in Security Ceremonies

When we use secure computer systems, we engage with carefully orchestrated and ordered interactions called “security ceremonies”, all of which exist to assure security. A great deal of attention has been paid to improving the usability of these ceremonies over the last two decades, to make them easier for end-users to engage with. Yet, usability improvements do not seem to have endeared end users to ceremonies. As a consequence, human actors might subvert the ceremony’s processes or avoid engaging with it. Here, we consider whether beautification could be one way of making ceremonies more appealing. To explore beautification in this context, we carried out three studies. Study 1 surveyed 250 participants to derive a wide range of potential dimensions of “beautiful ceremonies”. These statements were sorted into dominant themes and converted into statements, which fed into the second study, with 309 respondents, to reveal the dominant dimensions constituting beauty. Study 3 asked 41 participants to carry out a Q-sort, which revealed the ways that people combine the identified dimensions when characterising security ceremonies as “beautiful”. These studies have allowed us to pin down the perceived dimensions of beauty in the context of security ceremonies, and also to understand how people combine these dimensions in different ways in judging security ceremonies to be beautiful, confirming the old adage of beauty being “in the eye of the beholder”. We conclude by highlighting the constraints imposed by the overarching requirement for security to be maintained in the face of any usability improvements and beautification endeavours.

Modelling human threats in security ceremonies1

Socio-Technical Systems (STSs) combine the operations of technical systems with the choices and intervention of humans, namely the users of the technical systems. Designing such systems is far from trivial due to the interaction of heterogeneous components, including hardware components and software applications, physical elements such as tickets, user interfaces, such as touchscreens and displays, and notably, humans. While the possible security issues about the technical components are well known yet continuously investigated, the focus of this article is on the various levels of threat that human actors may pose, namely, the focus is on security ceremonies. The approach is to formally model human threats systematically and to formally verify whether they can break the security properties of a few running examples: two currently deployed Deposit-Return Systems (DRSs) and a variant that we designed to strengthen them. The two real-world DRSs are found to support security properties differently, and some relevant properties fail, yet our variant is verified to meet all the properties. Our human threat model is distributed and interacting: it formalises all humans as potential threatening users because they can execute rules that encode specific threats in addition to being honest, that is, to follow the prescribed rules of interaction with the technical system; additionally, humans may exchange information or objects directly, hence practically favour each other although no specific form of collusion is prescribed. We start by introducing four different human threat models, and some security properties are found to succumb against the strongest model, the addition of the four. The question then arises on what meaningful combinations of the four would not break the properties. This leads to the definition of a lattice of human threat models and to a general methodology to traverse it by verifying each node against the properties. The methodology is executed on our running example for the sake of demonstration. Our approach thus is modular and extensible to include additional threats, potentially even borrowed from existing works, and, consequently, to the growth of the corresponding lattice. STSs can easily become very complex, hence we deem modularity and extensibility of the human threat model as key factors. The current computer-assisted tool support is put to test but proves to be sufficient.

Formalizing and analyzing security ceremonies with heterogeneous devices in ANP and PDL

In today's security protocols (also called “security ceremonies” when humans play a key role), different nodes may have different capabilities: computers can encrypt and decrypt messages, whereas humans cannot; a biometric device can capture biometric information, whereas a random number generator used in e-banking cannot; and so on. Furthermore, even if a node has the decryption capability, it must also know the encryption key to decrypt a message. Actor-network procedures (ANPs) are a well-known formal model of heterogeneous security protocols by Meadows and Pavlovic, and their procedure derivation logic (PDL) supports the logical reasoning about ANPs. However, ANPs do not support explicitly specifying node capabilities, and PDL does not support reasoning explicitly about the knowledge of the participants at different points in time. In this paper, we extend ANPs to deal with heterogeneous devices by explicitly specifying the nodes' capabilities, as well as by adding new types of events. We also modify PDL to take into account the knowledge of participants at different points in time, and extend PDL to reason both from a “bird's-eye” view of the system, as well from a “node's-eye” view. All this allows us to reason about secrecy and authentication in security protocols/ceremonies with different kinds of devices and human users. We illustrate the use of our modeling notation ANP-C and our logics PDL-CK and PDL-CKL to specify and reason about a number of scenarios involving different kinds of devices, including: scenarios for updating someone's data in a smart card reader; an SSL/TLS ceremony involving a user, a smartphone with a fingerprint reader, and a remote computer/server; and scenarios involving the YubiKey authentication device used by companies such as Google, Facebook, and Bank of America.

Out to explore the cybersecurity planet

PurposeSecurity ceremonies still fail despite decades of efforts by researchers and practitioners. Attacks are often a cunning amalgam of exploits for technical systems and of forms of human behaviour. For example, this is the case with the recent news headline of a large-scale attack against Electrum Bitcoin wallets, which manages to spread a malicious update of the wallet app. The author therefore sets out to look at things through a different lens.Design/methodology/approachThe author makes the (metaphorical) hypothesis that humans arrived on Earth along with security ceremonies from a very far planet, the Cybersecurity planet. The author’s hypothesis continues, in that studying (by huge telescopes) the surface of Cybersecurity in combination with the logical projection on that surface of what happens on Earth is beneficial for us earthlings.FindingsThe author has spotted four cities so far on the remote planet. Democratic City features security ceremonies that allow humans to follow personal paths of practice and, for example, make errors or be driven by emotions. By contrast, security ceremonies in Dictatorial City compel to comply, hence humans here behave like programmed automata. Security ceremonies in Beautiful City are so beautiful that humans just love to follow them precisely. Invisible City has security ceremonies that are not perceivable, hence humans feel like they never encounter any. Incidentally, the words “democratic” and “dictatorial” are used without any political connotation.Originality/valueA key argument the author shall develop is that all cities but Democratic City address the human factor, albeit in different ways. In the light of these findings, the author will also discuss security ceremonies of our planet, such as WhatsApp Web login and flight boarding, and explore room for improving them based upon the current understanding of Cybersecurity.

An adaptive threat model for security ceremonies

Ever since Needham and Schroeder introduced the notion of an active attacker, significant research has been conducted regarding protocol design and analysis to verify that the protocols' goals are robust against this type of attacker. Nowadays, the Dolev---Yao threat model is the most widely accepted attacker model for the analysis of security protocols. Consequently, there are several security protocols considered secure against an attacker under Dolev---Yao's assumptions. With the introduction of the concept of ceremonies, which extends protocol design and analysis to include human peers, we can potentially find and solve security flaws that were previously not detectable. In this paper, we discuss that even though Dolev---Yao's threat model can represent the most powerful attacker possible in a ceremony, the attacker in this model is not realistic in certain scenarios, especially those related to human peers. We propose a dynamic threat model that can be adjusted according to each ceremony and consequently adapt the model and the ceremony analysis to realistic scenarios. We demonstrate the feasibility of our approach with a support implementation using first-order logic and an automatic theorem prover.

Actor Network Procedures as Psi-calculi for Security Ceremonies

The actor network procedures of Pavlovic and Meadows are a recent graphical formalism developed for describing security ceremonies and for reasoning about their security properties. The present work studies the relations of the actor network procedures (ANP) to the recent psi-calculi framework. Psi-calculi is a parametric formalism where calculi like spi- or applied-pi are found as instances. Psi-calculi are operational and largely non-graphical, but have strong foundation based on the theory of nominal sets and process algebras. One purpose of the present work is to give a semantics to ANP through psi-calculi. Another aim was to give a graphical language for a psi-calculus instance for security ceremonies. At the same time, this work provides more insight into the details of the ANPs formalization and the graphical representation.