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Towards a Formal Verification of Seamless Cryptographic Rekeying in Real-Time Communication Systems
(2022)
This paper makes two contributions to the verification of communication protocols by transition systems. Firstly, the paper presents a modeling of a cyclic communication protocol using a synchronized network of transition systems. This protocol enables seamless cryptographic rekeying embedded into cyclic messages. Secondly, we test the protocol using the model checking verification technique.
It seems to be a widespread impression that the use of strong cryptography inevitably imposes a prohibitive burden on industrial communication systems, at least inasmuch as real-time requirements in cyclic fieldbus communications are concerned. AES-GCM is a leading cryptographic algorithm for authenticated encryption, which protects data against disclosure and manipulations. We study the use of both hardware and software-based implementations of AES-GCM. By simulations as well as measurements on an FPGA-based prototype setup we gain and substantiate an important insight: for devices with a 100 Mbps full-duplex link, a single low-footprint AES-GCM hardware engine can deterministically cope with the worst-case computational load, i.e., even if the device maintains a maximum number of cyclic communication relations with individual cryptographic keys. Our results show that hardware support for AES-GCM in industrial fieldbus components may actually be very lightweight.
Cryptographic protection of messages requires frequent updates of the symmetric cipher key used for encryption and decryption, respectively. Protocols of legacy IT security, like TLS, SSH, or MACsec implement rekeying under the assumption that, first, application data exchange is allowed to stall occasionally and, second, dedicated control messages to orchestrate the process can be exchanged. In real-time automation applications, the first is generally prohibitive, while the second may induce problematic traffic patterns on the network. We present a novel seamless rekeying approach, which can be embedded into cyclic application data exchanges. Although, being agnostic to the underlying real-time communication system, we developed a demonstrator emulating the widespread industrial Ethernet system PROFINET IO and successfully use this rekeying mechanism.
With the increasing degree of interconnectivity in industrial factories, security becomes more and more the most important stepping-stone towards wide adoption of the Industrial Internet of Things (IIoT). This paper summarizes the most important aspects of one keynote of DESSERT2020 conference. It highlights the ongoing and open research activities on the different levels, from novel cryptographic algorithms over security protocol integration and testing to security architectures for the full lifetime of devices and systems. It includes an overview of the research activities at the authors' institute.
Die industrielle Kommunikation war früher von relativ eingeschränkten, geschlossenen Feldbussystemen geprägt. Mit der zunehmenden Öffnung von Automatisierungsnetzen durch die horizontale und vertikale Integration in Produktionsanlagen entstehen gefährliche Angriffsflächen, die zum Diebstahl von Produktionsgeheimnissen, der Manipulation oder dem kompletten Lahmlegen der Produktionsprozesse führen können. Hieraus ergeben sich grundlegend neue Anforderung an die Datensicherheit, denen mit innovativen Lösungsansätzen begegnet werden muss.
Ziel des Forschungsvorhabens „SecureField“ war es, die Umsetzbarkeit und Anwendbarkeit des Ansatzes „(D)TLS-over-Anything“ zu untersuchen und nachzuweisen, sowie einen Werkzeugkasten zur Definition und Implementierung entsprechender Sicherheitslösungen vorzubereiten. Als langjährig etablierter Standard im IT-Umfeld stellte sich das (Datagram) Transport Layer Security ((D)TLS) Protokoll in Kombination mit einer industrie- bzw. automatisierungskompatiblen Public-Key-Infrastruktur (PKI) als äußerst vielversprechende Möglichkeit dar, Datensicherheit auch im OT-Umfeld zu erzielen. Hierbei sollten insbesondere KMU adressiert werden, für welche eigene Entwicklungsarbeiten in diesem Umfeld häufig zu aufwändig und technisch sowie wirtschaftlich zu riskant sind.
Mit „SecureField“ konnten Ergebnisse auf mehreren Ebenen erzielt werden. Zunächst konnte im Projektverlauf ein umfassendes und generisches Konzept zur Ende-zu-Ende-Absicherung von Kommunikationspfaden und -protokollen im industriellen Umfeld erarbeitet werden. Dieses Konzept besteht aus einem generischen Kommunikationsmodell sowie aus einem generischen Authentifikationsmodell.
Real-Time Ethernet has become the major communication technology for modern automation and industrial control systems. On the one hand, this trend increases the need for an automation-friendly security solution, as such networks can no longer be considered sufficiently isolated. On the other hand, it shows that, despite diverging requirements, the domain of Operational Technology (OT) can derive advantage from high-volume technology of the Information Technology (IT) domain. Based on these two sides of the same coin, we study the challenges and prospects of approaches to communication security in real-time Ethernet automation systems. In order to capitalize the expertise aggregated in decades of research and development, we put a special focus on the reuse of well-established security technology from the IT domain. We argue that enhancing such technology to become automation-friendly is likely to result in more robust and secure designs than greenfield designs. Because of its widespread deployment and the (to this date) nonexistence of a consistent security architecture, we use PROFINET as a showcase of our considerations. Security requirements for this technology are defined and different well-known solutions are examined according their suitability for PROFINET. Based on these findings, we elaborate the necessary adaptions for the deployment on PROFINET.
The Transport Layer Security (TLS) protocol is a cornerstone of secure network communication, not only for online banking, e-commerce, and social media, but also for industrial communication and cyber-physical systems. Unfortunately, implementing TLS correctly is very challenging, as becomes evident by considering the high frequency of bugfixes filed for many TLS implementations. Given the high significance of TLS, advancing the quality of implementations is a sustained pursuit. We strive to support these efforts by presenting a novel, response-distribution guided fuzzing algorithm for differential testing of black-box TLS implementations. Our algorithm generates highly diverse and mostly-valid TLS stimulation messages, which evoke more behavioral discrepancies in TLS server implementations than other algorithms. We evaluate our algorithm using 37 different TLS implementations and discuss―by means of a case study―how the resulting data allows to assess and improve not only implementations of TLS but also to identify underspecified corner cases. We introduce suspiciousness as a per-implementation metric of anomalous implementation behavior and find that more recent or bug-fixed implementations tend to have a lower suspiciousness score. Our contribution is complementary to existing tools and approaches in the area, and can help reveal implementation flaws and avoid regression. While being presented for TLS, we expect our algorithm's guidance scheme to be applicable and useful also in other contexts. Source code and data is made available for fellow researchers in order to stimulate discussions and invite others to benefit from and advance our work.
The Datagram Transport Layer Security (DTLS) protocol has been designed to provide end-to-end security over unreliable communication links. Where its connection establishment is concerned, DTLS copes with potential loss of protocol messages by implementing its own loss detection and retransmission scheme. However, the default scheme turns out to be suboptimal for links with high transmission error rates and low data rates, such as wireless links in electromagnetically harsh industrial environments. Therefore, in this paper, as a first step we provide an analysis of the standard DTLS handshake's performance under such adverse transmission conditions. Our studies are based on simulations that model message loss as the result of bit transmission errors. We consider several handshake variants, including endpoint authentication via pre-shared keys or certificates. As a second step, we propose and evaluate modifications to the way message loss is dealt with during the handshake, making DTLS deployable in situations which are prohibitive for default DTLS.
Exploiting Dissent: Towards Fuzzing-based Differential Black Box Testing of TLS Implementations
(2017)
The Transport Layer Security (TLS) protocol is one of the most widely used security protocols on the internet. Yet do implementations of TLS keep on suffering from bugs and security vulnerabilities. In large part is this due to the protocol's complexity which makes implementing and testing TLS notoriously difficult. In this paper, we present our work on using differential testing as effective means to detect issues in black-box implementations of the TLS handshake protocol. We introduce a novel fuzzing algorithm for generating large and diverse corpuses of mostly-valid TLS handshake messages. Stimulating TLS servers when expecting a ClientHello message, we find messages generated with our algorithm to induce more response discrepancies and to achieve a higher code coverage than those generated with American Fuzzy Lop, TLS-Attacker, or NEZHA. In particular, we apply our approach to OpenssL, BoringSSL, WolfSSL, mbedTLS, and MatrixSSL, and find several real implementation bugs; among them a serious vulnerability in MatrixSSL 3.8.4. Besides do our findings point to imprecision in the TLS specification. We see our approach as present in this paper as the first step towards fully interactive differential testing of black-box TLS protocol implementations. Our software tools are publicly available as open source projects.
eTPL: An Enhanced Version of the TLS Presentation Language Suitable for Automated Parser Generation
(2017)
The specification of the Transport Layer Security (TLS) protocol defines its own presentation language used for the purpose of semi-formally describing the structure and on-the-wire format of TLS protocol messages. This TLS Presentation Language (TPL) is more expressive and concise than natural language or tabular descriptions, but as a result of its limited objective has a number of deficiencies. We present eTPL, an enhanced version of TPL that improves its expressiveness, flexibility, and applicability to non-TLS scenarios. We first define a generic model that describes the parsing of binary data. Based on this, we propose language constructs for TPL that capture important information which would otherwise have to be picked manually from informal protocol descriptions. Finally, we briefly introduce our software tool etpl-tool which reads eTPL definitions and automatically generates corresponding message parsers in C++. We see our work as a contribution supporting sniffing, debugging, and rapid-prototyping of wired and wireless communication systems.
Die Vielfalt der Protokolle, die praktisch auf allen Ebenen der Netzwerkkommunikation zu berücksichtigen ist, stellt eine der großen Herausforderungen bei der fortschreitenden Automatisierung des intelligenten Hauses dar. Unter dem Überbegriff Internet der Dinge (Internet of Things) entstehen gegenwärtig zahlreiche neue Entwicklungen, Standards, Allianzen und so genannte Ökosysteme. Diese haben die Absicht einer horizontalen Integration gewerkeübergreifender Anwendungen und verfolgen fast alle das Ziel, die Situation zu vereinfachen, die Entwicklungen zu beschleunigen und Markterfolge zu erreichen. Leider macht diese Vielfalt momentan die Welt aber eher noch komplexer und bringt damit das Risiko mit sich, genau das Gegenteil der ursprünglichen Absichten zu erreichen. Dieser Beitrag versucht, die Entwicklungen möglichst systematisch zu kategorisieren und mögliche Lösungsansätze zu beschreiben.