A network access control framework for 6LoWPAN networks

Low power over wireless personal area networks (LoWPAN), in particular wireless sensor networks, represent an emerging technology with high potential to be employed in critical situations like security surveillance, battlefields, smart-grids, and in e-health applications. The support of security services in LoWPAN is considered a challenge. First, this type of networks is usually deployed in unattended environments, making them vulnerable to security attacks. Second, the constraints inherent to LoWPAN, such as scarce resources and limited battery capacity, impose a careful planning on how and where the security services should be deployed. Besides protecting the network from some well-known threats, it is important that security mechanisms be able to withstand attacks that have not been identified before. One way of reaching this goal is to control, at the network access level, which nodes can be attached to the network and to enforce their security compliance. This paper presents a network access security framework that can be used to control the nodes that have access to the network, based on administrative approval, and to enforce security compliance to the authorized nodes

Fault-Tolerant Aggregate Signatures

Aggregate signature schemes allow for the creation of a short aggregate of multiple signatures. This feature leads to significant reductions of bandwidth and storage space in sensor networks, secure routing protocols, certificate chains, software authentication, and secure logging mechanisms. Unfortunately, in all prior schemes, adding a single invalid signature to a valid aggregate renders the whole aggregate invalid. Verifying such an invalid aggregate provides no information on the validity of any individual signature. Hence, adding a single faulty signature destroys the proof of integrity and authenticity for a possibly large amount of data. This is largely impractical in a range of scenarios, e.g. secure logging, where a single tampered log entry would render the aggregate signature of all log entries invalid. In this paper, we introduce the notion of fault-tolerant aggregate signature schemes. In such a scheme, the verification algorithm is able to determine the subset of all messages belonging to an aggregate that were signed correctly, provided that the number of aggregated faulty signatures does not exceed a certain bound. We give a generic construction of fault-tolerant aggregate signatures from ordinary aggregate signatures based on cover-free families. A signature in our scheme is a small vector of aggregated signatures of the underlying scheme. Our scheme is bounded, i.e. the number of signatures that can be aggregated into one signature must be fixed in advance. However the length of an aggregate signature is logarithmic in this number. We also present an unbounded construction, where the size of the aggregate signature grows linearly in the number of aggregated messages, but the factor in this linear function can be made arbitrarily small. The additional information encoded in our signatures can also be used to speed up verification (compared to ordinary aggregate signatures) in cases where one is only interested in verifying the validity of a single message in an aggregate, a feature beyond fault-tolerance that might be of independent interest. For concreteness, we give an instantiation using a suitable cover-free family

Fault-Tolerance and Deaggregation Security of Aggregate Signatures

Ein zentrales Problem der digitalen Kommunikation ist die Absicherung der Authentizität und Integrität digitaler Dokumente, wie etwa Webseiten, E-Mails oder Programmen. So soll beispielsweise für den Empfänger einer E-Mail nachvollziehbar sein, dass die empfangene E-Mail tatsächlich vom angegebenen Absender stammt (Authentizität) und nicht durch Dritte verändert wurde (Integrität). Digitale Signaturen sind ein Hauptwerkzeug der Kryptographie und IT-Sicherheit, um diese Eigenschaften zu gewährleisten. Hierzu wird vom Absender ein geheimer Schlüssel verwendet, um für das zu sichernde Dokument eine Signatur zu erstellen, die mithilfe eines öffentlich bekannten Verifikationsschlüssels jederzeit überprüft werden kann. Die Sicherheitseigenschaften solcher digitaler Signaturverfahren garantieren sowohl, dass jede Änderung am Dokument dazu führt, dass diese Überprüfung fehlschlägt, als auch dass eine Fälschung einer Signatur praktisch unmöglich ist, d.h. ohne den geheimen Schlüssel kann keine gültige Signatur berechnet werden. Somit kann bei einer erfolgreichen Verifikation davon ausgegangen werden, dass das Dokument tatsächlich vom angegebenen Absender erstellt und seit der Berechnung der Signatur nicht verändert wurde, da nur der Absender über den geheimen Schlüssel verfügt. Aggregierbare Signaturen bieten zusätzlich die Möglichkeit Signaturen mehrerer Dokumente zu einer einzigen Signatur zusammenzuführen bzw. zu aggregieren. Diese Aggregation ist dabei jederzeit möglich. Eine aggregierte Signatur bezeugt weiterhin sicher die Integrität und Authentizität aller ursprünglichen Dokumente, benötigt dabei aber nur so viel Speicherplatz wie eine einzelne Signatur. Außerdem ist die Verifikation einer solchen aggregierten Signatur üblichrweise schneller möglich als die sukzessive Überprüfung aller Einzelsignaturen. Somit kann die Verwendung eines aggregierbaren Signaturverfahrens anstelle eines gewöhnlichen Verfahrens zu erheblichen Verbesserungen der Performanz und des Speicherverbrauchs bei Anwendungen von Signaturen führen. In dieser Dissertation werden zwei zusätzliche Eigenschaften von aggregierbaren Signaturverfahren namens Fehlertoleranz und Deaggregationssicherheit untersucht. Fehlertoleranz bietet eine Absicherung des Verfahrens gegen fehlerhafte Signier- und Aggregationsvorgänge und Deaggregationssicherheit schützt vor ungewollten Löschungen. Beide Eigenschaften werden im Folgenden erläutert. Fehlertoleranz: Durch System- und Programmfehler, sowie inkorrektes oder auch bösartiges Nutzerverhalten ist es möglich, dass fehlerhafte Einzelsignaturen zu einer bestehenden aggregierten Signatur hinzugefügt werden. Alle bisherige aggregierbaren Signaturverfahren haben jedoch den Nachteil, dass bereits das Aggregieren einer einzigen fehlerhaften Einzelsignatur dazu führt, dass auch die aggregierte Signatur fehlerhaft und somit unbrauchbar wird. Die aggregierte Signatur kann danach nicht mehr korrekt verifiziert werden. Insbesondere kann aus ihr nun keinerlei Aussage mehr über die Integrität und Authentizität der Dokumente abgeleitet werden, die vor dem Hinzufügen der fehlerhaften Einzelsignatur korrekt signiert wurden. Dies hat zur Folge, dass alle gegebenen Sicherheitsgarantien verloren gehen und es wird ein aufwändiges Neusignieren aller Dokumente notwendig, welches unter Umständen und je nach Anwendung nur schwer bis überhaupt nicht möglich ist. In dieser Dissertation wird das erste fehlertolerante aggregierbare Signaturverfahren vorgestellt, bei dem das Hinzufügen einzelner falscher Signaturen bis zu einer gewissen Grenze keine schädlichen Auswirkungen hat. Eine aggregierte Signatur wird erst dann ungültig und unbrauchbar, sobald die Anzahl hinzugefügter fehlerhafter Signaturen diese Grenze überschreitet und behält davor weiterhin seine Gültigkeit für die korrekt signierten Dokumente. Dazu wird ein Verfahren vorgestellt, mit dem jedes beliebige aggregierbare Signaturverfahren in ein fehlertolerantes Verfahren transformiert werden kann. Das zugrundeliegende Verfahren wird dabei nur als Black-Box verwendet und der Schutz gegen Fälschungsangriffe übertragt sich beweisbar und ohne Einschränkung auf das neue fehlertolerante Verfahren. Des Weiteren wird als Anwendung von fehlertoleranten Verfahren gezeigt, wie aus ihnen ein sicheres Log-Verfahren konstruiert werden kann. Deaggregationssicherheit: Erlangt ein Angreifer Zugriff auf eine aggregierte Signatur für einen bestimmten Datensatz, so sollte es ihm nicht möglich sein aus diesem Aggregat eine gültige Signatur für einen Teil der geschützten Dokumente abzuleiten, indem er einzelne Signaturen entfernt oder deaggregiert. Solche Angriffe können für viele Anwendungsfälle problematisch sein, da so Signaturen für Mengen von Dokumenten berechnet werden könnten, die nicht von den eigentlichen Erstellern beabsichtigt waren und nie von ihnen selbst signiert wurden. Wird ein aggregierbares Signaturverfahren etwa verwendet um eine Datenbank abzusichern, so sollte es Angreifern nicht möglich sein einzelne Einträge daraus zu entfernen. In dieser Dissertation werden mehrere Deaggregationssicherheitsbegriffe entwickelt, vorgestellt und untersucht. Dazu wird eine Hierarchie von verschieden starken Sicherheitsbegriffen entwickelt und die Zusammenhänge zwischen den einzelnen Begriffen werden formal untersucht. Dabei wird auch gezeigt, dass der von aggregierbaren Signaturverfahren garantierte Schutz gegen Fälschungen keinerlei Sicherheit gegen Deaggregationsangriffe gewährleistet. Des Weiteren wird die Deaggregationssicherheit einer Reihe von bekannten und wichtigen aggregierbaren Signaturverfahren näher betrachtet. Die von diesen Verfahren gebotene Sicherheit wird exakt klassifiziert, indem entweder Angriffsmöglichkeiten demonstriert werden oder formal bewiesen wird, welcher Sicherheitsbegriff der Hierarchie vom Verfahren erfüllt wird. Außerdem wird die Verbindung von Fehlertoleranz und Deaggregationssicherheit untersucht. Dabei stellt sich heraus, dass beide Begriffe nicht zueinander kompatibel sind, indem bewiesen wird, dass fehlertolerante aggregierbare Signaturverfahren keinerlei Sicherheit gegen Deaggregationsangriffe bieten können. Somit muss bei Anwendungen von aggregierbaren Verfahren genau abgewogen werden, welche der beiden Eigenschaften notwendig ist und ob zusätzliche Sicherheitsmaßnahmen angewendet werden müssen, um dieses Problem für die konkrete Anwendung zu beheben

Optimized protection of streaming media authenticity

Ph.DDOCTOR OF PHILOSOPH

Active and passive approaches for image authentication

Ph.DDOCTOR OF PHILOSOPH

Blockchain in maritime cybersecurity

Blockchain technologies can be used for many different purposes from handling large amounts of data to creating better solutions for privacy protection, user authentication and a tamper proof ledger which lead to growing interest among industries. Smart contracts, fog nodes and different consensus methods create a scalable environment to secure multi-party connections with equal trust of participanting nodes’ identity. Different blockchains have multiple options for methodologies to use in different environments. This thesis has focused on Ethereum based open-source solutions that fit the remote pilotage environment the best. Autonomous vehicular networks and remote operatable devices have been a popular research topic in the last few years. Remote pilotage in maritime environment is persumed to reach its full potential with fully autonomous vessels in ten years which makes the topic interesting for all researchers. However cybersecurity in these environments is especially important because incidents can lead to financial loss, reputational damage, loss of customer and industry trust and environmental damage. These complex environments also have multiple attack vectors because of the systems wireless nature. Denial-of-service (DoS), man-in-the-middle (MITM), message or executable code injection, authentication tampering and GPS spoofing are one of the most usual attacks against large IoT systems. This is why blockchain can be used for creating a tamper proof environment with no single point-of-failure. After extensive research about best performing blockchain technologies Ethereum seemed the most preferable for decentralised maritime environment. In comparison to most of 2021 blockchain technologies that have focused on financial industries and cryptocurrencies, Ethereum has focused on decentralizing applications within many different industries. This thesis provides three Ethereum based blockchain protocol solutions and one operating system for these protocols. All have different features that add to the base blockchain technology but after extensive comparison two of these protocols perform better in means of concurrency and privacy. Hyperledger Fabric and Quorum provide many ways of tackling privacy, concurrency and parallel execution issues with consistent high throughput levels. However Hyperledger Fabric has far better throughput and concurrency management. This makes the solution of Firefly operating system with Hyperledger Fabric blockchain protocol the most preferable solution in complex remote pilotage fairway environment

Advanced Cryptographic Techniques for Protecting Log Data

This thesis examines cryptographic techniques providing security for computer log files. It focuses on ensuring authenticity and integrity, i.e. the properties of having been created by a specific entity and being unmodified. Confidentiality, the property of being unknown to unauthorized entities, will be considered, too, but with less emphasis. Computer log files are recordings of actions performed and events encountered in computer systems. While the complexity of computer systems is steadily growing, it is increasingly difficult to predict how a given system will behave under certain conditions, or to retrospectively reconstruct and explain which events and conditions led to a specific behavior. Computer log files help to mitigate the problem of retracing a system’s behavior retrospectively by providing a (usually chronological) view of events and actions encountered in a system. Authenticity and integrity of computer log files are widely recognized security requirements, see e.g. [Latham, ed., "Department of Defense Trusted Computer System Evaluation Criteria", 1985, p. 10], [Kent and Souppaya, "Guide to Computer Security Log Management", NIST Special Publication 800-92, 2006, Section 2.3.2], [Guttman and Roback, "An Introduction to Computer Security: The NIST Handbook", superseded NIST Special Publication 800-12, 1995, Section 18.3.1], [Nieles et al., "An Introduction to Information Security" , NIST Special Publication 800-12, 2017, Section 9.3], [Common Criteria Editorial Board, ed., "Common Criteria for Information Technology Security Evaluation", Part 2, Section 8.6]. Two commonly cited ways to ensure integrity of log files are to store log data on so-called write-once-read-many-times (WORM) drives and to immediately print log records on a continuous-feed printer. This guarantees that log data cannot be retroactively modified by an attacker without physical access to the storage medium. However, such special-purpose hardware may not always be a viable option for the application at hand, for example because it may be too costly. In such cases, the integrity and authenticity of log records must be ensured via other means, e.g. with cryptographic techniques. Although these techniques cannot prevent the modification of log data, they can offer strong guarantees that modifications will be detectable, while being implementable in software. Furthermore, cryptography can be used to achieve public verifiability of log files, which may be needed in applications that have strong transparency requirements. Cryptographic techniques can even be used in addition to hardware solutions, providing protection against attackers who do have physical access to the logging hardware, such as insiders. Cryptographic schemes for protecting stored log data need to be resilient against attackers who obtain control over the computer storing the log data. If this computer operates in a standalone fashion, it is an absolute requirement for the cryptographic schemes to offer security even in the event of a key compromise. As this is impossible with standard cryptographic tools, cryptographic solutions for protecting log data typically make use of forward-secure schemes, guaranteeing that changes to log data recorded in the past can be detected. Such schemes use a sequence of authentication keys instead of a single one, where previous keys cannot be computed efficiently from latter ones. This thesis considers the following requirements for, and desirable features of, cryptographic logging schemes: 1) security, i.e. the ability to reliably detect violations of integrity and authenticity, including detection of log truncations, 2) efficiency regarding both computational and storage overhead, 3) robustness, i.e. the ability to verify unmodified log entries even if others have been illicitly changed, and 4) verifiability of excerpts, including checking an excerpt for omissions. The goals of this thesis are to devise new techniques for the construction of cryptographic schemes that provide security for computer log files, to give concrete constructions of such schemes, to develop new models that can accurately capture the security guarantees offered by the new schemes, as well as to examine the security of previously published schemes. This thesis demands that cryptographic schemes for securely storing log data must be able to detect if log entries have been deleted from a log file. A special case of deletion is log truncation, where a continuous subsequence of log records from the end of the log file is deleted. Obtaining truncation resistance, i.e. the ability to detect truncations, is one of the major difficulties when designing cryptographic logging schemes. This thesis alleviates this problem by introducing a novel technique to detect log truncations without the help of third parties or designated logging hardware. Moreover, this work presents new formal security notions capturing truncation resistance. The technique mentioned above is applied to obtain cryptographic logging schemes which can be shown to satisfy these notions under mild assumptions, making them the first schemes with formally proven truncation security. Furthermore, this thesis develops a cryptographic scheme for the protection of log files which can support the creation of excerpts. For this thesis, an excerpt is a (not necessarily contiguous) subsequence of records from a log file. Excerpts created with the scheme presented in this thesis can be publicly checked for integrity and authenticity (as explained above) as well as for completeness, i.e. the property that no relevant log entry has been omitted from the excerpt. Excerpts provide a natural way to preserve the confidentiality of information that is contained in a log file, but not of interest for a specific public analysis of the log file, enabling the owner of the log file to meet confidentiality and transparency requirements at the same time. The scheme demonstrates and exemplifies the technique for obtaining truncation security mentioned above. Since cryptographic techniques to safeguard log files usually require authenticating log entries individually, some researchers [Ma and Tsudik, "A New Approach to Secure Logging", LNCS 5094, 2008; Ma and Tsudik, "A New Approach to Secure Logging", ACM TOS 2009; Yavuz and Peng, "BAF: An Efficient Publicly Verifiable Secure Audit Logging Scheme for Distributed Systems", ACSAC 2009] have proposed using aggregatable signatures [Boneh et al., "Aggregate and Verifiably Encrypted Signatures from Bilinear Maps", EUROCRYPT 2003] in order to reduce the overhead in storage space incurred by using such a cryptographic scheme. Aggregation of signatures refers to some “combination” of any number of signatures (for distinct or equal messages, by distinct or identical signers) into an “aggregate” signature. The size of the aggregate signature should be less than the total of the sizes of the orginal signatures, ideally the size of one of the original signatures. Using aggregation of signatures in applications that require storing or transmitting a large number of signatures (such as the storage of log records) can lead to significant reductions in the use of storage space and bandwidth. However, aggregating the signatures for all log records into a single signature will cause some fragility: The modification of a single log entry will render the aggregate signature invalid, preventing the cryptographic verification of any part of the log file. However, being able to distinguish manipulated log entries from non-manipulated ones may be of importance for after-the-fact investigations. This thesis addresses this issue by presenting a new technique providing a trade-off between storage overhead and robustness, i.e. the ability to tolerate some modifications to the log file while preserving the cryptographic verifiability of unmodified log entries. This robustness is achieved by the use of a special kind of aggregate signatures (called fault-tolerant aggregate signatures), which contain some redundancy. The construction makes use of combinatorial methods guaranteeing that if the number of errors is below a certain threshold, then there will be enough redundancy to identify and verify the non-modified log entries. Finally, this thesis presents a total of four attacks on three different schemes intended for securely storing log files presented in the literature [Yavuz et al., "Efficient, Compromise Resilient and Append-Only Cryptographic Schemes for Secure Audit Logging", Financial Cryptography 2012; Ma, "Practical Forward Secure Sequential Aggregate Signatures", ASIACCS 2008]. The attacks allow for virtually arbitrary log file forgeries or even recovery of the secret key used for authenticating the log file, which could then be used for mostly arbitrary log file forgeries, too. All of these attacks exploit weaknesses of the specific schemes. Three of the attacks presented here contradict the security properties of the schemes claimed and supposedly proven by the respective authors. This thesis briefly discusses these proofs and points out their flaws. The fourth attack presented here is outside of the security model considered by the scheme’s authors, but nonetheless presents a realistic threat. In summary, this thesis advances the scientific state-of-the-art with regard to providing security for computer log files in a number of ways: by introducing a new technique for obtaining security against log truncations, by providing the first scheme where excerpts from log files can be verified for completeness, by describing the first scheme that can achieve some notion of robustness while being able to aggregate log record signatures, and by analyzing the security of previously proposed schemes

A Survey on Wireless Sensor Network Security

Wireless sensor networks (WSNs) have recently attracted a lot of interest in the research community due their wide range of applications. Due to distributed nature of these networks and their deployment in remote areas, these networks are vulnerable to numerous security threats that can adversely affect their proper functioning. This problem is more critical if the network is deployed for some mission-critical applications such as in a tactical battlefield. Random failure of nodes is also very likely in real-life deployment scenarios. Due to resource constraints in the sensor nodes, traditional security mechanisms with large overhead of computation and communication are infeasible in WSNs. Security in sensor networks is, therefore, a particularly challenging task. This paper discusses the current state of the art in security mechanisms for WSNs. Various types of attacks are discussed and their countermeasures presented. A brief discussion on the future direction of research in WSN security is also included.Comment: 24 pages, 4 figures, 2 table