177 research outputs found

    Denial-of-Service Resistance in Key Establishment

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    Denial of Service (DoS) attacks are an increasing problem for network connected systems. Key establishment protocols are applications that are particularly vulnerable to DoS attack as they are typically required to perform computationally expensive cryptographic operations in order to authenticate the protocol initiator and to generate the cryptographic keying material that will subsequently be used to secure the communications between initiator and responder. The goal of DoS resistance in key establishment protocols is to ensure that attackers cannot prevent a legitimate initiator and responder deriving cryptographic keys without expending resources beyond a responder-determined threshold. In this work we review the strategies and techniques used to improve resistance to DoS attacks. Three key establishment protocols implementing DoS resistance techniques are critically reviewed and the impact of misapplication of the techniques on DoS resistance is discussed. Recommendations on effectively applying resistance techniques to key establishment protocols are made

    Cryptanalysis of Server-Aided RSA Protocols with Private-Key Splitting

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    International audienceWe analyze the security and the efficiency of interactive protocols where a client wants to delegate the computation of an RSA signature given a public key, a public message and the secret signing exponent. We consider several protocols where the secret exponent is splitted using some algebraic decomposition. We first provide an exhaustive analysis of the delegation protocols in which the client outsources a single RSA exponentiation to the server. We then revisit the security of the protocols RSA-S1 and RSA-S2 that were proposed by Matsumoto, Kato and Imai in 1988. We present an improved lattice-based attack on RSA-S1 and we propose a simple variant of this protocol that provides better efficiency for the same security level. Eventually, we present the first attacks on the protocol RSA-S2 that employs the Chinese Remainder Theorem to speed up the client's computation. The efficiency of our (heuristic) attacks has been validated experimentally

    Vulnerabililty Analysis of Multi-Factor Authentication Protocols

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    In this thesis, the author hypothesizes that the use of computationally intensive mathematical operations in password authentication protocols can lead to security vulnerabilities in those protocols. In order to test this hypothesis: 1. A generalized algorithm for cryptanalysis was formulated to perform a clogging attack (a formof denial of service) on protocols that use computationally intensive modular exponentiation to guarantee security. 2. This technique was then applied to cryptanalyze four recent password authentication protocols, to determine their susceptibility to the clogging attack. The protocols analyzed in this thesis differ in their usage of factors (smart cards, memory drives, etc.) or their method of communication (encryption, nonces, timestamps, etc.). Their similarity lies in their use of computationally intensivemodular exponentiation as amediumof authentication. It is concluded that the strengths of all the protocols studied in this thesis can be combined tomake each of the protocols secure from the clogging attack. The conclusion is supported by designing countermeasures for each protocol against the clogging attack

    Privacy Preserving Cryptographic Protocols for Secure Heterogeneous Networks

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    DisertačnĂ­ prĂĄce se zabĂœvĂĄ kryptografickĂœmi protokoly poskytujĂ­cĂ­ ochranu soukromĂ­, kterĂ© jsou určeny pro zabezpečenĂ­ komunikačnĂ­ch a informačnĂ­ch systĂ©mĆŻ tvoƙícĂ­ch heterogennĂ­ sĂ­tě. PrĂĄce se zaměƙuje pƙedevĆĄĂ­m na moĆŸnosti vyuĆŸitĂ­ nekonvenčnĂ­ch kryptografickĂœch prostƙedkĆŻ, kterĂ© poskytujĂ­ rozơíƙenĂ© bezpečnostnĂ­ poĆŸadavky, jako je napƙíklad ochrana soukromĂ­ uĆŸivatelĆŻ komunikačnĂ­ho systĂ©mu. V prĂĄci je stanovena vĂœpočetnĂ­ nĂĄročnost kryptografickĂœch a matematickĂœch primitiv na rĆŻznĂœch zaƙízenĂ­ch, kterĂ© se podĂ­lĂ­ na zabezpečenĂ­ heterogennĂ­ sĂ­tě. HlavnĂ­ cĂ­le prĂĄce se zaměƙujĂ­ na nĂĄvrh pokročilĂœch kryptografickĂœch protokolĆŻ poskytujĂ­cĂ­ch ochranu soukromĂ­. V prĂĄci jsou navrĆŸeny celkově tƙi protokoly, kterĂ© vyuĆŸĂ­vajĂ­ skupinovĂœch podpisĆŻ zaloĆŸenĂœch na bilineĂĄrnĂ­m pĂĄrovĂĄnĂ­ pro zajiĆĄtěnĂ­ ochrany soukromĂ­ uĆŸivatelĆŻ. Tyto navrĆŸenĂ© protokoly zajiĆĄĆ„ujĂ­ ochranu soukromĂ­ a nepopiratelnost po celou dobu datovĂ© komunikace spolu s autentizacĂ­ a integritou pƙenĂĄĆĄenĂœch zprĂĄv. Pro navĂœĆĄenĂ­ vĂœkonnosti navrĆŸenĂœch protokolĆŻ je vyuĆŸito optimalizačnĂ­ch technik, napƙ. dĂĄvkovĂ©ho ověƙovĂĄnĂ­, tak aby protokoly byly praktickĂ© i pro heterogennĂ­ sĂ­tě.The dissertation thesis deals with privacy-preserving cryptographic protocols for secure communication and information systems forming heterogeneous networks. The thesis focuses on the possibilities of using non-conventional cryptographic primitives that provide enhanced security features, such as the protection of user privacy in communication systems. In the dissertation, the performance of cryptographic and mathematic primitives on various devices that participate in the security of heterogeneous networks is evaluated. The main objectives of the thesis focus on the design of advanced privacy-preserving cryptographic protocols. There are three designed protocols which use pairing-based group signatures to ensure user privacy. These proposals ensure the protection of user privacy together with the authentication, integrity and non-repudiation of transmitted messages during communication. The protocols employ the optimization techniques such as batch verification to increase their performance and become more practical in heterogeneous networks.

    Secure data sharing in cloud and IoT by leveraging attribute-based encryption and blockchain

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    “Data sharing is very important to enable different types of cloud and IoT-based services. For example, organizations migrate their data to the cloud and share it with employees and customers in order to enjoy better fault-tolerance, high-availability, and scalability offered by the cloud. Wearable devices such as smart watch share user’s activity, location, and health data (e.g., heart rate, ECG) with the service provider for smart analytic. However, data can be sensitive, and the cloud and IoT service providers cannot be fully trusted with maintaining the security, privacy, and confidentiality of the data. Hence, new schemes and protocols are required to enable secure data sharing in the cloud and IoT. This work outlines our research contribution towards secure data sharing in the cloud and IoT. For secure data sharing in the cloud, this work proposes several novel attribute-based encryption schemes. The core contributions to this end are efficient revocation, prevention of collusion attacks, and multi-group support. On the other hand, for secure data sharing in IoT, a permissioned blockchain-based access control system has been proposed. The system can be used to enforce fine-grained access control on IoT data where the access control decision is made by the blockchain-based on the consensus of the participating nodes”--Abstract, page iv

    Formally based semi-automatic implementation of an open security protocol

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    International audienceThis paper presents an experiment in which an implementation of the client side of the SSH Transport Layer Protocol (SSH-TLP) was semi-automatically derived according to a model-driven development paradigm that leverages formal methods in order to obtain high correctness assurance. The approach used in the experiment starts with the formalization of the protocol at an abstract level. This model is then formally proved to fulfill the desired secrecy and authentication properties by using the ProVerif prover. Finally, a sound Java implementation is semi-automatically derived from the verified model using an enhanced version of the Spi2Java framework. The resulting implementation correctly interoperates with third party servers, and its execution time is comparable with that of other manually developed Java SSH-TLP client implementations. This case study demonstrates that the adopted model-driven approach is viable even for a real security protocol, despite the complexity of the models needed in order to achieve an interoperable implementation

    Remote Attacks on FPGA Hardware

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    Immer mehr Computersysteme sind weltweit miteinander verbunden und ĂŒber das Internet zugĂ€nglich, was auch die Sicherheitsanforderungen an diese erhöht. Eine neuere Technologie, die zunehmend als Rechenbeschleuniger sowohl fĂŒr eingebettete Systeme als auch in der Cloud verwendet wird, sind Field-Programmable Gate Arrays (FPGAs). Sie sind sehr flexible Mikrochips, die per Software konfiguriert und programmiert werden können, um beliebige digitale Schaltungen zu implementieren. Wie auch andere integrierte Schaltkreise basieren FPGAs auf modernen Halbleitertechnologien, die von Fertigungstoleranzen und verschiedenen Laufzeitschwankungen betroffen sind. Es ist bereits bekannt, dass diese Variationen die ZuverlĂ€ssigkeit eines Systems beeinflussen, aber ihre Auswirkungen auf die Sicherheit wurden nicht umfassend untersucht. Diese Doktorarbeit befasst sich mit einem Querschnitt dieser Themen: Sicherheitsprobleme die dadurch entstehen wenn FPGAs von mehreren Benutzern benutzt werden, oder ĂŒber das Internet zugĂ€nglich sind, in Kombination mit physikalischen Schwankungen in modernen Halbleitertechnologien. Der erste Beitrag in dieser Arbeit identifiziert transiente Spannungsschwankungen als eine der stĂ€rksten Auswirkungen auf die FPGA-Leistung und analysiert experimentell wie sich verschiedene Arbeitslasten des FPGAs darauf auswirken. In der restlichen Arbeit werden dann die Auswirkungen dieser Spannungsschwankungen auf die Sicherheit untersucht. Die Arbeit zeigt, dass verschiedene Angriffe möglich sind, von denen frĂŒher angenommen wurde, dass sie physischen Zugriff auf den Chip und die Verwendung spezieller und teurer Test- und MessgerĂ€te erfordern. Dies zeigt, dass bekannte Isolationsmaßnahmen innerhalb FPGAs von böswilligen Benutzern umgangen werden können, um andere Benutzer im selben FPGA oder sogar das gesamte System anzugreifen. Unter Verwendung von Schaltkreisen zur Beeinflussung der Spannung innerhalb eines FPGAs zeigt diese Arbeit aktive Angriffe, die Fehler (Faults) in anderen Teilen des Systems verursachen können. Auf diese Weise sind Denial-of-Service Angriffe möglich, als auch Fault-Angriffe um geheime SchlĂŒsselinformationen aus dem System zu extrahieren. DarĂŒber hinaus werden passive Angriffe gezeigt, die indirekt die Spannungsschwankungen auf dem Chip messen. Diese Messungen reichen aus, um geheime SchlĂŒsselinformationen durch Power Analysis Seitenkanalangriffe zu extrahieren. In einer weiteren Eskalationsstufe können sich diese Angriffe auch auf andere Chips auswirken die an dasselbe Netzteil angeschlossen sind wie der FPGA. Um zu beweisen, dass vergleichbare Angriffe nicht nur innerhalb FPGAs möglich sind, wird gezeigt, dass auch kleine IoT-GerĂ€te anfĂ€llig fĂŒr Angriffe sind welche die gemeinsame Spannungsversorgung innerhalb eines Chips ausnutzen. Insgesamt zeigt diese Arbeit, dass grundlegende physikalische Variationen in integrierten Schaltkreisen die Sicherheit eines gesamten Systems untergraben können, selbst wenn der Angreifer keinen direkten Zugriff auf das GerĂ€t hat. FĂŒr FPGAs in ihrer aktuellen Form mĂŒssen diese Probleme zuerst gelöst werden, bevor man sie mit mehreren Benutzern oder mit Zugriff von Drittanbietern sicher verwenden kann. In Veröffentlichungen die nicht Teil dieser Arbeit sind wurden bereits einige erste Gegenmaßnahmen untersucht
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