No description available.

Kerberos is a widely-deployed network authentication protocol that is being considered for standardization. Like other standard protocols, Kerberos is no exception to security flaws and weaknesses, as has been demonstrated in several prior works. Provable security guarantees go a long way in restoring users' faith, thus making a protocol an even stronger candidate for standards. In this thesis, our goal was thus to provide provable security support for Kerberos and other practical protocols. Our contributions are three-fold: We first look at the symmetric encryption schemes employed in the current version 5 of Kerberos. Several recent results have analyzed a significant part of Kerberos v.5 using formal-methods-based approaches, which are meaningful only if the underlying encryption schemes satisfy strong cryptographic notions of privacy and authenticity. However, to our knowledge these schemes were never analyzed and proven to satisfy such notions. This thesis aims to bridge this gap. Our provable security analyses confirm that some of the encryption scheme options in Kerberos v.5 already provide privacy and authenticity, and for the remaining we suggest slight modifications for the same. We next turn our attention to the ways in which the keys and other random strings needed in cryptographic schemes employed by practical protocols are generated. Randomness needs to be carefully generated for the provable security guarantees to hold. We propose an efficient pseudorandom generator (PRG) based on hash functions. The security of our PRG relies on exponential collision-resistance and regularity of the underlying hash function. Our PRG can be used to generate various strings, like session keys, sequence numbers, confounders, etc., which are all suggested to be generated randomly in the Kerberos v.5 specification, but no algorithms are mentioned. Each of the above strings are required to satisfy different properties, all of which are trivially satisfied by the pseudorandom strings output by a PRG. Finally, we look at the problem of revocation associated with two relatively new types of encryption schemes: identity-based encryption (IBE) and attribute-based encryption (ABE). While these encryption schemes are relatively less efficient compared to public-key encryption schemes, they have already been used (and are very likely to be used in future, as well) in many practical protocols due to their attractive features. Any setting, public-key, identity-based, or attribute-based, must provide a means to revoke users from the system. However, unlike public-key encryption, there has been little prior work on studying the revocation mechanisms in an IBE or ABE. We propose new primitives and their efficient and provably secure instantiations, focusing on the revocation problem. We would like to note that even though all the results presented in this thesis are motivated mainly by provable security in practice, only the first bullet above has a direct impact on a practical and widely deployed protocol Kerberos. Our PRG is the most efficient construction among theoretical PRGs, but it may still not be efficient enough to be directly usable in practical protocols. And our results and techniques for revocation in IBE and ABE have found much wider applications in information security, such as mobile social networks, cloud-based secure health records, data outsourcing systems, vehicular ad-hoc networks, etc.

Yes / The recent advancements in wireless sensor hardware ensures sensing multiple sensor data such as temperature, pressure, humidity, etc. using a single hardware unit, thus defining it as multi-sensor data communication in wireless sensor networks (WSNs). The in-processing technique of data aggregation is crucial in energy-efficient WSNs; however, with the requirement of end-to-end data confidentiality it may prove to be a challenge. End-to-end data confidentiality along with data aggregation is possible with the implementation of a special type of encryption scheme called privacy homomorphic (PH) encryption schemes. This paper proposes an optimized PH encryption scheme for WSN integrated networks handling multi-sensor data. The proposed scheme ensures light-weight payloads, significant energy and bandwidth consumption along with lower latencies. The performance analysis of the proposed scheme is presented in this paper with respect to the existing scheme. The working principle of the multi-sensor data framework is also presented in this paper along with the appropriate packet structures and process. It can be concluded that the scheme proves to decrease the payload size by 56.86% and spend an average energy of 8-18 mJ at the aggregator node for sensor nodes varying from 10-50 thereby ensuring scalability of the WSN unlike the existing scheme.

The topic of this thesis is a cryptosystem, precisely a public key encryption scheme, that is based on the knapsack problem. At first we formulate terms like \mathcal{NP} -complete problem, one-way function, hard-core predicate, public key encryption scheme and semantic security which we connect in this thesis. After that we present the knapsack problem. Then we prove that the knapsack problem with appropriate parameters has a property that leads to semantic security of the encryption scheme which we present afterwards. This public key encryption scheme is based on the scheme proposed by Vadim Lyubashevsky, Adriana Palacio and Gil Segev. Powered by TCPDF (www.tcpdf.org)

<p>In service-oriented architecture, services can communicate and share data among themselves. This thesis presents a solution that allows detecting several types of data leakages made by authorized insiders to unauthorized services. My solution provides role-based and attribute-based access control for data so that each service can access only those data subsets for which the service is authorized, considering a context and service’s attributes such as security level of the web browser and trust level of service. My approach provides data protection in transit and at rest for both centralized and peer-to-peer service architectures. The methodology ensures confidentiality and integrity of data, including data stored in untrusted cloud. In addition to protecting data against malicious or curious cloud or database administrators, the capability of running a search through encrypted data, using SQL queries, and building analytics over encrypted data is supported. My solution is implemented in the “WAXEDPRUNE” (Web-based Access to Encrypted Data Processing in Untrusted Environments) project, funded by Northrop Grumman Cybersecurity Research Consortium. WAXEDPRUNE methodology is illustrated in this thesis for two use cases, including a Hospital Information System with secure storage and exchange of Electronic Health Records and a Vehicle-to-Everything communication system with secure exchange of vehicle’s and drivers’ data, as well as data on road events and road hazards. </p><p>To help with investigating data leakage incidents in service-oriented architecture, integrity of provenance data needs to be guaranteed. For that purpose, I integrate WAXEDPRUNE with IBM Hyperledger Fabric blockchain network, so that every data access, transfer or update is recorded in a public blockchain ledger, is non-repudiatable and can be verified at any time in the future. The work on this project, called “Blockhub,” is in progress.</p>

This work explains the fundamental definitions required to define and create Fuzzy Identity-Based Encryption schemes as an error-tolerant version of Identity-Based Encryption schemes, along with three different examples of such creations. These examples are Sahai-Waters' FIBE, Baek et al.'s EFIBE-I and EFIBE-II. The required Set-up, Key Generation, Encryption and Decryption algorithms for each scheme are formalized and the proofs of security using the Selective-ID model are introduced. Subtle differences between the three schemes are discussed, including their computational efficiency comparison. The writing is intended as a self-sufficient resource for readers, containing the schemes and background definitions.

La sécurité est une des préoccupations principales de l'informatique moderne. De plus en plus de personnes utilisent un ordinateur pour des opérations sensibles comme pour des transferts bancaires, des achats sur internet, le payement des impôts ou même pour voter. La plupart de ces utilisateurs ne savent pas comment la sécurité est assurée, par conséquence ils font totalement confiance à leurs applications. Souvent ces applications utilisent des protocoles cryptographiques qui sont sujet à erreur, comme le montre la célèbre faille de sécurité découverte sur le protocole de Needham-Schroeder dix-sept ans après sa publication. Ces erreurs proviennent de plusieurs aspects : -- Les preuves de primitives cryptographiques peuvent contenir des erreurs. -- Les propriétés de sécurité ne sont pas bien spécifiées, par conséquence, il n'est pas facile d'en faire la preuve. -- Les hypothèses faites sur le modèle de l'intrus sont trop restrictives. Dans cette habilitation, nous présentons des méthodes formelles pour vérifier la sécurité selon ces trois aspects. Tout d'abord, nous construisons des logiques de Hoare afin de prouver la sécurité de primitives cryptographiques comme les chiffrements à clef publique, les modes de chiffrement asymétriques et les codes d'authentification de message ( Message authentication codes, MACs). Nous étudions aussi les protocoles de votes électroniques et les réseaux de capteus sans fil ( Wireless Sensor Networks, WSNs ). Dans ces deux domaines, nous analysons les propriétés de sécurité afin de les modéliser formellement. Ensuite nous développons des techniques appropriées afin de les vérifier.