304 research outputs found
Input-shrinking functions: theory and application
In this thesis, we contribute to the emerging field of the Leakage-Resilient Cryptography by studying the problem of secure data storage on hardware that may
leak information, introducing a new primitive, a leakage-resilient storage, and showing two different constructions of such storage scheme provably secure against a class of
leakage functions that can depend only on some restricted part of the memory and against a class of computationally weak leakage functions, e.g. functions computable by small circuits,
respectively.
Our results come with instantiations and analysis of concrete parameters.
Furthermore, as second contribution, we present our implementation in C programming language, using the cryptographic library of the OpenSSL project, of a two-party Authenticated Key
Exchange (AKE) protocol, which allows a client and a server, who share a huge secret file, to securely compute a shared key, providing client-to-server authentication, also in the presence of active attackers.
Following the work of Cash et al. (TCC 2007), we based our construction on a Weak Key Exchange (WKE) protocol, developed in the BRM, and a Password-based Authenticated Key
Exchange (PAKE) protocol secure in the Universally Composable (UC) framework.
The WKE protocol showed by Cash et al. uses an explicit construction of averaging sampler, which uses less random bits than the random choice but does not seem to be
efficiently implementable in practice.
In this thesis, we propose a WKE protocol similar but simpler than that one of Cash et al.: our protocol uses more randomness than the Cash et al.'s one, as it simply uses random
choice instead of averaging sampler, but we are able to show an efficient implementation of it.
Moreover, we formally adapt the security analysis of the WKE protocol of Cash et al. to our WKE protocol.
To complete our AKE protocol, we implement the PAKE protocol showed secure in the UC framework by Abdalla et al. (CT-RSA 2008), which is more efficient than the Canetti et al.'s UC-PAKE protocol (EuroCrypt 2005) used in Cash et al.'s work.
In our implementation of the WKE protocol, to achieve small constant communication complexity and amount of randomness, we rely on the Random Oracle (RO) model.
However, we would like to note that in our implementation of the AKE protocol we need also a UC-PAKE protocol which already relies on RO, as it is impossible to achieve UC-PAKE in the
standard model.
In our work we focus not only on the theoretical aspects of the area, providing formal models and proofs, but also on the practical ones, analyzing instantiations, concrete parameters
and implementation of the proposed solutions, to contribute to bridge the gap between theory and practice in this field
Dordis: Efficient Federated Learning with Dropout-Resilient Differential Privacy
Federated learning (FL) is increasingly deployed among multiple clients to
train a shared model over decentralized data. To address privacy concerns, FL
systems need to safeguard the clients' data from disclosure during training and
control data leakage through trained models when exposed to untrusted domains.
Distributed differential privacy (DP) offers an appealing solution in this
regard as it achieves a balanced tradeoff between privacy and utility without a
trusted server. However, existing distributed DP mechanisms are impractical in
the presence of client dropout, resulting in poor privacy guarantees or
degraded training accuracy. In addition, these mechanisms suffer from severe
efficiency issues.
We present Dordis, a distributed differentially private FL framework that is
highly efficient and resilient to client dropout. Specifically, we develop a
novel `add-then-remove' scheme that enforces a required noise level precisely
in each training round, even if some sampled clients drop out. This ensures
that the privacy budget is utilized prudently, despite unpredictable client
dynamics. To boost performance, Dordis operates as a distributed parallel
architecture via encapsulating the communication and computation operations
into stages. It automatically divides the global model aggregation into several
chunk-aggregation tasks and pipelines them for optimal speedup. Large-scale
deployment evaluations demonstrate that Dordis efficiently handles client
dropout in various realistic FL scenarios, achieving the optimal
privacy-utility tradeoff and accelerating training by up to 2.4
compared to existing solutions.Comment: This article has been accepted to ACM EuroSys '2
A Pairing-Free, One Round Identity Based Authenticated Key Exchange Protocol Secure Against Memory-Scrapers
Security of a key exchange protocol is formally established through an abstract game between a challenger and an adversary. In this game the adversary can get various information which are modeled by giving the adversary access to appropriate oracle queries. Empowered with all these information, the adversary will try to break the protocol. This is modeled by a test query which asks the adversary to distinguish between a session key of a fresh session from a random session key; properly guessing which correctly leads the adversary to win the game. In this traditional model of security the adversary sees nothing apart from the input/ output relationship of the algorithms. However, in recent past an adversary could obtain several additional information beyond what he gets to learn in these black box models of computation, thanks to the availability of powerful malwares. This data exfiltration due to the attacks of Memory Scraper/Ram-Scraper-type malwares is an emerging threat. In order to realistically capture these advanced classes of threats posed by such malwares we propose a new security model for identity-based authenticated key exchange (ID-AKE) which we call the Identity based Strong Extended Canetti Krawzyck (ID-seCK) model. Our security model captures leakages of intermediate values by appropriate oracle queries given to the adversary. Following this, we propose a round optimal (i.e., single round) ID-AKE protocol for two-party settings. Our design assumes a hybrid system equipped with a bare minimal Trusted Platform Module (TPM) that can only perform group exponentiations. One of the major advantages of our construction is that it does not involve any pairing operations, works in prime order group and have a tight security reduction to the Gap Diffie Hellman (GDH) problem under our new ID-seCK model. Our scheme also has the
capability to handle active adversaries while most of the previous ID-AKE protocols are secure only against passive adversaries. The security of our protocol is proved in the Random Oracle (RO) model
A Survey of Leakage-Resilient Cryptography
In the past 15 years, cryptography has made considerable progress in expanding the adversarial attack model to cover side-channel attacks, and has built schemes to provably defend against some of them. This survey covers the main models and results in this so-called leakage-resilient cryptography
Security of Ubiquitous Computing Systems
The chapters in this open access book arise out of the EU Cost Action project Cryptacus, the objective of which was to improve and adapt existent cryptanalysis methodologies and tools to the ubiquitous computing framework. The cryptanalysis implemented lies along four axes: cryptographic models, cryptanalysis of building blocks, hardware and software security engineering, and security assessment of real-world systems. The authors are top-class researchers in security and cryptography, and the contributions are of value to researchers and practitioners in these domains. This book is open access under a CC BY license
User-Centric Security and Privacy Mechanisms in Untrusted Networking and Computing Environments
Our modern society is increasingly relying on the collection, processing, and sharing of digital information. There are two fundamental trends: (1) Enabled by the rapid developments in sensor, wireless, and networking technologies, communication and networking are becoming more and more pervasive and ad hoc. (2) Driven by the explosive growth of hardware and software capabilities, computation power is becoming a public utility and information is often stored in centralized servers which facilitate ubiquitous access and sharing. Many emerging platforms and systems hinge on both dimensions, such as E-healthcare and Smart Grid. However, the majority information handled by these critical systems is usually sensitive and of high value, while various security breaches could compromise the social welfare of these systems. Thus there is an urgent need to develop security and privacy mechanisms to protect the authenticity, integrity and confidentiality of the collected data, and to control the disclosure of private information. In achieving that, two unique challenges arise: (1) There lacks centralized trusted parties in pervasive networking; (2) The remote data servers tend not to be trusted by system users in handling their data. They make existing security solutions developed for traditional networked information systems unsuitable. To this end, in this dissertation we propose a series of user-centric security and privacy mechanisms that resolve these challenging issues in untrusted network and computing environments, spanning wireless body area networks (WBAN), mobile social networks (MSN), and cloud computing. The main contributions of this dissertation are fourfold. First, we propose a secure ad hoc trust initialization protocol for WBAN, without relying on any pre-established security context among nodes, while defending against a powerful wireless attacker that may or may not compromise sensor nodes. The protocol is highly usable for a human user. Second, we present novel schemes for sharing sensitive information among distributed mobile hosts in MSN which preserves user privacy, where the users neither need to fully trust each other nor rely on any central trusted party. Third, to realize owner-controlled sharing of sensitive data stored on untrusted servers, we put forward a data access control framework using Multi-Authority Attribute-Based Encryption (ABE), that supports scalable fine-grained access and on-demand user revocation, and is free of key-escrow. Finally, we propose mechanisms for authorized keyword search over encrypted data on untrusted servers, with efficient multi-dimensional range, subset and equality query capabilities, and with enhanced search privacy. The common characteristic of our contributions is they minimize the extent of trust that users must place in the corresponding network or computing environments, in a way that is user-centric, i.e., favoring individual owners/users
Identity Management and Authorization Infrastructure in Secure Mobile Access to Electronic Health Records
We live in an age of the mobile paradigm of anytime/anywhere access, as the mobile device
is the most ubiquitous device that people now hold. Due to their portability, availability, easy
of use, communication, access and sharing of information within various domains and areas of
our daily lives, the acceptance and adoption of these devices is still growing. However, due to
their potential and raising numbers, mobile devices are a growing target for attackers and, like
other technologies, mobile applications are still vulnerable.
Health information systems are composed with tools and software to collect, manage, analyze
and process medical information (such as electronic health records and personal health records).
Therefore, such systems can empower the performance and maintenance of health services,
promoting availability, readability, accessibility and data sharing of vital information about a
patients overall medical history, between geographic fragmented health services. Quick access
to information presents a great importance in the health sector, as it accelerates work processes,
resulting in better time utilization. Additionally, it may increase the quality of care.
However health information systems store and manage highly sensitive data, which raises serious
concerns regarding patients privacy and safety, and may explain the still increasing number
of malicious incidents reports within the health domain.
Data related to health information systems are highly sensitive and subject to severe legal
and regulatory restrictions, that aim to protect the individual rights and privacy of patients.
Along side with these legislations, security requirements must be analyzed and measures implemented.
Within the necessary security requirements to access health data, secure authentication,
identity management and access control are essential to provide adequate means to
protect data from unauthorized accesses. However, besides the use of simple authentication
models, traditional access control models are commonly based on predefined access policies
and roles, and are inflexible. This results in uniform access control decisions through people,
different type of devices, environments and situational conditions, and across enterprises, location
and time.
Although already existent models allow to ensure the needs of the health care systems, they still
lack components for dynamicity and privacy protection, which leads to not have desire levels
of security and to the patient not to have a full and easy control of his privacy. Within this
master thesis, after a deep research and review of the stat of art, was published a novel dynamic
access control model, Socio-Technical Risk-Adaptable Access Control modEl (SoTRAACE),
which can model the inherent differences and security requirements that are present in this
thesis. To do this, SoTRAACE aggregates attributes from various domains to help performing
a risk assessment at the moment of the request. The assessment of the risk factors identified
in this work is based in a Delphi Study. A set of security experts from various domains were
selected, to classify the impact in the risk assessment of each attribute that SoTRAACE aggregates.
SoTRAACE was integrated in an architecture with requirements well-founded, and based
in the best recommendations and standards (OWASP, NIST 800-53, NIST 800-57), as well based in
deep review of the state-of-art. The architecture is further targeted with the essential security
analysis and the threat model. As proof of concept, the proposed access control model was implemented within the user-centric
architecture, with two mobile prototypes for several types of accesses by patients and healthcare
professionals, as well the web servers that handles the access requests, authentication and
identity management.
The proof of concept shows that the model works as expected, with transparency, assuring privacy
and data control to the user without impact for user experience and interaction. It is clear
that the model can be extended to other industry domains, and new levels of risks or attributes
can be added because it is modular. The architecture also works as expected, assuring secure
authentication with multifactor, and secure data share/access based in SoTRAACE decisions.
The communication channel that SoTRAACE uses was also protected with a digital certificate.
At last, the architecture was tested within different Android versions, tested with static and
dynamic analysis and with tests with security tools.
Future work includes the integration of health data standards and evaluating the proposed system
by collecting users’ opinion after releasing the system to real world.Hoje em dia vivemos em um paradigma móvel de acesso em qualquer lugar/hora, sendo que
os dispositivos móveis são a tecnologia mais presente no dia a dia da sociedade. Devido à sua
portabilidade, disponibilidade, fácil manuseamento, poder de comunicação, acesso e partilha
de informação referentes a várias áreas e domínios das nossas vidas, a aceitação e integração
destes dispositivos é cada vez maior. No entanto, devido ao seu potencial e aumento do número
de utilizadores, os dispositivos móveis são cada vez mais alvos de ataques, e tal como outras
tecnologias, aplicações móveis continuam a ser vulneráveis.
Sistemas de informação de saúde são compostos por ferramentas e softwares que permitem
recolher, administrar, analisar e processar informação médica (tais como documentos de saúde
eletrónicos). Portanto, tais sistemas podem potencializar a performance e a manutenção dos
serviços de saúde, promovendo assim a disponibilidade, acessibilidade e a partilha de dados
vitais referentes ao registro médico geral dos pacientes, entre serviços e instituições que estão
geograficamente fragmentadas. O rápido acesso a informações médicas apresenta uma grande
importância para o setor da saúde, dado que acelera os processos de trabalho, resultando assim
numa melhor eficiência na utilização do tempo e recursos. Consequentemente haverá uma
melhor qualidade de tratamento. Porém os sistemas de informação de saúde armazenam e
manuseiam dados bastantes sensíveis, o que levanta sérias preocupações referentes à privacidade
e segurança do paciente. Assim se explica o aumento de incidentes maliciosos dentro do
domínio da saúde.
Os dados de saúde são altamente sensíveis e são sujeitos a severas leis e restrições regulamentares,
que pretendem assegurar a proteção dos direitos e privacidade dos pacientes, salvaguardando
os seus dados de saúde. Juntamente com estas legislações, requerimentos de segurança
devem ser analisados e medidas implementadas. Dentro dos requerimentos necessários
para aceder aos dados de saúde, uma autenticação segura, gestão de identidade e controlos de
acesso são essenciais para fornecer meios adequados para a proteção de dados contra acessos
não autorizados. No entanto, além do uso de modelos simples de autenticação, os modelos
tradicionais de controlo de acesso são normalmente baseados em políticas de acesso e cargos
pré-definidos, e são inflexíveis. Isto resulta em decisões de controlo de acesso uniformes para
diferentes pessoas, tipos de dispositivo, ambientes e condições situacionais, empresas, localizações
e diferentes alturas no tempo. Apesar dos modelos existentes permitirem assegurar
algumas necessidades dos sistemas de saúde, ainda há escassez de componentes para accesso
dinâmico e proteção de privacidade , o que resultam em níveis de segurança não satisfatórios e
em o paciente não ter controlo directo e total sobre a sua privacidade e documentos de saúde.
Dentro desta tese de mestrado, depois da investigação e revisão intensiva do estado da arte,
foi publicado um modelo inovador de controlo de acesso, chamado SoTRAACE, que molda as
diferenças de acesso inerentes e requerimentos de segurança presentes nesta tese. Para isto,
o SoTRAACE agrega atributos de vários ambientes e domínios que ajudam a executar uma avaliação
de riscos, no momento em que os dados são requisitados. A avaliação dos fatores de risco
identificados neste trabalho são baseados num estudo de Delphi. Um conjunto de peritos de
segurança de vários domínios industriais foram selecionados, para classificar o impacto de cada
atributo que o SoTRAACE agrega. O SoTRAACE foi integrado numa arquitectura para acesso a
dados médicos, com requerimentos bem fundados, baseados nas melhores normas e recomendações (OWASP, NIST 800-53, NIST 800-57), e em revisões intensivas do estado da arte. Esta
arquitectura é posteriormente alvo de uma análise de segurança e modelos de ataque.
Como prova deste conceito, o modelo de controlo de acesso proposto é implementado juntamente
com uma arquitetura focada no utilizador, com dois protótipos para aplicações móveis,
que providênciam vários tipos de acesso de pacientes e profissionais de saúde. A arquitetura é
constituída também por servidores web que tratam da gestão de dados, controlo de acesso e
autenticação e gestão de identidade. O resultado final mostra que o modelo funciona como esperado,
com transparência, assegurando a privacidade e o controlo de dados para o utilizador,
sem ter impacto na sua interação e experiência. Consequentemente este modelo pode-se extender
para outros setores industriais, e novos níveis de risco ou atributos podem ser adicionados
a este mesmo, por ser modular. A arquitetura também funciona como esperado, assegurando
uma autenticação segura com multi-fator, acesso e partilha de dados segura baseado em decisões
do SoTRAACE. O canal de comunicação que o SoTRAACE usa foi também protegido com
um certificado digital.
A arquitectura foi testada em diferentes versões de Android, e foi alvo de análise estática,
dinâmica e testes com ferramentas de segurança.
Para trabalho futuro está planeado a integração de normas de dados de saúde e a avaliação do
sistema proposto, através da recolha de opiniões de utilizadores no mundo real
Secure Session Framework: An Identity-based Cryptographic Key Agreement and Signature Protocol
Die vorliegende Dissertation beschäftigt sich mit der Methode der identitätsbasierten Verschlüsselung. Hierbei wird der Name oder die Identität eines Zielobjekts zum Verschlüsseln der Daten verwendet. Diese Eigenschaft macht diese Methode zu einem passenden Werkzeug für die moderne elektronische Kommunikation, da die dort verwendeten Identitäten oder Endpunktadressen weltweit eindeutig sein müssen. Das in der Arbeit entwickelte identitätsbasierte Schlüsseleinigungsprotokoll bietet Vorteile gegenüber existierenden Verfahren und eröffnet neue Möglichkeiten. Eines der Hauptmerkmale ist die komplette Unabhängigkeit der Schlüsselgeneratoren. Diese Unabhängigkeit ermöglicht es, dass verschiedene Sicherheitsdomänen ihr eigenes System aufsetzen können. Sie sind nicht mehr gezwungen, sich untereinander abzusprechen oder Geheimnisse auszutauschen. Auf Grund der Eigenschaften des Protokolls sind die Systeme trotzdem untereinander kompatibel. Dies bedeutet, dass Anwender einer Sicherheitsdomäne ohne weiteren Aufwand verschlüsselt mit Anwendern einer anderen Sicherheitsdomäne kommunizieren können. Die Unabhängigkeit wurde ebenfalls auf ein Signatur-Protokoll übertragen. Es ermöglicht, dass Benutzer verschiedener Sicherheitsdomänen ein Objekt signieren können, wobei auch der Vorgang des Signierens unabhängig sein kann. Neben dem Protokoll wurde in der Arbeit auch die Analyse von bestehenden Systemen durchgeführt. Es wurden Angriffe auf etablierte Protokolle und Vermutungen gefunden, die aufzeigen, ob oder in welchen Situationen diese nicht verwendet werden sollten. Dabei wurde zum einen eine komplett neue Herangehensweise gefunden, die auf der (Un-)Definiertheit von bestimmten Objekten in diskreten Räumen basiert. Zum anderen wurde die bekannte Analysemethode der Gitterreduktion benutzt und erfolgreich auf neue Bereiche übertragen. Schlussendlich werden in der Arbeit Anwendungsszenarien für das Protokoll vorgestellt, in denen dessen Vorteile besonders relevant sind. Das erste Szenario bezieht sich auf Telefonie, wobei die Telefonnummer einer Zielperson als Schlüssel verwendet. Sowohl GSM-Telefonie als auch VoIP-Telefonie werden in der Arbeit untersucht. Dafür wurden Implementierungen auf einem aktuellen Mobiltelefon durchgeführt und bestehende VoIP-Software erweitert. Das zweite Anwendungsbeispielsind IP-Netzwerke. Auch die Benutzung der IP-Adresse eines Rechners als Schlüssel ist ein gutes Beispiel, jedoch treten hier mehr Schwierigkeiten auf als bei der Telefonie. Es gibt beispielsweise dynamische IP-Adressen oder die Methode der textit{Network Address Translation}, bei der die IP-Adresse ersetzt wird. Diese und weitere Probleme wurden identifiziert und jeweils Lösungen erarbeitet
Security of Ubiquitous Computing Systems
The chapters in this open access book arise out of the EU Cost Action project Cryptacus, the objective of which was to improve and adapt existent cryptanalysis methodologies and tools to the ubiquitous computing framework. The cryptanalysis implemented lies along four axes: cryptographic models, cryptanalysis of building blocks, hardware and software security engineering, and security assessment of real-world systems. The authors are top-class researchers in security and cryptography, and the contributions are of value to researchers and practitioners in these domains. This book is open access under a CC BY license
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