Building and evaluating an inconspicuous smartphone authentication method

Tese de mestrado em Engenharia Informática, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2013Os smartphones que trazemos connosco estão cada vez mais entranhados nas nossas vidas intimas. Estes dispositivos possibilitam novas formas de trabalhar, de socializar, e ate de nos divertirmos. No entanto, também criaram novos riscos a nossa privacidade. Uma forma comum de mitigar estes riscos e configurar o dispositivo para bloquear apos um período de inatividade. Para voltar a utiliza-lo, e então necessário superar uma barreira de autenticação. Desta forma, se o aparelho cair das mãos de outra pessoa, esta não poderá utiliza-lo de forma a que tal constitua uma ameaça. O desbloqueio com autenticação e, assim, o mecanismo que comummente guarda a privacidade dos utilizadores de smartphones. Porem, os métodos de autenticação atualmente utilizados são maioritariamente um legado dos computadores de mesa. As palavras-passe e códigos de identificação pessoal são tornados menos seguros pelo facto de as pessoas criarem mecanismos para os memorizarem mais facilmente. Alem disso, introduzir estes códigos e inconveniente, especialmente no contexto móvel, em que as interações tendem a ser curtas e a necessidade de autenticação atrapalha a prossecução de outras tarefas. Recentemente, os smartphones Android passaram a oferecer outro método de autenticação, que ganhou um grau de adoção assinalável. Neste método, o código secreto do utilizador e uma sucessão de traços desenhados sobre uma grelha de 3 por 3 pontos apresentada no ecrã táctil. Contudo, quer os códigos textuais/numéricos, quer os padrões Android, são suscetíveis a ataques rudimentares. Em ambos os casos, o canal de entrada e o toque no ecrã táctil; e o canal de saída e o visual. Tal permite que outras pessoas possam observar diretamente a introdução da chave; ou que mais tarde consigam distinguir as marcas deixadas pelos dedos na superfície de toque. Alem disso, estes métodos não são acessíveis a algumas classes de utilizadores, nomeadamente os cegos. Nesta dissertação propõe-se que os métodos de autenticação em smartphones podem ser melhor adaptados ao contexto móvel. Nomeadamente, que a possibilidade de interagir com o dispositivo de forma inconspícua poderá oferecer aos utilizadores um maior grau de controlo e a capacidade de se auto-protegerem contra a observação do seu código secreto. Nesse sentido, foi identificada uma modalidade de entrada que não requer o canal visual: sucessões de toques independentes de localização no ecrã táctil. Estes padrões podem assemelhar-se (mas não estão limitados) a ritmos ou código Morse. A primeira contribuição deste trabalho e uma técnica algorítmica para a deteção destas sucessões de toques, ou frases de toque, como chaves de autenticação. Este reconhecedor requer apenas uma demonstração para configuração, o que o distingue de outras abordagens que necessitam de vários exemplos para treinar o algoritmo. O reconhecedor foi avaliado e demonstrou ser preciso e computacionalmente eficiente. Esta contribuição foi enriquecida com o desenvolvimento de uma aplicação Android que demonstra o conceito. A segunda contribuição e uma exploração de fatores humanos envolvidos no uso de frases de toque para autenticação. E consubstanciada em três estudos com utilizadores, em que o método de autenticação proposto e comparado com as alternativas mais comuns: PIN e o padrão Android. O primeiro estudo (N=30) compara os três métodos no que que diz respeito a resistência a observação e à usabilidade, entendida num sentido lato, que inclui a experiencia de utilização (UX). Os resultados sugerem que a usabilidade das três abordagens e comparável, e que em condições de observação perfeitas, nos três casos existe grande viabilidade de sucesso para um atacante. O segundo estudo (N=19) compara novamente os três métodos mas, desta feita, num cenário de autenticação inconspícua. Com efeito, os participantes tentaram introduzir os códigos com o dispositivo situado por baixo de uma mesa, fora do alcance visual. Neste caso, demonstra-se que a autenticação com frases de toque continua a ser usável. Já com as restantes alternativas existe uma diminuição substancial das medidas de usabilidade. Tal sugere que a autenticação por frases de toque suporta a capacidade de interação inconspícua, criando assim a possibilidade de os utilizadores se protegerem contra possíveis atacantes. O terceiro estudo (N=16) e uma avaliação de usabilidade e aceitação do método de autenticação com utilizadores cegos. Neste estudo, são também elicitadas estratégias de ocultação suportadas pela autenticação por frases de toque. Os resultados sugerem que a técnica e também adequada a estes utilizadores.As our intimate lives become more tangled with the smartphones we carry, privacy has become an increasing concern. A widely available option to mitigate security risks is to set a device so that it locks after a period of inactivity, requiring users to authenticate for subsequent use. Current methods for establishing one's identity are known to be susceptible to even rudimentary observation attacks. The mobile context in which interactions with smartphones are prone to occur further facilitates shoulder-surfing. We submit that smartphone authentication methods can be better adapted to the mobile context. Namely, the ability to interact with the device in an inconspicuous manner could offer users more control and the ability to self-protect against observation. Tapping is a communication modality between a user and a device that can be appropriated for that purpose. This work presents a technique for employing sequences of taps, or tap phrases, as authentication codes. An efficient and accurate tap phrase recognizer, that does not require training, is presented. Three user studies were conducted to compare this approach to the current leading methods. Results indicate that the tapping method remains usable even under inconspicuous authentications scenarios. Furthermore, we found that it is appropriate for blind users, to whom usability barriers and security risks are of special concern

XESS: The XML expert system shell

The XML Expert System Shell (XESS) was designed to alleviate some of the difficulties associated with translating a knowledge base from one expert system to another. The major goal of XESS is to allow programmers to model an expert system, complete with traditional facts and rules, in an XML-based language that leverages the universally understood terms used when teaching artificial intelligence to students. XML, the extensible markup language, is a text-based standard for information interchange between disparate systems1; it was originally designed to represent data in an easily parsable, human readable format2. While some extensions of the XML specification, particularly the Simple Object Access Protocol (SOAP), have long since abandoned human readability, the core XML specification is still used frequently to produce documents that can easily be exchanged between computational platforms and created or understood by human beings. The XESS-XML language inherits all of the usability of XML; it can be edited by hand in any text editor, is human readable, and can be parsed using XML parsers commonly available in any modern programming language. The XML Schema specification provides a mechanism for explicitly defining the content of an XML document so that a document can be validated3,4,5. XML schemas specify the make-up of an XML document in exacting detail6, using a pseudo-object-oriented syntax to specify exactly which entities are allowed in the document, the attributes of those entities, where they are allowed in the document, and how often they may occur. The XESS-XML language is defined as a fully extensible XML Schema, which can be used to validate any knowledge base written in the language. The Schema provides entities for common facts (e.g. predictes, structs) and a robust syntax for expressing rules in an if-then-else format, as well as the actions that should be taken in the event that a rule is fired. Additionally, because XML schemas are fully extensible, the XESS schema may be extended to add additional functionality such as support for fuzzy logic, new clause types, or new actions to be taken when rules are fired. In addition to the XML language, XESS also includes an object oriented interpreter specification that defines a robust set of language independent APIs for interacting with the expert system. This interpreter specification is meant to set expectations, both for XESS developers and users, as to the features provided by the XESS API regardless of the language in which the interpreter has been implemented. As part of the specification, the XESS API also provides object oriented definitions for XESS plug-ins; a plug-in is capable of translating from an XESS document to the native language of a specific expert system shell in a generic way (i.e. not specific to any one rule set) and back again. This allows users to express custom expert system shells in the XESS-XML language, parse them using an XESS interpreter written in any language, and translate them to a specific expert system shell through the use of an XESS plug-in without needing to learn the specific expert system shell language or rewriting the knowledge base once for each shell tested

Keystroke dynamics as a biometric

Modern computer systems rely heavily on methods of authentication and identity verification to protect sensitive data. One of the most robust protective techniques involves adding a layer of biometric analysis to other security mechanisms, as a means of establishing the identity of an individual beyond reasonable doubt. In the search for a biometric technique which is both low-cost and transparent to the end user, researchers have considered analysing the typing patterns of keyboard users to determine their characteristic timing signatures.Previous research into keystroke analysis has either required fixed performance of known keyboard input or relied on artificial tests involving the improvisation of a block of text for analysis. I is proposed that this is insufficient to determine the nature of unconstrained typing in a live computing environment. In an attempt to assess the utility of typing analysis for improving intrusion detection on computer systems, we present the notion of ‘genuinely free text’ (GFT). Through the course of this thesis, we discuss the nature of GFT and attempt to address whether it is feasible to produce a lightweight software platform for monitoring GFT keystroke biometrics, while protecting the privacy of users.The thesis documents in depth the design, development and deployment of the multigraph-based BAKER software platform, a system for collecting statistical GFT data from live environments. This software platform has enabled the collection of an extensive set of keystroke biometric data for a group of participating computer users, the analysis of which we also present here. Several supervised learning techniques were used to demonstrate that the richness of keystroke information gathered from BAKER is indeed sufficient to recommend multigraph keystroke analysis, as a means of augmenting computer security. In addition, we present a discussion of the feasibility of applying data obtained from GFT profiles in circumventing traditional static and free text analysis biometrics

PCPT and ACPT: Copyright Protection and Traceability Scheme for DNN Models

Deep neural networks (DNNs) have achieved tremendous success in artificial intelligence (AI) fields. However, DNN models can be easily illegally copied, redistributed, or abused by criminals, seriously damaging the interests of model inventors. The copyright protection of DNN models by neural network watermarking has been studied, but the establishment of a traceability mechanism for determining the authorized users of a leaked model is a new problem driven by the demand for AI services. Because the existing traceability mechanisms are used for models without watermarks, a small number of false-positives are generated. Existing black-box active protection schemes have loose authorization control and are vulnerable to forgery attacks. Therefore, based on the idea of black-box neural network watermarking with the video framing and image perceptual hash algorithm, a passive copyright protection and traceability framework PCPT is proposed that uses an additional class of DNN models, improving the existing traceability mechanism that yields a small number of false-positives. Based on an authorization control strategy and image perceptual hash algorithm, a DNN model active copyright protection and traceability framework ACPT is proposed. This framework uses the authorization control center constructed by the detector and verifier. This approach realizes stricter authorization control, which establishes a strong connection between users and model owners, improves the framework security, and supports traceability verification

Quality assessment technique for ubiquitous software and middleware

The new paradigm of computing or information systems is ubiquitous computing systems. The technology-oriented issues of ubiquitous computing systems have made researchers pay much attention to the feasibility study of the technologies rather than building quality assurance indices or guidelines. In this context, measuring quality is the key to developing high-quality ubiquitous computing products. For this reason, various quality models have been defined, adopted and enhanced over the years, for example, the need for one recognised standard quality model (ISO/IEC 9126) is the result of a consensus for a software quality model on three levels: characteristics, sub-characteristics, and metrics. However, it is very much unlikely that this scheme will be directly applicable to ubiquitous computing environments which are considerably different to conventional software, trailing a big concern which is being given to reformulate existing methods, and especially to elaborate new assessment techniques for ubiquitous computing environments. This paper selects appropriate quality characteristics for the ubiquitous computing environment, which can be used as the quality target for both ubiquitous computing product evaluation processes ad development processes. Further, each of the quality characteristics has been expanded with evaluation questions and metrics, in some cases with measures. In addition, this quality model has been applied to the industrial setting of the ubiquitous computing environment. These have revealed that while the approach was sound, there are some parts to be more developed in the future