Index Terms-security, authentication, pin code Abstract-Touch screens have become ubiquitous in the past few years, like for instance in smartphones and tablets. These devices are often the entry door to numerous information systems, hence having a secure and practical authentication mechanism is crucial. In this paper, we examine the complexity of different authentication methods specifically designed for such devices.We study the widely spread technology to authenticate a user using a Personal Identifier Number code (PIN code). Entering the code is a critical moment where there are several possibilities for an attacker to discover the secret. We consider the three attack models: a Bruteforce Attack (BA) model , a Smudge Attack (SA) model, and an Observation Attack (OA) model where the attacker sees the user logging in on his device. The aim of the intruder is to learn the secret code.Our goal is to propose alternative methods to enter a PIN code. We compare such different methods in terms of security. Some methods require more intentional resources than other, this is why we performed a psychological study on the different methods to evaluate the users' perception of the different methods and their usage.
Delegating the computation of a polynomial to a server in a verifiable way is challenging. An even more challenging problem is ensuring that this polynomial remains hidden to clients who are able to query such a server. In this paper, we formally define the notion of Private Polynomial Evaluation (PPE). Our main contribution is to design a rigorous security model along with relations between the different security properties. We define polynomial protection (PP), proof unforgeability (UNF), and indistinguishability against chosen function attack (IND-CFA), which formalizes the resistance of a PPE against attackers trying to guess which polynomial is used among two polynomials of their choice. As a second contribution, we give a cryptanalysis of two PPE schemes of the literature. Finally, we design a PPE scheme called PIPE and we prove that it is PP-, UNFand IND-CFA-secure under the decisional Diffie-Hellman assumption in the random oracle model.
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