arXiv subjects

Stefan Rass

Publications and source records attributed to Stefan Rass.

45 records · Page 3Linked to original sources

arXiv2018

Community-Based Security for the Internet of Things

With more and more devices becoming connectable to the internet, the number of services but also a lot of threats increases dramatically. Security is often a secondary matter behind functionality and comfort, but the problem has already been recognized. Still, with many IoT devices being deployed already, security will come step-by-step and through updates, patches and new versions of apps and IoT software. While these updates can be safely retrieved from app stores, the problems kick in via jailbroken devices and with the variety of untrusted sources arising on the internet. Since hacking is typically a community effort? these days, security could be a community goal too. The challenges are manifold, and one reason for weak or absent security on IoT devices is their weak computational power. In this chapter, we discuss a community based security mechanism in which devices mutually aid each other in secure software management. We discuss game-theoretic methods of community formation and light-weight cryptographic means to accomplish authentic software deployment inside the IoT device community.

cs.CY↗

arXiv2018

Game Theory Meets Network Security: A Tutorial at ACM CCS

The increasingly pervasive connectivity of today's information systems brings up new challenges to security. Traditional security has accomplished a long way toward protecting well-defined goals such as confidentiality, integrity, availability, and authenticity. However, with the growing sophistication of the attacks and the complexity of the system, the protection using traditional methods could be cost-prohibitive. A new perspective and a new theoretical foundation are needed to understand security from a strategic and decision-making perspective. Game theory provides a natural framework to capture the adversarial and defensive interactions between an attacker and a defender. It provides a quantitative assessment of security, prediction of security outcomes, and a mechanism design tool that can enable security-by-design and reverse the attacker's advantage. This tutorial provides an overview of diverse methodologies from game theory that includes games of incomplete information, dynamic games, mechanism design theory to offer a modern theoretic underpinning of a science of cybersecurity. The tutorial will also discuss open problems and research challenges that the CCS community can address and contribute with an objective to build a multidisciplinary bridge between cybersecurity, economics, game and decision theory.

cs.CR↗

arXiv2017

Uncertainty in Cyber Security Investments

When undertaking cyber security risk assessments, we must assign numeric values to metrics to compute the final expected loss that represents the risk that an organization is exposed to due to cyber threats. Even if risk assessment is motivated from real-world observations and data, there is always a high chance of assigning inaccurate values due to different uncertainties involved (e.g., evolving threat landscape, human errors) and the natural difficulty of quantifying risk per se. Our previous work has proposed a model and a software tool that empowers organizations to compute optimal cyber security strategies given their financial constraints, i.e., available cyber security budget. We have also introduced a general game-theoretic model with uncertain payoffs (probability-distribution-valued payoffs) showing that such uncertainty can be incorporated in the game-theoretic model by allowing payoffs to be random. In this paper, we combine our aforesaid works and we conclude that although uncertainties in cyber security risk assessment lead, on average, to different cyber security strategies, they do not play significant role into the final expected loss of the organization when using our model and methodology to derive this strategies. We show that our tool is capable of providing effective decision support. To the best of our knowledge this is the first paper that investigates how uncertainties on various parameters affect cyber security investments.

cs.GT↗

arXiv2017

On Game-Theoretic Risk Management (Part Three) - Modeling and Applications

The game-theoretic risk management framework put forth in the precursor reports "Towards a Theory of Games with Payoffs that are Probability-Distributions" (arXiv:1506.07368 [q-fin.EC]) and "Algorithms to Compute Nash-Equilibria in Games with Distributions as Payoffs" (arXiv:1511.08591v1 [q-fin.EC]) is herein concluded by discussing how to integrate the previously developed theory into risk management processes. To this end, we discuss how loss models (primarily but not exclusively non-parametric) can be constructed from data. Furthermore, hints are given on how a meaningful game theoretic model can be set up, and how it can be used in various stages of the ISO 27000 risk management process. Examples related to advanced persistent threats and social engineering are given. We conclude by a discussion on the meaning and practical use of (mixed) Nash equilibria equilibria for risk management.

econ.GN↗

arXiv2017

Towards a Physical Oracle for the Partition Problem using Analogue Computing

Despite remarkable achievements in its practical tractability, the notorious class of NP-complete problems has been escaping all attempts to find a worst-case polynomial time-bound solution algorithms for any of them. The vast majority of work relies on Turing machines or equivalent models, all of which relate to digital computing. This raises the question of whether a computer that is (partly) non-digital could offer a new door towards an efficient solution. And indeed, the partition problem, which is another NP-complete sibling of the famous Boolean satisfiability problem SAT, might be open to efficient solutions using analogue computing. We investigate this hypothesis here, providing experimental evidence that Partition, and in turn also SAT, may become tractable on a combined digital and analogue computing machine. This work provides mostly theoretical and based on simulations, and as such does not exhibit a polynomial time algorithm to solve NP-complete problems. Instead, it is intended as a pointer to new directions of research on special-purpose computing architectures that may help handling the class NP efficiently.

cs.CC↗

arXiv2015

Oblivious Lookup Tables

We consider the following question: given a group-homomorphic public-key encryption $E$, a ciphertext $c=E(x,pk)$ hiding a value $x$ using a key $pk$, and a "suitable" description of a function $f$, can we evaluate $E(f(x), pk)$ without decrypting $c$? We call this an "oblivious lookup table" and show the existence of such a primitive. To this end, we describe a concrete construction, discuss its security and relations to other cryptographic primitives, and point out directions of future investigations towards generalizations.

cs.CR↗

arXiv2013

Blind Turing-Machines: Arbitrary Private Computations from Group Homomorphic Encryption

Secure function evaluation (SFE) is the process of computing a function (or running an algorithm) on some data, while keeping the input, output and intermediate results hidden from the environment in which the function is evaluated. This can be done using fully homomorphic encryption, Yao's garbled circuits or secure multiparty computation. Applications are manifold, most prominently the outsourcing of computations to cloud service providers, where data is to be manipulated and processed in full confidentiality. Today, one of the most intensively studied solutions to SFE is fully homomorphic encryption (FHE). Ever since the first such systems have been discovered in 2009, and despite much progress, FHE still remains inefficient and difficult to implement practically. Similar concerns apply to garbled circuits and (generic) multiparty computation protocols. In this work, we introduce the concept of a blind Turing-machine, which uses simple homomorphic encryption (an extension of ElGamal encryption) to process ciphertexts in the way as standard Turing-machines do, thus achieving computability of any function in total privacy. Remarkably, this shows that fully homomorphic encryption is indeed an overly strong primitive to do SFE, as group homomorphic encryption with equality check is already sufficient. Moreover, the technique is easy to implement and perhaps opens the door to efficient private computations on nowadays computing machinery, requiring only simple changes to well-established computer architectures.

cs.CR↗

arXiv2010

Fusion Discrete Logarithm Problems

The Discrete Logarithm Problem is well-known among cryptographers, for its computational hardness that grants security to some of the most commonly used cryptosystems these days. Still, many of these are limited to a small number of candidate algebraic structures which permit implementing the algorithms. In order to extend the applicability of discrete-logarithm-based cryptosystems to a much richer class of algebraic structures, we present a generalized form of exponential function. Our extension relaxes some assumptions on the exponent, which is no longer required to be an integer. Using an axiomatic characterization of the exponential function, we show how to construct mappings that obey the same rules as exponentials, but can raise vectors to the power of other vectors in an algebraically sound manner. At the same time, computational hardness is not affected (in fact, the problem could possibly be strengthened). Setting up standard cryptosystems in terms of our generalized exponential function is simple and requires no change to the existing security proofs. This opens the field for building much more general schemes than the ones known so far.

cs.CR↗

arXiv2009

Simple Error Scattering Model for improved Information Reconciliation

Implementations of quantum key distribution as available nowadays suffer from inefficiencies due to post processing of the raw key that severely cuts down the final secure key rate. We present a simple model for the error scattering across the raw key and derive "closed form" expressions for the probability of a parity check failure, or experiencing more than some fixed number of errors. Our results can serve for improvement for key establishment, as information reconciliation via interactive error correction and privacy amplification rests on mostly unproven assumptions. We support those hypotheses on statistical grounds.

stat.AP↗