There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

2 1 The innovative transport systems and the CityMobil project 10 1.1 The research questions 10 2 The state of art in the field of automatic transport systems 12 2.1 Case studies and demand studies for innovative transport systems 12 3 The design and implementation of surveys 14 3.1 Definition of experimental design 14 3.2 Questionnaire design and delivery 16 3.3 First analyses on the collected sample 18 4 Calibration of Logit Multionomial demand models 21 4.1 Methodology 21 4.2 Calibration of the “full” model. 22 4.3 Calibration of the “final” model 24 4.4 The demand analysis through the final Multinomial Logit model 25 5 The analysis of interaction between the demand and socioeconomic attributes 31 5.1 Methodology 31 5.2 Application of Mixed Logit models to the demand 31 5.3 Analysis of the interactions between demand and socioeconomic attributes through Mixed Logit models 32 5.4 Mixed Logit model and interaction between age and the demand for the CTS 38 5.5 Demand analysis with Mixed Logit model 39 6 Final analyses and conclusions 45 6.1 Comparison between the results of the analyses 45 6.2 Conclusions 48 6.3 Answers to the research questions and future developments 52

The European commission

We present Tor, a circuit-based low-latency anonymous communication service. This second-generation Onion Routing system addresses limitations in the original design by adding perfect forward secrecy, congestion control, directory servers, integrity checking, configurable exit policies, and a practical design for location-hidden services via rendezvous points. Tor works on the real-world Internet, requires no special privileges or kernel modifications, requires little synchronization or coordination between nodes, and provides a reasonable tradeoff between anonymity, usability, and efficiency. We briefly describe our experiences with an international network of more than 30 nodes. We close with a list of open problems in anonymous communication.

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Tor: the second-generation onion router

Social Network Analysis

National Institute of Standards and Technology における超伝導研究及び生活

We study the effect compulsion attacks, through which an adversary can request a decryption or key from an honest node, have on the security of mix based anonymous communication systems. Some specific countermeasures are proposed that increase the cost of compulsion attacks, detect that tracing is taking place and ultimately allow for some anonymity to be preserved even when all nodes are under compulsion. Going beyond the case when a single message is traced, we also analyze the effect of multiple messages being traced and devise some techniques that could retain some anonymity. Our analysis highlights that we can reason about plausible deniability in terms of the information theoretic anonymity metrics. © Springer-Verlag Berlin Heidelberg 2005.

Compulsion resistant anonymous communications

Distributed Hash Tables (DHTs) are very efficient distributed systems for routing, but at the same time vulnerable to disruptive nodes. Designers of such systems want them used in open networks, where an adversary can perform a sybil attack by introducing a large number of corrupt nodes in the network, considerably degrading its performance. We introduce a routing strategy that alleviates some of the effects of such an attack by making sure that lookups are performed using a diverse set of nodes. This ensures that at least some of the nodes queried are good, and hence the search makes forward progress. This strategy makes use of latent social information present in the introduction graph of the network. © Springer-Verlag Berlin Heidelberg 2005.

Sybil-resistant DHT routing

Malware concealment is the predominant strategy for malware propagation. Black hats create variants of malware based on polymorphism and metamorphism. Malware variants, by definition, share some information. Although the concealment strategy alters this information, there are still patterns on the software. Given a zoo of labelled malware and benign-ware, we ask whether a suspect program is more similar to our malware or to our benign-ware. Normalized Compression Distance (NCD) is a generic metric that measures the shared information content of two strings. This measure opens a new front in the malware arms race, one where the countermeasures promise to be more costly for malware writers, who must now obfuscate patterns as strings qua strings, without reference to execution, in their variants. Our approach classifies disk-resident malware with 97.4% accuracy and a false positive rate of 3%. We demonstrate that its accuracy can be improved by combining NCD with the compressibility rates of executables using decision forests, paving the way for future improvements. We demonstrate that malware reported within a narrow time frame of a few days is more homogeneous than malware reported over two years, but that our method still classifies the latter with 95.2% accuracy and a 5% false positive rate. Due to its use of compression, the time and computation cost of our method is nontrivial. We show that simple approximation techniques can improve its running time by up to 63%. We compare our results to the results of applying the 59 anti-malware programs used on the VirusTotal website to our malware. Our approach outperforms each one used alone and matches that of all of them used collectively.

https://www.mdpi.com/1099-4300/22/5/575/pdf

Detecting Malware with Information Complexity

Personalised social search is a promising avenue to increase the relevance of search engine results by making use of recommendations made by friends in a social network. More generally a whole class of systems take user preferences, aggregate and process them, before providing a view of the result to others in a social network. Yet, those systems present privacy risks, and could be used by spammers to propagate their malicious preferences. We present a general framework to preserve privacy while maximizing the benefit of sharing information in a social network, as well as a concrete proposal making use of cohesive social group concepts from social network analysis. We show that privacy can be guaranteed in a k-anonymity manner, and disruption through spam is kept to a minimum in a real world social network. © 2010 Springer-Verlag Berlin Heidelberg.

How to share your favourite search results while preserving privacy and quality

We present traffic analyses of two anonymous communications schemes that build on the classic Crowds/Hordes protocols. The AJSS10 [1] scheme combines multiple Crowds-like forward channels with a Hordes reply channel in an attempt to offer robustness in a mobile environment. We show that the resulting scheme fails to guarantee the claimed k-anonymity, and is in fact more vulnerable to malicious peers than Hordes, while suffering from higher latency. Similarly, the RWS11 [15] scheme invokes multiple instances of Crowds to provide receiver anonymity. We demonstrate that the sender anonymity of the scheme is susceptible to a variant of the predecessor attack [21], while receiver anonymity is fully compromised with an active attack. We conclude that the heuristic security claims of AJSS10 and RWS11 do not hold, and argue that composition of multiple anonymity channels can in fact weaken overall security. In contrast, we provide a rigorous security analysis of Hordes under the same threat model, and reflect on design principles for future anonymous channels to make them amenable to such security analysis. © 2013 Springer-Verlag.

George Danezis

Papers

Compulsion resistant anonymous communications

Sybil-resistant DHT routing

Detecting Malware with Information Complexity

How to share your favourite search results while preserving privacy and quality

The dangers of composing anonymous channels