Sharif Digital Repository

Today one of the most important challenges of internet is protecting the privacy of its users. Now, there are just a few practical anonymity systems over internet and one prominent is Tor anonymity network that works based on well-known onion routing. Although Tor is designed for providing low latency anonymity, but its users face long delays using this network and most of them do not tolerate these delays. So they leave the network and this leads to decreasing the members of anonymity set and in a smaller anonymity set, it’s easier attacking the network and violating the privacy of users.The most important factor affecting the performance and security of Tor is how selecting a path... 

Different data sources are creating a huge amount of data at increasing speeds that require real-time processing. Such data is called “Big data stream". Although, mining and analysis this type of data is so useful for companies, but it also may cause many privacy breaches. The principle issues for big data stream’ anonymization are real time processing and information loss. There are some works that are proposed for data streams, but they have some drawbacks such as inefficient anonymization of big data stream and also not consider time expiration of tuples that lead to increase the information loss and cost of the data publishing. In this thesis, in order to speed up the ability of big data... 

In recent two decades, different anonymous communication systems has been proposed. These systems are interested by journalists, bank employees, military forces, and human rights advocates. Tor is one of the most popular anonymous communication systems. Tor uses onion routing for privacy preserving. Re-cently, many attacks has been introduced against the anonymity of Tor users.In these attacks entry and exit nodes are compromised. One of these malicious nodes, makes the attack on the intented flow and the other one recognizes the flow. All these attacks admit their vulnerability against dummy messages. They state that, because of dynamics of onion’s keys, any dummy injection will dis-turb... 

In today's world in which a major part of information is digitalized and a large portion of the communication is done via computer networks, entities authentication while maintaining privacy is a concern with the growing importance and value. To meet this goal, during the past two decades, anonymous authentication protocols with different approaches for use in various applications has presented and developed. These protocols enable users to authenticate based on some of their properties, without revealing their own identities. Secret handshake protocols are considered as type of anonymous authentication protocols. This protocol has the unique feature of hiding users' affiliation to the... 

Social networks and the shared data in these networks are always considered as good opportunities in hands of the attackers. To evaluate the privacy risks in these networks and challenge the anonymization techniques, several de-anonymization attacks have been introduced so far. In this thesis, we propose a technique to improve the success rate of passive seed based de-anonymization attacks. Our proposed technique is simple and can be applied in combination with different types of de-anonymization attacks. We show that it can achieve high success rates with low number of seeds compared to similar attacks. Our technique can also be used for applying partial attacks on graphs which results in... 

Applied pi calculus is a variant of the pi calculus with extensions for modeling cryptographic protocols. In such a calculus, the security guarantees are usually stated as equivalences. While process calculi provide a natural means to describe the protocols themselves, epistemic logics are often better suited for expressing certain security properties such as secrecy and anonymity. These methods studied in this work to investigation the verification of privacy properties in security protocols. And finally, a new approach is introduced to bridge the gap between these two approaches: using the set of traces generated by a process as models. In this method an epistemic logic has constructs for... 

Mobile localization development, is the reason for appearance of location-based services (LBS). Be sure of not disclosing the user personal information is the main challenge in LBS. Many different concepts and approaches for the protection of location privacy have been described in the literature which change the query of user to server. These approaches falling roughly into two main categories: centralized and distributed (user-centric). Centralized category includes approaches like “changing query pattern” using encryption on user device, or using an “anonymizer trusted third party”. In such approaches threat of an untrustworthy LBS server is addressed by the introduction of a new... 

Anonymity helps in preserving user’s privacy in communication networks. In this respect many protocols with different characteristics have been proposed, as yet. Beside these protocols there have been introduced a lot of attacks, in which the ultimate goal is reducing the degree of provided anonymity. There is a class of attacks, where attacker tries to relate users of anonymity system to each other, just by observing execution of protocol. There is no need to compromise system’s nodes or even manipulating sent or received messages. Here, the attacker omits internal mechanism of protocol and assumes it has no vulnerability. The Statistical Disclosure Attack (SDA) is one of these attacks.... 

One of the biggest challenges in online communication is privacy of individuals. Although anonymous communication (AC) protocols has been the subject of several security and anonymity analyses recently, there are still few frameworks for analyzing such complex systems (e.g. Tor) and their anonymity properties in a unified manner. In this study, an overview of anonymity features and techniques will be discussed by examining various protocols that provide undetectable network communication. Afterwards, the Tor network is described more precisely. Furthermore, the literature of formal methods is briefly reviewed, and the Universal Composable (UC) framework for the analysis of cryptography...