Nonmonotonic Trust Management for P2P Applications

Community decisions about access control in virtual communities are non-monotonic in nature. This means that they cannot be expressed in current, monotonic trust management languages such as the family of Role Based Trust Management languages (RT). To solve this problem we propose RT-, which adds a restricted form of negation to the standard RT language, thus admitting a controlled form of non-monotonicity. The semantics of RT- is discussed and presented in terms of the well-founded semantics for Logic Programs. Finally we discuss how chain discovery can be accomplished for RT-.Comment: This paper appears in the proceedings of the 1st International Workshop on Security and Trust Management (STM 2005). To appear in ENTC

Knowledge Flow Analysis for Security Protocols

Knowledge flow analysis offers a simple and flexible way to find flaws in security protocols. A protocol is described by a collection of rules constraining the propagation of knowledge amongst principals. Because this characterization corresponds closely to informal descriptions of protocols, it allows a succinct and natural formalization; because it abstracts away message ordering, and handles communications between principals and applications of cryptographic primitives uniformly, it is readily represented in a standard logic. A generic framework in the Alloy modelling language is presented, and instantiated for two standard protocols, and a new key management scheme.Comment: 20 page

Believing the Integrity of a System (Invited Talk)

AbstractAn integrity policy defines the situations when modification of information is authorised and is enforced by the protection mechanisms of a system. Traditional models of protection tend to define integrity in terms of ad-hoc authorisation techniques whose effectiveness are justified more on the basis of experience and "best practice" rather than on any theoretical foundation. In a complex application system it is possible that an integrity policy may have been incorrectly configured, or that the protection mechanisms are inadequate, resulting in an unexpected system compromise. This paper examines the meaning of integrity and and describes a simple belief logic approach for analysing the integrity of a system configuration

A Step towards a Solution to Information Privacy Problem on Online Social Networks

Online social networks, such as Facebook and Twitter, have gained popularity in recent years. With that popularity, come security problems, especially problems with information privacy. This paper provides an overview of information privacy issues for online social networks. One way to solve this problem is to use cryptography. However, cryptography on online social networks has not been studied exclusively. Most works have been done on access control. The main issue with cryptography is the number of keys needed to encrypt and decrypt the information. The most obvious number of keys would be to use one key for every user in our group of friends. This is not needed or entirely true as we show here. This paper, therefore, gives an attempt to show that the number of keys needed to achieve secure sharing among friends can in fact be much smaller than the number of friends. The number of keys can actually be reduced by approximately 500% on average, using the method presented here. We also provide proofs of correctness and security to confirm our claim

Modeling Adversaries in a Logic for Security Protocol Analysis

Logics for security protocol analysis require the formalization of an adversary model that specifies the capabilities of adversaries. A common model is the Dolev-Yao model, which considers only adversaries that can compose and replay messages, and decipher them with known keys. The Dolev-Yao model is a useful abstraction, but it suffers from some drawbacks: it cannot handle the adversary knowing protocol-specific information, and it cannot handle probabilistic notions, such as the adversary attempting to guess the keys. We show how we can analyze security protocols under different adversary models by using a logic with a notion of algorithmic knowledge. Roughly speaking, adversaries are assumed to use algorithms to compute their knowledge; adversary capabilities are captured by suitable restrictions on the algorithms used. We show how we can model the standard Dolev-Yao adversary in this setting, and how we can capture more general capabilities including protocol-specific knowledge and guesses.Comment: 23 pages. A preliminary version appeared in the proceedings of FaSec'0

RFID ownership transfer with positive secrecy capacity channels

RFID ownership transfer protocols (OTPs) transfer tag ownership rights. Recently, there has been considerable interest in such protocols, however, guaranteeing privacy for symmetric-key settings without trusted third parties (TTPs) is a challenge still unresolved. In this paper, we address this issue and show that it can be solved by using channels with positive secrecy capacity. We implement these channels with noisy tags and provide practical values, thus proving that perfect secrecy is theoretically possible. We then define a communication model that captures spatiotemporal events and describe a first example of symmetric-key based OTP that: (i) is formally secure in the proposed communication model and (ii) achieves privacy with a noisy tag wiretap channel without TTPs