Rivest and Lampson have recently introduced SDSI, a Simple Distributed Security Infrastructure. One of the important innovations of SDSI is the use of linked local name spaces. This paper suggests a logical explanation of SDSI's local name spaces, as a complement to the operational explanation given in the SDSI definition.

The Terminodes project is designing a wide area, mobile ad-hoc network, which is meant to be used in a public environment; in our approach, the network is run by users themselves. We give a global description of the building blocks used by the basic operation of the network; they all rely on various concepts of self-organization. Routing uses a combination of geography-based information and local, MANET-like protocols. Terminode positioning is obtained either by GPS, or by a relative positioning method. Mobility management uses self-organized virtual regions. Terminodes employ a form of virtual money called "nuglets" as an incentive to collaborate. Lastly, we discuss directions for providing some level of security.

This paper investigates the role of trust metrics in attack-resistant public key certification. We present an analytical framework for understanding the effectiveness of trust metrics in resisting attacks, including a characterization of the space of possible attacks. Within this framework, we establish the theoretical best case for a trust metric. Finally, we present a practical trust metric based on network flow that meets this theoretical bound. independent sources of certification, and rejects (by assigning low trust values) assertions with insufficient certification. The previous work raises many questions, including: To which kinds of attack is a trust metric resistant? Which trust metric is best? How well do these trust metrics work? 1

Semantic Web endeavors have mainly focused on issues pertaining to knowledge representation and ontology design. However, besides understanding information metadata stated by subjects, knowing about their credibility becomes equally crucial. Hence, trust and trust metrics, conceived as computational means to evaluate trust relationships between individuals, come into play. Our major contributions to Semantic Web trust management through this paper are twofold. First, we introduce our classification scheme for trust metrics along various axes and discuss advantages and drawbacks of existing approaches for Semantic Web scenarios. Hereby, we will devise our advocacy for local group trust metrics, guiding us to the second part which presents Appleseed, our novel proposal for local group trust computation. Compelling in its simplicity, Appleseed borrows many ideas from spreading activation models in psychology and relates their concepts to trust evaluation in an intuitive fashion.

Authentication of communication channels between devices that lack any previous association is an challenging problem. It has been considered in many contexts and in various flavors, most recently, by McCune et al., where human-assisted device authentication is achieved through the use of photo cameras (present in some cellphones) and 2-dimensional barcodes. Their proposed Seeing-is-Believing system allows users with devices equipped with cameras to use the visual channel for authentication of unfamiliar devices, so as to defeat man-inthe-middle attacks. In this paper, we investigate an alternative and complementary approach—the use of the audio channel for humanassisted authentication of previously un-associated devices. Our motivation is three-fold: (1) many personal devices are not equipped with cameras or scanners, (2) some human users are visually impaired (hence, cannot be in the authentication pipeline of a vision-based system), and (3) some usage scenarios preclude either taking a sufficiently clear picture and/or the use of barcodes. We develop and evaluate a system we call Loud-and-Clear (L&C) authentication, which, like Seeing-is-Believing, places little demand on the human user. The L&C system is based on the use of a text-to-speech engine to read an auditoriallyrobust, grammatically-correct pass-phrase derived from an authentication string that is to be used by peer devices. In particular, by coupling the auditory reading of the one-way hash of an authentication string on one device with the display of of this text on another device, we demonstrate that L&C is suitable for secure device pairing (e.g., key exchange) and similar tasks. We also describe several use cases, as well as provide some performance data for a prototype implementation and a discussion of the security properties of L&C. 1

Open networks allow users to communicate without any prior arrangements such as contractual agreement or organisation membership. However, the very nature of open networks makes authenticity difficult to verify. We show that authentication can not be based on public key certificates alone, but also needs to include the binding between the key used for certification and it's owner, as well as the trust relationships between users. We develop a simple algebra around these elements and describe how it can be used to compute measures of authenticity.

Contrary to the common belief that mobility makes security more difficult to achieve, we show that node mobility can, in fact, be useful to provide security in ad hoc networks. We propose a technique in which security associations between nodes are established, when they are in the vicinity of each other, by exchanging appropriate cryptographic material. We show that this technique is generic, by explaining its application to fully self-organized ad hoc networks and to ad hoc networks placed under an (off-line) authority. We also propose an extension of this basic mechanism, in which a security association can be established with the help of a "friend". We show that our mechanism can work in any network configuration and that the time necessary to set up the security associations is strongly influenced by several factors, including the size of the deployment area, the mobility patterns, and the number of friends; we provide a detailed investigation of this influence.

Authentication using a path of trusted intermediaries, each able to authenticate the next in the path, is a well-known technique for authenticating entities in a large-scale system. Recent work has extended this technique to include multiple paths in an effort to bolster authentication, but the success of this approach may be unclear in the face of intersecting paths, ambiguities in the meaning of certificates, and interdependencies in the use of different keys. Thus, several authors have proposed metrics to evaluate the confidence afforded by a set of paths. In this paper we develop a set of guiding principles for the design of such metrics. We motivate our principles by showing how previous approaches failed with respect to these priniciples and what the consequences to authentication might be. We then propose a new metric that appears to meet our principles, and so to be a satisfactory metric of authentication.

SSH is designed to provide a secure channel between two hosts. Despite the encryption and authentication mechanisms it uses, SSH has two weakness: First, the transmitted packets are padded only to an eight-byte boundary (if a block cipher is in use), which reveals the approximate size of the original data. Second, in interactive mode, every individual keystroke that a user types is sent to the remote machine in a separate IP packet immediately after the key is pressed, which leaks the interkeystroke timing information of users' typing. In this paper, we show how these seemingly minor weaknesses result in serious security risks.

: We introduce Delegation Logic (DL), a logic-based knowledge representation (i.e., language) that deals with authorization in large-scale, open, distributed systems. Of central importance in any system for deciding whether requests should be authorized in such a system are delegation of authority, negation of authority, and conflicts between authorities. DL's approach to these issues and to the interplay among them borrows from previous work on delegation and trust management in the computer-security literature and previous work on negation and conflict handling in the logic-programming and non-monotonic reasoning literature, but it departs from previous work in some crucial ways. In this introductory paper, we present the syntax and semantics of DL and explain our novel design choices. This first paper focuses on delegation, including explicit treatment of delegation depth and delegation to complex principals; a forthcoming companion paper focuses on negation. Compared to previous lo...