| Many security services, such as authentication and key management, rely on trusted third parties (TTPs) which provide a common root of trust, thereby enabling secure communication among all users. However, in many applications it is impractical to assume universally trusted TTPs. A broad class of such applications involves ad hoe groups, which include peer-to-peer systems (P2P), and mobile ad hoc networks (MANETs). Another class of applications which can benefit from avoidance of a single centrally trusted TTP are critical online services, such as certification, revocation and time-stamping. Centralized operation of such security services is undesirable because it leads to a single point of failure.; The security needs of both ad hoc groups and the critical online services motivate research on decentralized security services. This thesis investigates three decentralized security services: (1) Establishment of secure communication between two human-operated devices, without relying upon a TTP, (2) Distributed digital signature schemes that enable any set of t + 1 group members to sign messages on behalf of the group, even in the presence of at most t faulty members, and (3) Secure membership management and secure communication in ad hoc groups.; The main research contributions of this thesis can be summarized as follows:; We show how to establish secure communication two devices over a short-range wireless communication channel, using messages that are visually authenticated by the users of these devices.; We also present a novel provably secure cryptographic protocol for establishing security between devices connected with a low-bandwidth (e.g. 20-bits) authenticated channel, e.g., the visually authenticated channel in the above application.; Next, we focus upon distributed RSA signature schemes. We present a practical key-recover attack on a recently proposed distributed (proactive) RSA signature scheme [LL00].; Finally, we turn our attention to secure membership management and secure communication in ad hoc groups. Firstly, we propose an efficient protocol to securely extend an ad hoc group in a distributed manner. Compared to prior proposals [KZL+01, KLX+02, LZK+02, NTY03], our protocol has minimal communication requirements, namely a single round of asynchronous communication. Secondly, we present a scheme to speed-up secure communication in ad hoc groups. (Abstract shortened by UMI.)... |
