The Subset Difference Rekeying (SDR) method [8] is the most efficient stateless group rekeying method proposed in the literature. We study two important issues related to the SDR method. First, we address the issue of reliable rekey transport for SDR. We present a key distribution scheme, called FEC-BKR, that enables members to receive the current group key in a reliable and timely fashion despite packet losses in the network. Through simulation, we show that in most scenarios, FEC-BKR outperforms previously proposed schemes for reliable rekey transport. Second, we address the issue of self-healing key distribution for SDR. We present a group key recovery scheme that adds the self-healing property to SDR, i.e., our scheme enables a member that has missed up to a certain number m of previous rekey operations to recover the missing group keys without asking the key server for retransmission. The additional communication overhead imposed by our key recovery scheme is quite small (less than 3m additional keys).

We consider the broadcast encryption problem where one sender wishes to transmit messages securely to a selected set of receivers using a broadcast channel, as is the case in digital television for example. Specifically, we study the subset difference scheme for broadcast encryption and the number of broadcast transmissions required when using this scheme. The effects of adjacency in the user set are considered and we introduce the notion of transitions in the user set as a means to quantify the adjacency. We present upper and lower bounds for the number of transmissions based on the number of transitions between privileged and nonprivileged users in the user set. For cases where the privileged users are gathered in a few groups we derive the maximum number of transmissions.

Abstract — Position-based routing protocols make routing decisions based on the geographical position of the destination of a packet. Such protocols scale well since they do not require nodes to maintain explicit routes. Instead each node must know only its own position, the position of its neighbors, and the position of the destination. Thus, a critical component of position-based routing protocols is the position service that allows nodes to obtain the position of a destination node. In this paper we analyze the security vulnerabilities of positionbased routing protocols and virtual home region (VHR)-based distributed position service systems. We propose methods to protect the position information from both external and internal attackers. We then discuss and propose several mitigation mechanisms against position abuse by internal attackers that exploit the position service to trace their targets. Finally, we propose a position verification mechanism that allows the position service to verify that the positions reported by nodes are correct. I.

encryption

Subset Difference Revocation (SDR) [8] has been proposed to perform group rekeying in a stateless manner. However, statelessness comes at a cost in terms of storage and message overhead when the number of currently active members is much smaller than the number of potential group members [3]. We propose a dynamic SDR scheme to address these problems. Rather than maintaining a large static key tree that accommodates all potential group members, we use a smaller dynamic key tree for only currently active members. We dynamically assign current members to the positions in the key tree rather than using fixed pre-assignment. The smaller key tree requires less storage and dynamic assignment achieves a smaller rekeying cost. Our evaluation shows that the dynamic scheme significantly improves the performance of SDR, reducing by half the rekey communication cost in the case that the number of the currently active members is much less than the total number of potential members. Compared to SDR in [8], dynamic SDR does not need to know the maximum number of potential group members in advance, a value that can be difficult to estimate in practice.

We consider the broadcast encryption problem where one sender wishes to transmit messages securely to a selected set of receivers using a broadcast channel, as is the case in digital television for example. Specifically, we study the subset difference scheme for broadcast encryption and the number of broadcast transmissions required when using this scheme. The effects of adjacency in the user set are considered and we introduce the notion of transitions in the user set as a means to quantify the adjacency. We present upper and lower bounds for the number of transmissions based on the number of transitions between privileged and nonprivileged users in the user set. For cases where the privileged users are gathered in a few groups we derive the maximum number of transmissions.