Lee and Yeh recently presented a delegation-based authentication protocol for portable communication systems (PCSs), which is claimed to provide non-repudiation in on-line authentication. This investigation indicates that their protocol has a weakness in that a malicious visited location register can forge the authentication messages in off-line authentication processes, preventing mobile users from obtaining non-repudiation in such processes. This study also presents an enhanced protocol, which not only has the same security properties as the original protocol but also avoids the weakness in the original scheme and reduces the computational cost.

The star graph interconnection network has been recognized as an attractive alternative to the hypercube network. Previously, the star graph has been shown to contain a Hamiltonian cycle. In this paper, we consider an injured star graph with some faulty links and nodes. We show that even with f/sub e//spl les/n-3 faulty links, a Hamiltonian cycle still can be found in an n-star, and that with f/sub v//spl les/n-3 faulty nodes, a ring containing at most 4f/sub v/ nodes less than that in a Hamiltonian cycle can be found (i.e. the ring contains at least n!-4f/sub v/ nodes). In general, in an n-star with f/sub e/ faulty links and f/sub v/ faulty nodes, where f/sub e/+f/sub v//spl les/n-3, our embedding is able to establish a ring containing at least n!-4f/sub v/ nodes.