In this paper, we present the Tree-List Certificate Validation (TLCV) scheme, which uses a novel tree-list structure to provide efficient certificate validation. Under this scheme, users in a public-key infrastructure (PKI) are partitioned into clusters and a separate blacklist of revoked certificates is maintained for each cluster. The validation proof for each cluster's blacklist comes in the form of a hash path and a digital signature, similar to that used in a Certificate Revocation Tree (CRT) [1]. A simple algorithm to derive an optimal number of clusters that minimizes the TLCV response size was described. The benefits and shortcomings of TLCV were examined. Simulations were carried out to compare TLCV against a few other schemes and the performance metrics that were examined include computational overhead, network bandwidth, overall user delay and storage overhead. In general, we find that TLCV performs relatively well against the other schemes in most aspects.

Consumer electronic devices, many of which short-range wireless enabled are becoming common. Such wireless devices need to connect to devices with which they might have no prior contact. These connections need to be managed by users who don't have much computer administration knowledge, where elaborate graphical user interfaces are unlikely and passwords cumbersome. In this paper, we explain Touch mediated Association Protocols (TAP), based on the intuitive concept of tapping. A simple computational device, the mediator, taps devices facilitating device discovery and secure key distribution. TAP is based on computationally cheap cryptography, doesn't need GUI or broadcasts for device discovery.

Providing effective certificate revocation status is an important yet burdensome aspect of PKI. It is widely assumed that certificate revocation lists (CRLs) [12] cannot provide bandwidth-efficient online certificate status. Using our reference delta CRL scheme, we show that this assumption is not true. Clients using reference delta CRLs never download complete CRLs -they construct revocation lists locally. Our scheme performs significantly better than any earlier CRL scheme and has comparable bandwidth performance with respect to OCSP [10].

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