The Append-Only Web Bulletin Board

A large number of papers on verifiable electronic voting that have appeared in the literature in recent years have relied heavily on the availability of an append-only web bulletin board. Despite this widespread requirement, however, the notion of an append-only web bulletin board remains somewhat vague, and no method of constructing such a bulletin board has been proposed. This paper fills the gap. We identify the required properties of an append-only web bulletin board, and introduce the concept of certified publishing of messages to the board. We show how such a board can be constructed in order to satisfy the properties we have identified. Finally, we consider how to extend the scheme to make the web bulletin board robust and able to offer assurance to writers of the inclusion of their messages. Although the work presented here has been inspired and motivated by the requirements of electronic voting systems, the web bulletin board is sufficiently general to allow use in other contexts.