We undertook a project to secure the distribution of medical information using Wax. This is a proprietary hypertext-based system used for information such as treatment protocols, drug formularies, and teaching material. An initial attempt, using digital signatures (in line with a recent European standard) and certificates conforming to X.509 has thrown up a number of interesting problems with current approaches to public key infrastructures. While the X.509 philosophy may be suitable for many

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... ectronic commerce applications, signatures on which we may have to rely for many years -such as those on books and contractsappear to require a different approach.