The systematic study of security protocols started, as far as the public literature is concerned, almost 20 years ago. A paper by M. D. Schroeder and the present writer [1] may be taken as a specimen; it was written in 1977 and published in 1978. it was, of course, written against the background of the technology of the time and made various assumptions about the organizational context in which its techniques would be used. The substantial research literature that has since appeared has, by and large, made similar assumptions about the technological and organizational environments. Those environments have in Fact changed very considerably, and the purpose of the present note is to consider whether the changes should affect our approach to security problems. it turns out that where confidentiality is concerned, as distinct from authenticity and integrity, there is indeed a new range of options.
