The Twenty-first International Workshop on Security Protocols will take place from Monday March 18th to Wednesday March 20th, 2013 at Sidney Sussex College, Cambridge, England.

As with previous years, attendance at the International Workshop on Security Protocols is by invitation only.

In order to be invited you must submit a position paper. You are therefore encouraged to consider submitting such a paper.

The theme of this year's workshop is "What's Happening on the Other Channel?"

Many protocols use a secondary channel, either explicitly (as in multichannel protocols) but more usually implicitly, for example to exchange master keys, or their hashes. The role of the Other Channel is fundamental, and often problematic, and yet protocol composers typically take them as a given.

Sometimes the Other Channel really is completely covert, but sometimes it just has properties that are different. And it's not only security properties that are relevant here: bandwidth, latency and error rate are often important considerations too. Even a line-of-sight channel usually doesn't quite have the properties that we unthinkingly attributed to it.

Moriarty has been subscribing to the Other Channel for years: perhaps it's time for Alice and Bob to tune in too.

The theme itself is not intended to restrict the topic of your paper, but to help provide a particular perspective and to focus the discussions. Our intention is to stimulate discussion likely to lead to conceptual advances, or to promising new lines of investigation, rather than merely to consider finished work.

Pre-proceedings will be provided at the workshop. The proceedings of previous workshops in this series have been published by Springer-Verlag as Lecture Notes in Computer Science (see LNCS 7114, 6615, 5964, 5087, 4631, 3957, 3364, 2845, 2467, 2133, 1796, 1550, 1361 and 1189). If you have not previously attended the Security Protocols Workshop, you may find it helpful to refer to these to get an idea of the flavour.

To be considered for invitation, you must send a first draft of a position paper to James Malcolm (j.a.malcolm@herts.ac.uk) by the deadline noted above. If you wish, you may make an initial response to say that you are potentially interested.

Feel free to circulate this invitation widely, but do remember that the workshop has a limited size and in order to be invited you must submit a position paper. A printable copy of this announcement may be found at http://spw.stca.herts.ac.uk/Advertisement2013.pdf.

If you are invited to the workshop, don't forget to send us a revised copy of your paper (for inclusion in the pre-proceedings) by the deadline above. You should also register using the form that will be provided.

If you have any enquiries about the workshop then you might want to look on the web-site, but if your question is not answered there, please contact one of the organizing committee:

Bruce Christianson (Email: B.Christianson AT herts.ac.uk) Professor of Informatics, University of Hertfordshire

James A. Malcolm (Email: J.A.Malcolm AT herts.ac.uk, Tel: +44-1707-284310).

Frank Stajano (University of Cambridge)

Jonathan Anderson (University of Cambridge)