Re: Notification authentication in CPIM

Graham Klyne <[email protected]> writes:

> BTW, why the concern with covert channels?
....

In secure applications, any unused and undisplayed free text headers
are open for use as covert channels.  For 'message/CPIM-PIDF' format
messages, the solution is simple, define the profile so that each
message contains exactly three headers, a 'From' header, a 'To'
header', and a 'DateTime' header.

This discussion reminds me to ask about 'Subject' headers in
CPIM-MSGFMT.  Where are they expected to be displayed?  Most IM
systems I've used display nothing but message content.  Note that in
secure applications, the content in every 'Subject' header must be
displayed.  The result would be visual clutter in a GUI.  On the other
hand, an application could simply reject messages with 'Subject'
headers.  In any event, what are they for, and what must every
application do with them?

The concern I just expressed about covert channels is probably valid for
applications with security requirements that are stronger than those
that need concern this working group.

John


  [reminder: [email protected] for non-technical discussions, please]