Bob,
Your remarks on compression are quite correct; encrypted texts, by definition,
cannot be compressed. However, the standardization of comprtession is well
known mine field. There are even more patents around than in cryptography.
I would think that the integration of security with MIME would precisely allow
us to incorporate compression in a flexible way, when needed and if needed. It
is natural to define a "compressed text" content type (or maybe a compressed
text encoding type). Once this content is described, then it can be carried as
an encrypted mime part.
Christian Huitema