Greg,
John Linn and Steve Kent covered the right points. We've had some
discussion internally here about merging MIME and PEM. If MIME were
prevalent, it would make a lot of sense for the PEM specs to depend on
MIME and for the two to be intertwined. Since MIME is not yet
prevalent, it's inappropriate to depend on it, and the PEM specs are
moving forward without MIME.
It's probably obvious that MIME would benefit from -- and could easily
accommodate -- PEM. It turns out that MIME would be beneficial to
PEM. The PEM specs provide for multiple enhanced sections within a
single message. One gnawing detail is there isn't a completely
satisfactory way to distinguish which sections are to be (on the
sending side) or were (on the receiving side) enhanced. Any
conventions established for this purpose are really a poor man's
reinvention of the same problem MIME solves more completely. As a
consequence, most implementations of PEM will probably support only
one enhanced section per message. This limitation would be less
likely in a MIME environment, so even from a purely PEM perspective,
the merge of MIME and PEM provides increased functionality.
I expect merged MIME and PEM implementations will appear quickly and
naturally. However, until most mail users use MIME, PEM can't be tied
to MIME completely.
Steve