In general, the hidden key method is not compatible with
applications which are based on the published public key method
because their databases typically do not store the <keysel>
field and moreover they are not designed with the security
protocols necessary to prevent the public key from being
exposed.
Jeff,
Your entire message is nonsense, as exemplified by this closing
paragraph. You are making assumptions about databases that are
completely outside the scope of the specifications.
The PEM/MIME database requirements are as follows:
1. an implementation must be able to access the public keys of
recipients in order to send encrypted messages.
2. an implementation must be able to access the private keys of the
originator in order to send signed messages.
Exactly how this is done and controlled is 100% at the discretion of the
implementor of the user's application. This is precisely the same as it
was in RFC 1421 and we saw no need to change it.
Jim