I had always assumed that PEM would one day support multiple publickey
cryptosystems. And that 1421 was designed for such an eventuality.
On preparing to privacy enhance a message to multiple recipients, of
course one must be prepared to determine the recipient's full
certification path prior to signing/encrypting, and therefore be in a position
to
determine their supported cryptosuite(s), and at least one supported PCA.
An originator is then quite likely to then be preparing multiple
Originator-IDs plus MIC-Info and supporting trust path for the
"Assymetric subset" of recipients, differentiated both on supported PCA
policies, and/or cryptosuite.
Your reply to Sandy asserted that the design only catered for the need
to separate key exchange procedures on a per-receipient basis for the
situation of mixed symemtric and assymmetric recipient capabilities.
How, literal was this statement or intent?
How realistic is my scenario of an originator processing, on a
per-message basis, alternative originator trust paths and (possibly)
signatures on a per-recipient basis based either on knowlege of the PCA
policies a recipient set is known to accept, or the cryptosuite used by
particular recipient set, or a mixture of these criteria?
When originating a mail to two exploders who, as recipients are in PCA
domains A & B, its necessary to originate the message with the
appropriate distinction between the trust paths used to support the
automatic authentication process in the asymmetric case.
A similar example would exist (logically) if each exploder is in a
separate asymmetric cryptosuite community.
Peter.