Re: open-pgp / s/mime interoperability

[pgut001@cs.auckland.ac.nz (Peter Gutmann)]

>: there is no reason why you can't have PGP
>: messages backed by X.509 certificates, and it is trivial to use S/MIME
>: with OpenPGP certificates.  I'm planning on writing a short
>: informational RFC on how to do it once we all get RFC numbers for our
>: respective systems.

>open-pgp public keys aren't based on X.509 keys, so I would've thought
>s/mime implementation would barf on them.  

Actually S/MIME *could* support the use of PGP keys, but there's a field
(the SubjectKeyIdentifier) missing from the CMS SignerInfo which prevents
this.  This is rather inconsistent, because the same field is present in
the RecipientInfo.  I'm currently arguing in favour of adding it to 
SignerInfo on the basis that any argument against it would also apply to
RecipientInfo.  Not sure whether it'll work though - a couple of list
members seem convinced that exactly the same thing which is currently in
RecipientInfo won't work if used in SignerInfo.

Peter.