Re: [lamps] CMS: selection of key management technique to use for EnvelopedData

[Russ Housley <[e-mail]>]

David:

> Since neither the original CMS RFC 5652 nor its update mention the topic how to select the key management technique to use, 
> the questions remains: was this on purpose?
> If not, I'd say this an omission to be sorted out.
> If yes, I'd expect some reasoning why, and a concrete pointer to, e.g., some other RFC (maybe, on specific uses like S/MIME) where concrete guidance is given.
I am sure you know this, but they can be mixed in the general case.  For example, one recipient could have a certificate with an RSA public key, and another recipient could have a certificate with an ECDH public key.  The sender would use KeyTransRecipientInfo for the first one, and the sender would use KeyAgreeRecipientInfo for the other one.  For this reason, I am not sure what guidance would be added to CMS.

RFC 2630 was published in June 1999.  This was the first version of CMS that included more that one flavor of RecipientInfo.  In the 20+ years since RFC 2630 was published, this is the first time that this has been a concern.  If an implementation supports a particular public key type (identified by the subjectPublicKeyInfo.algorithm in the certificate), then the implementation should "know" whether it is a key transport or a key agreement algorithm.  If the algorithm identifier is unknown or unsupported, then the implementation will throw an error.

Russ