ietf-smime
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Re: Selecting key-management algorithm...

1999-02-19 12:48:32
Ephemeral-Static Diffie-Hellman is the mandatory to implement algorithm to
ensure interoperability.  Since Ephemeral-Static Diffie-Hellman is a key
agreement algorithm, that is the mandatory to implement portion of the
protocol.

Russ


At 03:08 PM 2/18/99 +0000, Hilton Day wrote:
Hi all,

What (if anything) denotes whether a CMS message should use KA or KT as the
key-management algorithm?

I've looked through the spec, and can't see anything which mandates a method 
for
doing this, so I can only assume it is an implementation-specific choice (i.e.
User-input, or the programmers decide when writing the mail client, based on
security policy).

This leaves me wondering why KA is a "must" for the CMS - it is conveivable 
that
KA would never be used within the context of S/MIME, as mail clients could 
simply
use KT to wrap their CEK's.

Ok - I realise that in the interests of interoperability, KA should be 
implemented
in order that a recipient can read a mail sent with a shared-secret-based 
key, but
in the same way as Symmetric Key-Encryption Key algorithms are a "may", surely
this is something for the implementor to decide?

I realise that, as I've only been following the spec. since CMS-09, I've 
probably
already missed conversations along these lines, in which case, apologies
to all
those who've hashed over this - but I'd appreciate an explanation.. :-)

Thanks,

Hilton.

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