Subject: RE: Deriving a symmetric key from the DH key

From: "Paul Leach" <[email-masked]>
Date: Tue, 19 Oct 2004 10:56:10 -0700

Following up on my earlier post:

Since there's no hash in kcrypto suites, and get_mic isn't a hash, and
we need one to derive keys in PKINIT, and PKINIT is supposed to be
crypto agnostic, that seems to imply strongly that we must define the
hashes (or, more generally the key derivation function) and hash-ids in
an extensible and negotiable way in PKINIT.

Or, add hashes to kcrypto suites.

> -----Original Message-----
> From: Paul Leach
> Sent: Tuesday, October 19, 2004 10:48 AM
> To: Liqiang(Larry) Zhu; [email-masked]; [email-masked]
> Subject: RE: Deriving a symmetric key from the DH key
> 
> No, I didn't agree with this. get_mic is not a hash. A hash may be
> embedded in its output, but the presence of other bits (such as
sequence
> numbers, version numbers, etc) is allowed and I believe common, and if
so
> makes it not suitable as a hash for creating keys.
>

---

From: Sam Hartman <[email-masked]>
Date: Tue, 19 Oct 2004 14:07:03 -0400

>>>>> "Paul" == Paul Leach <[email-masked]> writes:

    Paul> Following up on my earlier post: Since there's no hash in
    Paul> kcrypto suites, and get_mic isn't a hash, and we need one to
    Paul> derive keys in PKINIT, and PKINIT is supposed to be crypto
    Paul> agnostic, that seems to imply strongly that we must define
    Paul> the hashes (or, more generally the key derivation function)
    Paul> and hash-ids in an extensible and negotiable way in PKINIT.

Agreed.  I'll point out that at the same time we should negotiate the
hash used to authenticate the initial message.

    Paul> Or, add hashes to kcrypto suites.

I still think this is a bad idea.  There is a reasonable probability
that kcrypto will be published as an RFC before this could happen.

If we had a good candidate function for bitstring2random I'd agree
adding it to a future version of kcrypto would be desirable.  We
don't.  Hashes are the best thing we have; as far as I can tell we
have no particularly good basis for believing they do the job other
than prair and a need to have the job done.

--Sam