Re: Compound authentication "issue"

["Nystrom, Magnus" <mnystrom@xxxxxxxxxxxxxxx>]

I believe you are right Lawrence. In essence, the client's response is a
keyed hash of a string of which the digest-uri-value is a part. Since the
MITM cannot influence that part, the "sacred" serv-type won't be present
when a MITM is active and the true SACRED server won't therefore accept
the response (it must not mechanically take the client-provided cleartext
digest-uri-value and use that when calculating its version of the response
though, but also check that the serv-type IS "sacred" and the name is its
own).

Assuming this holds I agree, some text in the Security Considerations
section seems to be sufficient.

Thanks,
-- Magnus

On Wed, 27 Nov 2002, Lawrence Greenfield wrote:

>
> Upon further consideration, isn't the man-in-the-middle attack
> thwarted by the inclusion of "digest-uri-value" in the hash?
>
> The DIGEST-MD5 client hash includes a client-selected
> "digest-uri-value" which in sacred's case will be "sacred/<host>". In
> a MITM attack, those values will be something else.
>
> A MITM attack as described in the WG meeting is thwarted because
> digest-uri-value wouldn't match what the sacred server is expecting.
>
> If it would make people feel better, we can mention this safeguard in
> the security considerations section.
>
> Larry
>