RE: [dhcwg] Re: DHCID and the use of MD5 [Re: Last Call:'Resolution of FQDN Conflicts among DHCP Clients' to Proposed Standard]

[Jeffrey Hutzelman <jhutz at cmu.edu>]

On Thursday, December 01, 2005 08:48:10 AM -0500 "Bernie Volz (volz)" 
<volz at cisco.com> wrote:

> How about we address issue 1 by expanding the DHCID RR type code. We
> have 16-bits and we're just using 4 values presently. There's plenty of
> room for future expansion *SHOULD* someone come along and demand a new
> algorithm in the future. I can't see why this would EVER occur since
> this really isn't about strong cryptographic protection (we're just
> trying to make it non-trivial to find a client's identity by not storing
> it in clear text).

I think that's a good start; in fact, I was going to propose something very 
similar.  This solves half the problem; particularly, it makes it possible 
to indicate that some other hash is in use.  It does bind the hash to the 
type, rather than allowing them to be specified orthogonally, but I don't 
think that's a major problem.  If it ever becomes an issue, there should be 
no problem defining a type where the next 16 bits indicate a subtype and 
the 16 bits after that indicate a hash.

However, it doesn't solve the other half of the problem, which is present 
even without considering changing hash algorithms.  The problem is that for 
any given fqdn and DHCP client, there are multiple possible DHCID RR's; in 
particular, one for each type.  In order the update mechanism to work 
without requiring either an advance query or multiple update attempts, all 
possible updaters must agree in advance on the type in use.  This lack of 
negotiation seems problematic to me, even in the absence of multiple hash 
algorithms.

-- Jeffrey T. Hutzelman (N3NHS) <jhutz+ at cmu.edu>
  Sr. Research Systems Programmer
  School of Computer Science - Research Computing Facility
  Carnegie Mellon University - Pittsburgh, PA


_______________________________________________
Ietf mailing list
Ietf at ietf.org
https://www1.ietf.org/mailman/listinfo/ietf