Subject: call for consensus: GSSAPI TKEY exchange and TSIG RFC

From: Ólafur Gudmundsson/DNSEXT co-chair <[email-masked]>
Date: Tue, 06 Aug 2002 23:07:41 -0400

Levon Esibov, (principal author of GSSAPI TSIG) asked for further
working group input on the issue raised about 10 days ago.
GSSAPI TSIG ID has passed working group last call,
in this document there is a issue in one section related to
the key exchange interaction that is in violation to the TSIG RFC.
In section 4.2 of RFC 2845:
"The server MUST not generate a signed response to an unsigned request."

In GSSAPI TSIG ID the TKEY sequence specifies that the server can sign the
last message in order to enable the client to make sure the exchange was
successful.

In general it is a bad idea to allow extensions to a protocol to modify
the base protocol in a non explicit manner.

In this case there are following advantages:
	certain value to the last TSIG from security perspective, 	
	no client that is not GSSAPI TSIG participant will see this
	compliant with deployed base from at least 2 vendors.

And following drawbacks:
	This is a violation with minimal gain and may force change in TSIG
		processing in existing implementations due to the fact
		that there is no secret known until after the message is 		processed.

In general TKEY exchanges for all algorithms can derive the same
benefits from the behavior specified in GSSAPI TSIG ID.
	
I have been asked to ask the working group if the following change to
TSIG RFC is acceptable:

In section 4.2 of RFC 2845 replace:
"The server MUST not generate a signed response to an unsigned request."

With something like:
"The server MUST not generate a signed response to an unsigned request,
except if specification of an individual signature algorithm explicitly
allows this."

If this change is not acceptable or feasible, I will ask for guidance
from the working group how to best change the GSSAPI TSIG specification.
Please send me or the mailing list technical arguments for or against,
of particular interest is the effect of this change on existing TSIG
implementations.

	Olafur

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