Problem with use of NotUnderstood in negotiations

[Bill Studenmund <wrstuden@wasabisystems.com>]

I encountered a problem with how draft 15 specifies using NotUnderstood as
a reply to keys that aren't understood. Namely if something injects
garbage into the negotiation stream we can end up with a key BOTH sides
don't understand, and so they both sit there sending "foo=NotUnderstood"
back and forth to each other.

Yes, well-behaved negotiators won't offer a key they don't understand. But
the data stream can be corrupted, and all it would take is a single-bit
error in a key name and we encounter the above.

I propose we change the text to:

Any key not understood by the acceptor may be ignored by the acceptor
without affecting the basic function. However, unless the value for the
key was "NotUnderstood", the answer for a key not understood MUST be
key=NotUnderstood. If the value for the key was "NotUnderstood", the
acceptor MUST not answer the key.

Note: I can easily see closing the connection with an error in the above
case too.

Thoughts?

Take care,

Bill