Subject: Randomness requirements for message ID generation

From: Florian Weimer <[email-masked]>
Date: Tue, 12 Jul 2005 01:21:36 +0200

Apologies if this is the wrong forum to ask such questions.

What are the randomness requirements for message ID generation?  Are
simple time-dependent IDs acceptable?  What about PRNGs which leak
their internal state?  Would you recommend different levels of
randomness for stub and full resolvers?

(I know it's just a 16-bit number, so we aren't in a very good
position no matter what we do.  But there's no reason to make things
even worse, IMHO.)

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From: Eastlake III Donald-LDE008 <[email-masked]>
Date: Mon, 25 Jul 2005 15:00:16 -0400

I can't see the justification for a MUST. A SHOULD would be reasonable as it would mean that you need a good justification to do anything else.

If you want secure DNS transactions you have to use TSIG or SIG(0). 

Donald

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of David Conrad
Sent: Monday, July 25, 2005 1:37 PM
To: Edward Lewis
Cc: Ólafur Guðmundsson /DNSEXT co-chair; Florian Weimer; [email-masked]
Subject: Re: Randomness requirements for message ID generation

On Jul 25, 2005, at 10:12 AM, Edward Lewis wrote:
>> Good randomness should be used by all DNS resolvers on query ID.
...
> I know that this is a dead issue in the WG (fortunately), but I had 
> some real data to throw in.  And I wanted to kill once and for all the 
> notion that the message id had to be "random."

Hmm.  Perhaps this has been mentioned:

http://madchat.org/reseau/tcp-ip/tcpip-seqnb/#otherp

In terms of specification, I believe having query ids be as random as possible should be a MUST.  Anything else increases the likelihood of spoofability.

Rgds,
-drc

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From: Doug Barton <[email-masked]>
Date: Mon, 25 Jul 2005 16:02:50 -0700

The Purple Streak, Hilarie Orman wrote:

> The restriction to choose from the set of unused numbers should be
> mentioned explicitly in requirements ("drawing without replacement"),
> that will smooth out the distribution as the number of ids in
> use at any given time increases.

Would "drawing without replacement up to 1/N of the space" be better, for 
the right value of N?

Doug

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