Subject: NSEC3 Issue 10: Potential DoS on Servers

From: Geoffrey Sisson <[email-masked]>
Date: Tue, 21 Feb 2006 18:27:15 GMT

Issue:

Significantly more work is required for a name server to respond to
queries which require negative proofs using NSEC3 than is required for
a client to compose and send them.  For each such query, the name
server must repeat the hash function for the number of iterations
specified in the NSEC3 RRs.  Consequently, name servers with NSEC3
zones are susceptible to asymmetric DoS attacks.

Resolution:

None at present.

If name servers serving NSEC3 zones were to have suitable hardware
acceleration for SHA-1, it's possible that the rate of queries required
to degrade server function could be made to be higher than that
required to saturate the server's network connection(s).

Also, while not optimal, implementations could provide a reduced
quality of service for queries which require negative proofs, so that
resolution and validation of existing names will not be compromised.

--
to unsubscribe send a message to [email-masked] with
the word 'unsubscribe' in a single line as the message text body.
archive: <http://ops.ietf.org/lists/namedroppers/>

---

From: Wes Hardaker <[email-masked]>
Date: Wed, 22 Feb 2006 14:46:40 -0800

>>>>> On Tue, 21 Feb 2006 18:27:15 GMT, Geoffrey Sisson <[email-masked]> said:

Geoffrey> Significantly more work is required for a name server to
Geoffrey> respond to queries which require negative proofs using NSEC3
Geoffrey> than is required for a client to compose and send them.

I suspect this has been discussed before and I simply missed it:  I
assume that the possibility of allowing sites to select between NSEC3
and NSEC has been discussed?  The downside, of course, is that you
can't drop NSEC and thus a higher complexity.  The upside is that zone
operators can pick their poison at least.

-- 
Wes Hardaker
Sparta, Inc.

---

From: Geoffrey Sisson <[email-masked]>
Date: Wed, 22 Feb 2006 23:53:22 +0000

> operators can pick their poison at least.

NSEC3 is not intended to replace NSEC, so zone operators may always
elect to use NSEC.

Geoff