[dns-operations] Announcement - DNS flag day on 2019-02-01

[Mark Andrews]

> On 14 Jun 2018, at 6:51 am, Florian Weimer <fw at deneb.enyo.de> wrote:
> 
> * Petr Špaček:
> 
>> you might be interested in information about "DNS flag day" coordinated 
>> by open-source DNS vendors and is planned for 2019-02-01
>> (February 1st 2019).
>> 
>> Further information can be found on
>> https://dnsflagday.net/
> 
> Is there still no reduction of EDNS buffer size to around 1200 bytes?
> Isn't it time after ten years to address that particular
> vulnerability?

If you are talking about fragmentation reassembly attacks you need to
use something with a cryptographic hash independent of EDNS.  TSIG with
a well known key and a 64 bit nonce in extra data of the TSIG record
would suffice.  One may be able to get away without the nonce but a
cryptographer would need to check if there is enough variability (time, id)
in the query without it.

e.g.
key name = “.”
key algorithm = “hmac-sha256”
key secret = all zeros.

For BIND 9 adding this to named.conf would allow named to answer such a client.
Named does not enforce that the extra data field is empty.  It just computes the
signature with the presented data.  Other implementations may vary.

key "." {
        algorithm hmac-sha256;
        secret "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=";
};

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-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742              INTERNET: marka at isc.org