Re: [dnssd] Confirming consensus from DNSSD Privacy discussion in Bangkok

Christian Huitema <huitema@huitema.net> Thu, 15 November 2018 02:35 UTC

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Date: Wed, 14 Nov 2018 18:34:51 -0800
Cc: David Schinazi <dschinazi.ietf@gmail.com>, dnssd@ietf.org
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Subject: Re: [dnssd] Confirming consensus from DNSSD Privacy discussion in Bangkok
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> On Nov 14, 2018, at 5:55 PM, Christopher Wood <christopherwood07@gmail.com> wrote:
> 
> One issue Christian and I discussed after the meeting concluded is the
> possibility of dictionary attacks on the service identifier. With the
> predictable nonce obfuscation proposal, which would necessarily
> include the service identifier in the first query, leaking the client
> public key to an adversary allows offline dictionary attacks on the
> service. Whether or not this is a problem depends on the threat model.

I agree this id an attack, but it is a secondary exploit of leaking the key. My take is that leaking the key is a catastrophic failure, which enables tracking the key's owner movements. Leaking the service ID on top of the user identity is not good, but service connections can also be identified by various fingerprinting methods. If you are paranoid, use a two stage method. But in most cases, the trade off between risk and performance will favors the one stage approach.


> 
> Note that it's likely possible to bootstrap the two-stage approach
> using the single-stage approach. But that would bring back in the
> question of whether or not to use TLS.

I would personally rather use TLS than invent something, but Bob's draft is probably fine too.

-- Christian Huitema