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added a section for the discussion of privacy problem mitigation tech… #4

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May 24, 2016
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added a section for the discussion of privacy problem mitigation tech… #4

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49 changes: 49 additions & 0 deletions draft-huitema-dnssd-privacy.xml
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Expand Up @@ -645,6 +645,55 @@ instance discovery key

</section>


<section title="My Thoughts on Privacy Problem Mitigation Techniques">
<t>
A problem with the mitigation techniques described so far is the need for a pairing.
When service instance keys are used, each service instance needs a separate key,
which in turn has to be transmitted to all devices that should be able to
discover the corresponding service instance.
This is disadvantageous in two ways.
On the one hand, it demands a pairing for each service instance;
on the other hand it makes it impossible to discover new service instances without prior pairing.
Both problems can be mitigated by using the method described in the following.
</t>
<t>
Privacy Preserving Service Discovery can be divided into three (independent) layers.
</t>
<t>
<list style="symbols">
<t>
Device Pairing: In this step users pair their devices.
There are two kinds of pairings: (1) intra-user pairing, which
is a pairing of devices of the same user; this can be done
without any configuration by a meta-service (pairing data synchronization service) in
a trusted (home) network;
(2) inter-user pairing is a pairing between devices of "friends".
Since this has to be done manually - e.g. by verifying a fingerprint leveraging QR-Codes -
it is important to limit it to once per pair of friends.
</t>
<t>
Directory Discovery: The set of devices that offer service instances can be seen as a distributed service directory.
When a user wants to discover services, she first discovers the part of the service directory she is authorized to use,
meaning the devices of her online friends.
This is done using an other meta service (private service directory service, PSDS) whose task it is to handle queries for actual services.
The connection to this service is done using private mutual authentication guaranteeing the privacy of both parties.
</t>
<t>
Service Querying: The PSDS is offered by a small DNS server running on each user's device that can be queried for the service instances offered by the
corresponding user.
</t>
</list>
</t>
<t>
This mitigates both afore mentioned problems as it reduces pairing to one pairing per pair of friends and allows to offer services in
a privacy preserving way whose existence was unknown at the time of pairing.
This grants an almost zeroconf user experience.
</t>
</section>



<section title="Security Considerations">
<t>
This document specifies a method to protect the privacy of
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