[tor-dev] Using the HS protocol for unlinkability only

[Michael Rogers]

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Hi all,

(Please let me know if this belongs on tor-talk instead of here.)

I'm working on a messaging app that uses Tor hidden services to
provide unlinkability (from the point of view of a network observer)
between users and their contacts. Users know who their contacts are,
so we don't need mutual anonymity, just unlinkability.

I wonder whether we need everything that the Tor hidden service
protocol provides, or whether we might be able to save some bandwidth
(for clients and the Tor network) and improve performance by using
parts of the hidden service protocol in a different way.

First of all, we may not need to publish hidden service descriptors in
the HS directory, because we have a way for clients to exchange static
information such as HS public keys out-of-band.

Second, we may not need to use introduction points to protect services
from DoS attacks - we can assume that users trust their contacts not
to DoS them.

Third, we may be able to reduce the number of hops in the
client-service circuits, because we don't need mutual anonymity.

This isn't the first app to use hidden services for unlinkability, so
I expect this topic's come up before. Are there any discussions I
should look at before coming up with hare-brained schemes to misuse
the hidden service protocol?

Cheers,
Michael
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