[tor-dev] Namecoin .onion to .bit linking

[Jeremy Rand]

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Hello Tor-Dev,

One of the criticisms of Namecoin which seems to be raised sometimes
is that the current domain namespace spec doesn't have a method for a
.bit domain owner to prove that they are in control of a .onion.
(This is also an issue for .bit domains that point to .i2p.)  I'm
interested in improving this situation, and am looking for feedback.

First off, I'm curious what the various use cases are for this.  The
main use case I'm aware of is if a user is aware of a .onion domain
already, and is trying to find a human-memorable way to access it.
(As far as I can tell, the reverse is not a use case, because if you
already trust the .bit domain by name but don't know what .onion
you're looking for, presumably Namecoin already does what you want.)
Is this correct?  Am I missing any other significant use cases?

Second, I'm looking for feedback on my rough approach.  The approach
I'm looking at right now is to have a Namecoin namespace for .onion
backlinks to .bit domains, which is separate from the Namecoin
namespace for .bit domains.  The backlink namespace would have a name
field whose prefix is the .onion domain.  We can't prevent a squatter
from registering an exact match of the .onion in Namecoin, but by
using a prefix and checking the signature on all matches, we can avoid
the impact of squatters.  (The cost of obtaining new names would be a
deterrent for someone trying to flood a .onion prefix with invalid
backlinks as a DoS.)  The value field would contain a signature of the
domain name being pointed to, signed by the .onion key.  The .onion
key could also sign revocations of an endorsement of a .bit domain;
these would also be in that namespace.  Is this generally a good
approach?  I'm aware that cross-protocol attacks need to be carefully
considered when signing things with a .onion key -- do you have
suggestions on how I can sign a short JSON string of the rough form
{"name": "d/domain", "rev": 0} (which corresponds to endorsing
domain.bit, and not being a revocation of that .bit domain) in a way
that won't open up attacks on the .onion key's normal protocol usage?

I'll write up a more formal spec after feedback is received, just to
make sure I'm not missing some important details.

Cheers,
- -Jeremy Rand
https://namecoin.org
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