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Hello everyone,
I have a proposal for Tor hidden services, which if it's a good idea
and workable I may be writing my Master's thesis on. My description
here is very early, and I would like to run it by you guys before I
continue further. I have already run it past Tor developers, but
have seen limited response, so I'm opening it up to a wider
audience. Basically, I propose integrating Namecoin into supporting
Tor relays, so as to provide a secure DNS service for .onion sites
within Tor itself. The result is that a human-readable address can
be translated into its .onion counterpart, analogous to a domain
name resolving into an IP address on the regular Internet, a square
of Zooko's Triangle conjecture.
Namecoin has a nearly identical codebase to Bitcoin, but instead of
currency its primary focus is holding information, with a focus in
DNS. Domains in Namecoin have the .bit extension, and registrations
are secured with hashes in a blockchain. Anyone with the Namecoin
blockchain can look up information in it, and indeed there are
already Namecoin-supporting DNS servers that use the Namecoin
blockchain to look up registrations in it. These basic premises are
at the heart of my idea. Now, 3g2upl4pq6kufc4m.onion is the address
for the DuckDuckGo hidden service, but it's hard to remember: even
worse than a traditional IP address. Under my idea, a user could
type in duckduckgo.tor, would see a secure translation to
3g2upl4pq6kufc4m.onion transparently and with masking, increasing
the usability and popularity of hidden services significantly.
My plan is in the context of Tor, to use the .tor domain, so as to
not conflict with existing Namecoin registrations. The .onion
address is a hash of the hidden service's public key, so if I own
the private keys to 3g2upl4pq6kufc4m.onion, I should be able to sign
something (perhaps the Namecoin public DSA key) to prove my
ownership and set duckduckgo.tor.bit to point to
3g2upl4pq6kufc4m.onion. I then upload this to the Namecoin network
as usual, (this costs 0.01 Namecoin) so that it becomes integrated
into the blockchain. So now duckduckgo.tor.bit points to
3g2upl4pq6kufc4m.onion, and everyone with the blockchain knows it.
Global DNS propagation may take less than 15 minutes. Namecoin
domain registrations expire after 36,000 blocks (about 200 days) so
a registration would have to be renewed occasionally for it to still
remain. This is free to do, but ensures that domains don't endure
indefinitely.
It's impractical for Tor users to download the Namecoin blockchain
in order to use this system, (even with Merkle trees) so instead
supporting Tor relays can hold a copy and the Tor client can send
out queries to them. At startup, Tor clients build several circuits
through the network in preparation for use. Now let's say the user
wants to look up duckduckgo.tor. To avoid spoofing attacks from a
malicious relay, Tor clients will query multiple relays and gain a
consensus. To do this, the Tor client generates three nonces, N1,
N2, and N3. It then picks three random relays, possible trusted
relays like guards, R1, R2, and R3. These relays have public RSA
keys K1, K2, and K3, respectively. For each of the three relays, the
Tor client takes the request for duckduckgo.tor, nonce Nj, and
encrypts the pair with the relay's public key Kj. Along with a
special new Tor flag specifying the use of this protocol, it then
sends the trio through the circuit to the middle relay. The middle
relay then queries the three relays. Each relay decrypts the request
using its private key, checks the blockchain for duckduckgo.tor.bit,
finds 3g2upl4pq6kufc4m.onion, and encrypts this answer with the
nonce, and sends it back, signing the result. The client receives
the answers, checks the signatures, decrypts the responses from the
three relays using the nonces, and compares the response. If all
three match, it then looks up 3g2upl4pq6kufc4m.onion in the
traditional way. If two or less match, it restarts with a different
set of three relays. If all three relays return that duckduckgo.tor
can't be found, it throws the standard DNS error message.
So I am simply building on top of the existing Tor hidden service
infrastructure, not modifying it. I can write up a proposal for
torspec.git once I have more details. I've already taken Tor
0.2.5.6-alpha code, installed Tor from source, and used Chutney to
set up a mini Tor network on localhost of 5 authorities, 10 relays,
and 1 client. That seems a good platform for development on this.
What do you guys think about my proposal? Is this a good idea, and
feasible? Anything I should watch out for as I go forward? What
security threats exist that I should specifically defend against?
Thank you for your time.
- --
Jesse V.
/CS, Network Security/
/Utah State University/
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