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Chapter 14.2: Changing Your Bitcoin Hidden Services

ℹ️ NOTE: This section has been recently added to the course and is an early draft that may still be awaiting review. Caveat reader.

You've got a working Tor service, but over time you may wish to reset or otherwise adjust it.

Secure Your Hidden Services

Tor allows you to limit which clients talk to your hidden services. If you did not already authorize your client during your server setup, at the earliest opportunity you should do the following:

  1. Request your Tor V3 Authentication Public Key from your client. (In GordianWallet, it's available under the settings menu.)
  2. Go to the appropriate subdirectory for your Bitcoin hidden service, which if you used Bitcoin Standup is /var/lib/tor/standup/.
  3. Go to the authorized_clients subdirectory.
  4. Add a file called [anything].auth. The [anything] can really be anything.
  5. Place the public key (and nothing else) in the file.

Once you've added an .auth file to the authorized_client subdirectory, then only authorized clients will be able to communicate with that hidden service. You can add ~330 different public keys to enable different clients.

Reset Your bitcoind Onion Address

If you ever want to reset your onion address for bitcoind, just remove the onion_private_key in your data directory, such as ~/.bitcoin/testnet:

$ cd ~/.bitcoin/testnet
$ rm onion_private_key

When you restart, a new onion address will be generated:

2020-07-22T23:52:27Z tor: Got service ID pyrtqyiqbwb3rhe7, advertising service pyrtqyiqbwb3rhe7.onion:18333
2020-07-22T23:52:27Z tor: Cached service private key to /home/standup/.bitcoin/testnet3/onion_private_key

Reset Your RPC Onion Address

If you want to reset your onion address for RPC access, you similarly delete the appropriate HiddenServiceDirectory and restart Tor:

$ sudo rm -rf /var/lib/tor/standup/
$ sudo /etc/init.d/tor restart

⚠️ WARNING: Reseting your RPC onion address will disconnect any mobile wallets or other services that you've connected using the Quicklink API. Do this with extreme caution.

Force bitcoind to Use Tor

Finally, you can force bitcoind to use onion by adding the following to your bitcoin.conf:

proxy=127.0.0.1:9050
listen=1
bind=127.0.0.1
onlynet=onion

You will then need to add onion-based seed nodes or other nodes to your setup, once more by editing the bitcoin.conf:

seednode=address.onion
seednode=address.onion
seednode=address.onion
seednode=address.onion
addnode=address.onion
addnode=address.onion
addnode=address.onion
addnode=address.onion

Afterward, restart tor and bitcoind.

You should now be communicating exlusively on Tor. But, unless you are in a hostile state, this level of anonymity is probably not required. It also is not particularly recommended: you might greatly decrease your number of potential peers, inviting problems of censorship or even correlation. You may also see lag. And, this setup may give you a false sense of anonymity that really doesn't exist on the Bitcoin network.

⚠️ WARNING: This setup is untested! Use at your own risk!

Summary: Changing Your Bitcoin Hidden Services

You probably won't need to fool with your Onion services once you've verified them, but in case you do, here's how to reset a Tor address that has become compromised or to move over to exclusive-Tor use for your bitcoind.

What's Next?

Continue "Understanding Tor" with 14.3: Adding SSH Hidden Services.