12 KiB
14.1: Verifying Your Tor Setup
ℹ️ NOTE: This is a draft in progress, so that I can get some feedback from early reviewers. It is not yet ready for learning.
If you did a standard installation with Bitcoin Standup then you should have Tor set up as part of your Bitcoin node. This section talks about what it is and what to do with it.
📖 What is Tor? Tor is a low-latency anonymity and overlay network based on onion routing and path-building design for enabling anonymous communication. It's free and open-source software with the name derived from the acronym for the original software project name: "The Onion Router".
📖 Why Use Tor for Bitcoin? The Bitcoin network is a peer-to-peer network that listens for transactions and propagates them using an IP public address. When connecting to the network not using Tor, you would share your IP address, which could expose your location, your uptime, and others details to third parties — which is an undesirable privacy practice. To protect yourself online you should use tools like Tor to hide your connection details. Tor allows improve your privacy online as your data is cryptographically encoded and goes through different nodes, each one decoding a single layer (hence the onion metaphor).
Understand Tor
So how does Tor work?
When a user wants to connect to an Internet server, Tor tries to build a path formed by at least three Tor nodes relays, called Guard, Middle, and Exit. While building this path, symmetric encryption keys are negotiated; when a message moves along the path, each relay then strips off its layer of encryption. In this way, the message arrives at the final destination in its original form, and each party only knows the previous and the next hop and cannot determinate origin or destination.
Here's what a connection looks like without Tor:
20:58:03.804787 IP bitcoin.36300 > lb-140-82-114-25-iad.github.com.443: Flags [P.], seq 1:30, ack 25, win 501, options [nop,nop,TS val 3087919981 ecr 802303366], length 29
Contrariwise, with Tor much less information about the actual machines is transmitted:
21:06:52.744602 IP bitcoin.58776 > 195-xxx-xxx-x.rev.pxxxxxm.eu.9999: Flags [P.], seq 264139:265189, ack 3519373, win 3410, options [nop,nop,TS val 209009853 ecr 3018177498], length 1050
21:06:52.776968 IP 195-xxx-xxx-x.rev.pxxxxxm.eu.9999 > bitcoin.58776: Flags [.], ack 265189, win 501, options [nop,nop,TS val 3018177533 ecr 209009853], length 0
Bottom line: Tor encrypts your data in such a way that it hides your origin, your destination, and what services you're using, whereas a standard encryption protocol like TLS only protects what your data contains.
Understand the Tor Network Architecture
The basic architecture of the Tor network is made up of the following components:
- Tor Client (OP or Onion Proxy). A Tor client installs local software that acts as an onion proxy. It packages application data into cells that are all the same size (512 bytes), which it then sends to the Tor network. A cell is the basic unit of Tor transmission.
- Onion Node (OR or Onion Router). An onion node transmits cells coming from the Tor client and from online servers. There are three types of onion nodes: input (Guard), intermediate nodes (Middle), and output nodes (Exit).
- Directory Server. A Directory server stores information about onion routers and onion servers (hidden services), such as their public keys.
- Onion Server (hidden server). An onion server supports TCP applications such as web pages or IRC as services.
Understand the Limitations of Tor
Tor isn't a perfect tool. Because information from the Tor network is decrypted at the exit nodes before being sent to its final destinations, theoretically an observer could collect sufficient metadata to compromise anonymity and potentially identify users.
There are also studies that suggest that possible exploits of Bitcoin's anti-DoS protection could allow an attacker to force other users who use Tor to connect exclusively through his Tor Exit nodes or to his Bitcoin peers, isolating the client from the rest of the Bitcoin network and exposing them to censorship, correlation, and other attacks.
Similarly, Bitcoin Tor users could be fingerprint-attacked by setting an address cookie on their nodes. This would also allow correlation and thus deanonymization.
With that said, Tor is generally considered far safer than the alternative, which is non-anonymous browsing.
Verify Your Tor Setup
So how do you verify that you've enabled Tor? If you installed with Bitcoin Standup, the following will verify that Tor is running on your system
$ sudo -u debian-tor tor --verify-config
If Tor is installed correctly you should see an output like this:
Jun 26 21:52:09.230 [notice] Tor 0.4.3.5 running on Linux with Libevent 2.0.21-stable, OpenSSL 1.0.2n, Zlib 1.2.11, Liblzma 5.2.2, and Libzstd N/A.
Jun 26 21:52:09.230 [notice] Tor can't help you if you use it wrong! Learn how to be safe at https://www.torproject.org/download/download#warning
Jun 26 21:52:09.230 [notice] Read configuration file "/etc/tor/torrc".
Configuration was valid
⚠️ WARNING: This just means that Tor is running, not that its being used for all connections.
Verify Your Tor Setup for Bitcoin
You can verify that a Tor hidden service has been created for Bitcoin with the getnetworkinfo RPC call:
$ bitcoin-cli getnetworkinfo
...
"localaddresses": [
{
"address": "173.255.245.83",
"port": 18333,
"score": 1
},
{
"address": "2600:3c01::f03c:92ff:fe86:f26",
"port": 18333,
"score": 1
},
{
"address": "zbyqk2tmq4c4vzeo.onion",
"port": 18333,
"score": 4
}
],
...
This shows three addresses to access your Bitcoin server, an IPv4 address (173.255.245.83), an IPv6 address (2600:3c01::f03c:92ff:fe86:f26), and a Tor address (zbyqk2tmq4c4vzeo.onion).
TESTNET vs MAINNET: Mainnet is run on port 8333, testnet on port 18333.
⚠️ WARNING: Obviously: never reveal your Tor address!
You can see similar information with getnetworkinfo.
bitcoin-cli getnetworkinfo
{
"version": 200000,
"subversion": "/Satoshi:0.20.0/",
"protocolversion": 70015,
"localservices": "0000000000000408",
"localservicesnames": [
"WITNESS",
"NETWORK_LIMITED"
],
"localrelay": true,
"timeoffset": 0,
"networkactive": true,
"connections": 10,
"networks": [
{
"name": "ipv4",
"limited": false,
"reachable": true,
"proxy": "",
"proxy_randomize_credentials": false
},
{
"name": "ipv6",
"limited": false,
"reachable": true,
"proxy": "",
"proxy_randomize_credentials": false
},
{
"name": "onion",
"limited": false,
"reachable": true,
"proxy": "127.0.0.1:9050",
"proxy_randomize_credentials": true
}
],
"relayfee": 0.00001000,
"incrementalfee": 0.00001000,
"localaddresses": [
{
"address": "173.255.245.83",
"port": 18333,
"score": 1
},
{
"address": "2600:3c01::f03c:92ff:fe86:f26",
"port": 18333,
"score": 1
},
{
"address": "zbyqk2tmq4c4vzeo.onion",
"port": 18333,
"score": 4
}
],
"warnings": "Warning: unknown new rules activated (versionbit 28)"
}
📖 What is a Tor Hidden Service? A hidden service (aka "an onion service") is a service that is accessible via Tor. Connection made to that service using the Onion Network will be protected. In this case, there is a hidden service for
bitcoindon Testnet, but there are also visible services using IPv4 and IPv6.
⚠️ WARNING: Running Tor and having a Tor hidden service doesn't force either you or your peers to use Tor.
Verify Your Tor Setup for Peers
Using the RPC command getpeerinfo, you can see what nodes are connected to your node and check whether they are connected with Tor.
$ bitcoin-cli getpeerinfo
Some might be connected via Tor:
...
{
"id": 9,
"addr": "nkv.......xxx.onion:8333",
"addrbind": "127.0.0.1:51716",
"services": "000000000000040d",
"servicesnames": [
"NETWORK",
"BLOOM",
"WITNESS",
"NETWORK_LIMITED"
],
"relaytxes": true,
"lastsend": 1593981053,
"lastrecv": 1593981057,
"bytessent": 1748,
"bytesrecv": 41376,
"conntime": 1593980917,
"timeoffset": -38,
"pingwait": 81.649295,
"version": 70015,
"subver": "/Satoshi:0.20.0/",
"inbound": false,
"addnode": false,
"startingheight": 637875,
"banscore": 0,
"synced_headers": -1,
"synced_blocks": -1,
"inflight": [
],
"whitelisted": false,
"permissions": [
],
"minfeefilter": 0.00000000,
"bytessent_per_msg": {
"addr": 55,
"feefilter": 32,
"getaddr": 24,
"getheaders": 1053,
"inv": 280,
"ping": 32,
"pong": 32,
"sendcmpct": 66,
"sendheaders": 24,
"verack": 24,
"version": 126
},
"bytesrecv_per_msg": {
"addr": 30082,
"feefilter": 32,
"getdata": 280,
"getheaders": 1053,
"headers": 106,
"inv": 9519,
"ping": 32,
"pong": 32,
"sendcmpct": 66,
"sendheaders": 24,
"verack": 24,
"version": 126
}
}
...
Some might not, such as this IPv6 connection:
...
{
"id": 17,
"addr": "[2001:638:a000:4140::ffff:191]:18333",
"addrlocal": "[2600:3c01::f03c:92ff:fe86:f26]:36344",
"addrbind": "[2600:3c01::f03c:92ff:fe86:f26]:36344",
"services": "0000000000000409",
"servicesnames": [
"NETWORK",
"WITNESS",
"NETWORK_LIMITED"
],
"relaytxes": true,
"lastsend": 1595447081,
"lastrecv": 1595447067,
"bytessent": 12250453,
"bytesrecv": 2298711417,
"conntime": 1594836414,
"timeoffset": -1,
"pingtime": 0.165518,
"minping": 0.156638,
"version": 70015,
"subver": "/Satoshi:0.20.0/",
"inbound": false,
"addnode": false,
"startingheight": 1780784,
"banscore": 0,
"synced_headers": 1781391,
"synced_blocks": 1781391,
"inflight": [
],
"whitelisted": false,
"permissions": [
],
"minfeefilter": 0.00001000,
"bytessent_per_msg": {
"addr": 4760,
"feefilter": 32,
"getaddr": 24,
"getdata": 8151183,
"getheaders": 1085,
"headers": 62858,
"inv": 3559475,
"ping": 162816,
"pong": 162816,
"sendcmpct": 132,
"sendheaders": 24,
"tx": 145098,
"verack": 24,
"version": 126
},
"bytesrecv_per_msg": {
"addr": 33877,
"block": 2291124374,
"feefilter": 32,
"getdata": 9430,
"getheaders": 1085,
"headers": 60950,
"inv": 2019175,
"ping": 162816,
"pong": 162816,
"sendcmpct": 66,
"sendheaders": 24,
"tx": 5136622,
"verack": 24,
"version": 126
}
}
...
⚠️ WARNING: Remember that the basic setup does not force usage of Tor. You may well see all IPv4 and IPv6 peers.
So what's the use of Tor if it doesn't force the usage of Tor for connections? The best use of the basic Tor setup is to allow a software wallet such as Bitcoin Standup Remote to connect to your node anonymously via the Tor hidden service, allowing you to remotely transact without anyone knowing you're doing so.
However, there are also fully anonymous setups that can be created for Bitcoin (though they are not recommended).
Summary: Verifying Your Tor Setup
Tor is a software package installed at part of Bitcoin Standup that allows you to exchange communications anonymously. It's the foundation of privacy and security for your Bitcoin setup, and you can verify it's available and linked to Bitcoin with a few simple commands.
:fire What is the power of Tor? Many attacks on Bitcoin users depend on knowing who the victim is and that they're transacting Bitcoins. Tor can protect you from that by hiding both where you are and what you're doing. It's particularly important if you want to connect to your own node remotely via a software wallet, and can be crucial if you do so in some country where you might not feel that your Bitcoin usage is appreciated or protected.
What's Next?
Continue "Understanding Tor" with §14.2: Changing Your Bitcoin Hidden Services.