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The carbon footprint of TOR (The Onion Router) network

The TOR (The Onion Router) network has been around for quite some years now, but do we know what its carbon footprint is? I have been searching around the internet but without luck, so now I take it into my own hands to create some relatively reasonable estimates of how much the TOR network is polluting. Everything in this article is based on information that either comes from TOR's own website or trusted sources.

What is TOR?

The TOR (The Onion Router) network was developed by the US Navy in the mid-1990s as a means of protecting government communications. It was later released as open-source software and became a popular tool for preserving online privacy and bypassing censorship. The TOR network works by routing internet traffic through a series of servers, or "nodes," each of which only knows the location of the preceding and following nodes in the circuit. This makes it difficult for anyone to determine the origin or destination of the traffic. In addition to providing privacy and security, the TOR network is also used by journalists, activists, and others to access information and communicate anonymously in countries with strict internet controls.

How many TOR relays exist?

At the beginning of 2023, there were approximately 6,500 relays in the TOR network, and about 1,700 of these are considered exit nodes. The number of relays can fluctuate due to various factors such as the availability of volunteers to run them and changes in the network configuration. TOR relies on volunteers to provide server resources, so the number of relays can change over time as more people participate or as existing relays go offline. The total number of relays, along with their geographic distribution, helps to determine the speed and reliability of the network. So the more people who set up a TOR relay, the faster it becomes.

There are 3 types of relays:

  • Entry relay (Guard)
  • Middle relay
  • Exit relay

The first relay is the guard, and it knows the IP address of the person connecting to it. The middle relay is a type of relay that distributes information about the next step in the chain. They don't know the real identity of the person connecting to the TOR network. The last step is the exit relay, which is the node that will connect to the destination (website). The exact setup of how the entry, middle, and exit relays work and are chained together is a science in itself.

According to TOR's website, non-exit relays should be able to handle 7,000 concurrent connections (Which can be overwhelming for most consumer routers), and exit relays should be able to handle +100,000 concurrent connections. It is also mentioned that a TOR relay should be unmetered which means they will use approximately 2 terabytes of data both up and downstream every month.

How many use TOR network?

According to Truelist, more than 2 million people use the TOR network every single day. The reasons vary; some use it to access valuable information on the internet, others to hide their identities because of their jobs, and others to pursue illegal activities. There are more than 65,000 dark web domains ending with .onion, but traffic to these domains only accounts for approximately 1.5% of the traffic. There is no doubt that the dark web is enormous, and things are going on in that place, that we won't even speak of.

People all over the world are using TOR, and every day the network is growing bigger. People are adding more relays to the network by using their own devices as a contribution. Even a single Raspberry Pi can contribute to the network. According to TOR's own statistics measured from 2014 till today, the US has the biggest amount of users.

  • USA: 19.10% (423,812 daily users)
  • Germany 10.62% (235,713 daily users)
  • Russia 10.41% (230,974 daily users)
  • France 4.64% (102,894 daily users)
  • United Kingdom 3.27% (72549 daily users)

The estimated carbon footprint

Now that you know a bit about the TOR project, it is time to create an estimate of how much the network pollutes. Doing this is not easy, so please don't take my estimates as being 100% correct. There are many factors that I am only assuming because I don't hold the exact information. But I believe that the estimates can be used to paint a picture of how massive it is.

We can start by measuring how much it pollutes to run a middle relay since it is the most common one to run. Earlier in the article, we learned that a middle relay (non-exit relay) should be able to run 7,000 concurrent connections which can be hard for most consumer routers. The relay will also need to run 24/7, which means it will never be turned off. In this example, we can use a Raspberry Pi and turn it into a middle relay. 

According to this website, a Raspberry Pi 4B with 8GB of RAM consume a maximum of 6 watts when all 4 cores are running at full speed. This means the Raspberry Pi alone will use approximately 0.144 kWh per day which is 4.32 kWh per month. A global estimate measured by the US Energy Information Administration states that 1 kWh of electricity in 2021 was equal to 0.855 pounds (0.387 kg) of CO2. This means the Raspberry Pi would have polluted with 3.69 pounds (1.67 kg) of CO2 in a month. When we then take into consideration that there are 6,500 current relays then we land at 23,986 pounds (10,879.87 kg) of CO2 in just a single month (IF all relays were run by Raspberry Pi's).

So, now we know that the relays alone would account for a minimum of 23,986 pounds (10,879.87 kg) of CO2 per month if all the devices were Raspberry Pis. In reality that is not true. The network is made up of a mix of virtual machines, computers, servers, etc, and it is impossible to know exactly how many there are of each. But if a computer is used to run a relay we could assume it would use 35 watts instead of 6 watts. By using Raspberry Pis we know the minimum pollution since most devices will use significantly more energy. 

The next logical step we can check is the consumer routers. Even though the TOR network is running outside the normal internet, it still requires regular internet access. This means the regular router in your home will be used as well. According to EnergySage, a regular consumer router will consume between 5 watts and 20 watts. So, for our tests, let's take an average between that and say that they use 10 watts. We know from earlier that even the smallest relays should be able and expect to handle 7,000 concurrent connections which is hard for most consumer routers. With this knowledge, we know that the routers will be consuming close to maximum watts because of the number of connections. So a router using 10 watts concurrently would use approximately 0.24 kWh per day, which will be 7.2 kWh per month. If we times that with 6,500 then we get 46,800 kWh per month which equals 40,014 pounds (18,150.04 kg) of CO2 per month.

So, now we can add together the numbers which will give us an estimate of 64,000 pounds (29,029.91 kg) of CO2 per month. This is based on if all relays are made of low-powered Raspberry Pis, and all consumer routers were using a maximum of 10 watts when being stressed. According to ICBE 1 ton of CO2 takes up approximately 556 m3 (cubic meters). So 29 tons would take up a space of approximately 16,124 m3 (cubic meters). That is equal to a stretch of 16 kilometers (9.94 miles) in each direction every single month! In just a single year that would be 768,000 pounds (348,358.9) of CO2 which would take up approximately 193,488 m3 (cubic meters). That is equal to 193 kilometers or 120 miles in each direction.

Now, you have a rough estimate of how much the TOR network is polluting in a single year. The estimate is of course not 100% correct since we assume all relays in the network is Raspberry Pi 4B's and all routers are consuming 10 watts max. We are also not considering that some countries have greener electricity and the actual amount of data that is being transferred. When streaming a movie through the TOR network you for example have to deal with the pollution caused by the network itself, and also the pollution caused by the internet (each gigabyte of data equals a certain amount of CO2). We are also not considering the power consumption of the daily user's devices such as phones, tablets, and laptops, and not either their routers. If we zoom in and look closer at the actual amount of data, the distance the data is traveling, the amount of relays each request goes through, cryptocurrency trading, and all the other factors, then we will be seeing a much higher and scary number.


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