These repositories contain an archival fork of the Tornado Cash and Tornado Cash Nova source code base. They are maintained on Github by Matthew D. Green of Johns Hopkins for teaching and research purposes.

See also: EFF blog post.

Tornado Cash and Tornado Nova are open-source coin mixing tools that were developed by an independent team of software developers and deployed onto Ethereum and several other blockchains. On August 8, 2022 the Office of Foreign Assets Control (OFAC), a division of the US Treasury, declared "Tornado Cash" and "Tornado Cash Nova" to be Specially Designated Nationals (SDNs): the result was to effectively sanction the Tornado Cash organization, its software development repositories, and the main smart contract deployment on Ethereum.

This move to sanction Tornado Cash represents the first instance in which the US government has applied economic sanctions to an open source software project. As a result of this announcement, several cryptocurrency exchanges have banned users who interact with the Tornado Cash smart contract address on Ethereum. Within hours of the OFAC announcement, Github shut down the user accounts of all known Tornado Cash developers and removed the source code repositories owned by Tornado's Github organization.

While Github succeeded in removing the original copies of all Tornado source code repositories, they did not remove all "forks" of the code made by GitHub users. Several of these forks were recently collected and (further) forked by contributors to the tornadocash-community organization. Those folks did the hard work. The current repository is simply another fork of the repositories they collected. (Note: some additional repositories have since been added, see below.)

In my work as a researcher and instructor at Johns Hopkins, I've made extensive use of the Tornado Cash and Tornado Nova source code to teach concepts related to cryptocurrency privacy and zero-knowledge technology. My students have built amazing projects from the code. The loss or decreased availability of this source code will be harmful to the scientific and technical communities.

Moreover, I am uncomfortable with the implications of the Github decision. Github is a private company, and of course it can suspend users for any perceived violation of its Terms of Service. At the same time, it is hard to believe that Github's decision was unrelated to the government's action. In my opinion it is much more likely that Github censored the Tornado Cash code repositories as part of a risk-mitigation procedure they engaged in as a direct result of the OFAC order. More critically: I believe that this removal of protected speech was a predictable consequence of OFAC's action, one that Treasury could easily have forseen and taken steps to avoid.

Given that much of the Internet publishing infrastructure is operated by private firms, the Tornado Cash example raises the prospect that the US government may use sanctions to ban source code distribution and scientific speech. Because sanctions rules are broad and carry extreme penalities, these speech bans do not need to be accomplished through explicit orders: they can be obtained simply by exposing US companies and citizens to the perception of sanctions risk. The result is a "chilling effect" on speech, one that allows the US government to determine which citizens and organizations do or do not enjoy the right to publish their source code and scientific artifacts.

The creation of this archival repository organization does not solve this issue. Nor will it repair the damage that has already been done by the OFAC order. The purpose of this repository is to make it clear to the US Treasury Department and Github that this code has value, and its removal has consequences that affect scientific researchers and students in the United States. Moreover, it exists to test the proposition that code removal should ever been an appropriate future response to a sanctions order, no matter how justified the order itself may be. I have discussed my concerns with the Electronic Frontier Foundation and they have agreed to represent me as a client. See their blog post here.

GitHub, as one of the most widely-used software distribution websites in the world, is an ideal place to host this repository. Deploying software on GitHub is more reliable than self-hosting on servers at the University: because of this I routinely use GitHub to host course material for my classes. At this moment I have no reason to believe that GitHub is opposed to the hosting of Tornado Cash's source code for non-deployment purposes.

GitHub may see things differently: if so, that would be fascinating. It goes without saying that I have made offline copies of all these repositories and will immediately re-publish them in a different location (such as a University server) if this site becomes inaccessible.

Git is a decentralized version control system. Hence other copies of the Tornado Cash code certainly exist on other machines and at other locations (in fact, go ahead and make a clone right now!) You should be able to verify that these are authentic by comparing hashes to a main trusted repository, like the one that used to be hosted here on Github. (Since that no longer exists, you can use the forks in this repository. Alternatively here's a Wayback Machine copy that still sort of works.)

Hence Github's removal of the Tornado Cash code repositories and developer accounts is not a total ban on the source code. It does have two critical effects: first, it halts the ongoing development of this source code even as a pure software development and research project. Second, it makes discovery of the code much more difficult. (It is more analogous to removing a book from major commercial bookstores, while still allowing users to exchange PDF files on USB sticks.) At present a non-expert user searching Google to find the Tornado Cash source will have a difficult time. Try it yourself!

If you want a copy of the code on a more durable decentralized medium, there are copies of (limited) repositories on IPFS. I certainly don't warranty these (or any of this code), and you should carefully check hashes against the repositories on Github and in the Wayback Machine just in case:

• Tornado Nova: ipfs://bafybeiho72nozeq2mi6egptem77omhujt5ovpx4jjskg5sz2ti57zlunmm
• Tornado Cash Classic: ipfs://bafybeicu2anhh7cxbeeakzqjfy3pisok2nakyiemm3jxd66ng35ib6y5ri

You can also find recent clones of the Tornado Cash repositories on Software Heritage.

These repositories are intended as an archival project only. They are yours to clone and fork. They will not be actively developed, which means that over time they will gradually become obsolete. If open source Tornado Cash development resumes (even under a different team of developers), I may periodically clone copies of their repositories here. In the future this organization may also evolve to host archival forks of other non-TC privacy projects, should I determine that they are also at risk of sanctions-based code removal.

After adding the initial repositories, several additional repositories were provided by anonymous contributors. These will be added one at a time after I have a chance to manually verify the hashes against cached copies of the original GitHub website. So far the public repositories include:

• tornado-onion
• tornado-trees-proposal

A new repository called GOOGLE_CACHE contains details on the hash verification, as well as links/copies of the cached web pages.