A cryptography professor at John Hopkins University has posted an “archival fork” of Tornado Cash’s source code to GitHub.

The professor, Matthew Green, says he intends to preserve the source code of the privacy protocol for research purposes, rather than for deployment. His students, he said, have used such code to learn concepts related to cryptocurrency privacy and zero-knowledge technology. 

“The loss or decreased availability of this source code will be harmful to the scientific and technical communities,” said the researcher in a post to GitHub on Monday.

Privacy in crypto is of deep interest to Green: as a developer, he is personally involved with Zcash, a cryptocurrency that uses zero-knowledge proofs to protect the anonymity of transactions. He was also responsible for proposing Zerocoin—a Bitcoin privacy extension back in 2013, although it’s not compatible with Bitcoin’s current system. 

However, the fork also represents Green’s public stand against the OFAC’s decision to sanction Tornado Cash, its software repositories, and its smart contract addresses on Ethereum. As he explained, applying economic sanctions against open-source software is a historical first for the United States government, and has crucial implications for the state of free speech.

“The Tornado Cash example raises the prospect that the U.S. government may use sanctions to ban source code distribution and scientific speech,” he said.

Furthermore, given the steep penalties that accompany sanctions violations, Green contends that the Tornado Cash precedent could carry a "chilling effect" that dissuades private internet companies from spreading similar code. In this way, Green argued that speech bans can effectively be enacted without using explicit government orders. 

GitHub, for example, removed Tornado Cash’s source code repositories within hours of the OFAC’s sanctions announcement. Furthermore, many cryptocurrency exchanges—and even DeFi protocols—have restricted services to users that interact with Tornado’s smart contract addresses.


“It is hard to believe that Github's decision was unrelated to the government's action,” said Green.

Green’s repository is just one of many forks to circulate in the Tornado Cash community in recent weeks. He also keeps multiple offline copies of all related repositories for safety, but is confident that GitHub won’t remove his current fork if hosted for non-deployment purposes.

“GitHub may see things differently;” he acknowledged. “If so, that would be fascinating.”

In a letter on Tuesday, U.S. congressman Tom Emmer slammed the U.S. Treasury for its Tornado Cash ban.

“The sanctioning of neutral, open-source, decentralized technology presents a series of new questions, which impact not only our national security, but the right to privacy of every American citizen,” wrote Emmer.

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