Sean Bowe

Sean Bowe is a cofounder of Zcash and the project’s first engineer. He designed and implemented Zcash’s zk-SNARK cryptography for the network’s 2016 mainnet launch, handled that work for every upgrade in the decade since, and coauthored several of the academic papers behind it. He worked for many years as an engineer and cryptographer at the Zcash Company, Zcash’s developer, later renamed the Electric Coin Company (ECC).⁠[1][1][2]

On March 1, 2018, Zcash Company cryptographer Ariel Gabizon discovered, during the Financial Cryptography conference, a subtle flaw in the [BCTV14] paper describing the zk-SNARK construction originally used by Zcash that could allow counterfeiting of shielded coins. That night he contacted Bowe, also at the conference, to confirm it, and the two immediately informed CEO Zooko Wilcox. Bowe proposed covertly fixing the flaw through the upcoming Sapling network upgrade by switching to the Groth16 proving system and parameters from a new ceremony, and the team adopted his recommendation. Sapling activated on October 28, 2018, removing the vulnerability, which until then had been known to only four people; in November of that year, Bowe reconstructed and published the original ceremony transcript from DVDs kept by its participants.⁠[3][3][3][3][3][3]

In an ECC interview series that September, Bowe said he believes privacy is a human right and expressed optimism about regulation, saying regulators were beginning to understand that privacy is necessary for finance and for decentralized financial models.⁠[4][4]

On September 10, 2019, ECC announced that Bowe, its engineer and cryptographer, had discovered Halo, a technique for practical zero-knowledge recursive proof composition without a trusted setup; the paper was coauthored by Bowe, Daira Hopwood and Jack Grigg. By repeatedly applying “nested amortization” over cycles of elliptic curves, Halo lets a proof efficiently verify another instance of itself, removing the need for trusted setups, which are hard to coordinate and pose systemic risk. ECC released the paper and prototype implementation free under an open-source license, with no patent restrictions.⁠[5][5][5][5][5][5]

On April 2, 2025, Bowe proposed Tachyon on his blog, a set of protocol changes to make Zcash’s shielded transactions scalable. He argued that Zcash’s scaling bottleneck lies not in zk-SNARK verification but in communicating and coordinating global state; the core of the plan is “oblivious synchronization,” combined with proof-carrying data (PCD) to compress shielded transactions in blocks and a shift to out-of-band delivery of payment information. He said the plan could be built with cryptography Zcash already knows how to deploy and did not depend on speculative research. On April 17 he introduced Ragu, a Rust recursive proof toolkit he was building for it, and on May 15 he explained that Tachyon would remove in-band secret distribution and simplify the key structure.⁠[6][6][6][6][6][6][7][8]

On October 16, 2025, Bowe wrote about Zcash and quantum computers, arguing that Zcash’s shielded transactions already achieve post-quantum privacy in many common cases and that the main quantum threat is counterfeiting if elliptic curve cryptography is broken; he said Tachyon would remove in-band secret distribution to fully defend against quantum attacks on the privacy of on-chain transactions.⁠[9][9][9]

On March 17, 2026, Bowe was the guest at Zcash Engineering Office Hours #5, explaining Project Tachyon. The organizers described Tachyon as led by Bowe, the cryptographer behind Halo and Sapling, and aimed at letting wallets stay current without downloading the whole chain or revealing what they are looking for, while freeing validators from unbounded state growth.⁠[10][10][10]

After the Orchard counterfeiting vulnerability was disclosed, Bowe wrote on X on June 5 that shielded protocols trade privacy for reliance on cryptographic assumptions, that there is no shortcut for checking what happens inside a pool, and that the only answer is to rely on safe assumptions and make the code flawless by formally verifying shielded protocols and their implementations. On June 6, he and Dev OjhaDev OjhaDev Ojha is a cryptographic engineer, an early member of the Cosmos team, and a co-founder of the decentralized exchange Osmosis; since 2026 he has led Valar Group, which focuses on Zcash protocol research and development, and co-maintains the Zcash full-node software Zakura with Sean Bowe.Open the full entry of Valar GroupValar GroupValar Group is a cryptography research and engineering team focused on developing the Zcash protocol, led by Osmosis co-founder Dev Ojha and staffed largely by engineers from Osmosis and Celestia; in 2026 it took part in the Ironwood network upgrade, released the full-node software Zakura with Project Tachyon, and built Zcash’s private coinholder voting chain.Open the full entry proposed Ironwood in a joint statement by Project Tachyon and Valar Group: a new shielded pool reusing the Orchard protocol, with payments in the old pool halted so that any hypothetical counterfeit coins would have to pass through the turnstile, thereby auditing the Orchard pool’s supply.⁠[11][11][11][11][12][12][12][12]

On July 15, 2026, Bowe and Dev Ojha released Zakura 1.0.0, a new full node forked from the Zcash Foundation’s Zebra codebase; in testing it synced mainnet in about four hours and 20 minutes versus roughly 20 hours and 46 minutes for Zebra. The two said their long-term goal is throughput of about 50,000 transactions per second for private payments. Zakura is developed jointly by Project Tachyon and Valar Group, with Bowe as one of its maintainers.⁠[13][13][13][13][1][1]

On July 28, the day Ironwood activated as NU6.3, Bowe and Tal Derei published a machine-checked proof written in Lean, comprising more than 2,700 theorems, showing that Ironwood has no undetectable counterfeiting bugs; three research teams took more than a month to complete it. On August 14, he applied on behalf of Project Tachyon to the Coinholder Retroactive Grants Program for $738,942 for this work, and on September 29 he thanked coinholders for approving the grant.⁠[14][14][14][2][2][2]

On September 4, 2026, addressing the NU7 poll question of when to disable v4 transactions, Bowe argued for disabling them in NU7, which would indefinitely freeze Sprout, the original shielded pool usable only with that format, and for a recovery protocol built on a new extensible transaction format that lets holders retrieve funds through the turnstile. He noted that he had played a part in fixing the 2018 Sprout counterfeiting vulnerability and called the pool pure technical debt and a needless security risk.⁠[15][15][15][15][15][15]

On October 9, 2026, Bowe spoke as Tachyon’s representative at the Zcash Zummit session of Network State Conference 2026 in Singapore, where the conference introduced him as a Zcash cofounder.⁠[16][16]

Bowe describes himself as a cryptographic engineer and researcher focused on zk-SNARKs, recursive proofs, privacy-preserving protocols and efficient, safe cryptography implemented in Rust. Papers he has coauthored include Recursive Proof Composition without a Trusted Setup, a zk-SNARK paper on universal and updateable structured reference strings, scalable multi-party computation for zk-SNARK parameters in the random beacon model, and Zexe, on decentralized private computation. As of October 2026, he is lead cryptographer of Project Tachyon, a Zakura maintainer and a ZIP editor.⁠[17][17][17][17][17][18][1]

Personal website: https://seanbowe.com/ (opens in a new window)⁠[17]

Project Tachyon: Official website: https://tachyon.z.cash/ (opens in a new window).⁠[19]

Zakura: Official website: https://zakura.com/ (opens in a new window).⁠[19]

X: Public account: https://x.com/ebfull (opens in a new window)⁠[17][19]

GitHub: Public account: https://github.com/ebfull (opens in a new window)⁠[17]