Zcash retires $1.7B Orchard pool after Ironwood upgrade activates
In brief
- Zcash activated Ironwood at block 3,428,143, retiring Orchard shielded pool worth $1.7 billion
- Orchard contained undetected counterfeiting vulnerability live since 2022 launch, discovered May 2026
- New pool enforces quantum-resistant cryptography and formal verification from first block
- Turnstile mechanism caps withdrawals at verified deposits, trapping counterfeit coins
The bug that went undetected
On May 29, Shielded Labs researcher Taylor Hornby found that Orchard's proof circuit contained a bug that would let an attacker mint counterfeit ZEC. The flaw had been live since Orchard launched in May 2022, meaning the vulnerability sat in production for nearly four years before discovery.
Developers patched the bug within days. But the core question lingered: had anyone exploited it?
Evidence points away from exploitation, according to a CoinDesk Research report from July. Orchard's balance grew steadily through the four years the flaw was open, including through last year's price rally, with no signs of sudden drainage or suspicious activity. The steady growth suggested the bug remained unknown outside the Shielded Labs team.
The turnstile mechanism
Ironwood held zero ZEC at activation, and every coin must be moved across by its owner. Migration is voluntary and user-driven. As of press time, 1,500 ZEC have already moved into the new pool.
The new pool enforces a hard accounting rule at its boundary. The only route out of Orchard is a turnstile — an accounting rule at the pool's boundary that caps total withdrawals at the amount verifiably deposited. This mechanism traps any counterfeit coins that might have been minted inside the old pool, preventing them from ever reaching the public ledger or being spent.
Quantum resistance and formal verification
Ironwood launched with quantum-resistant cryptography protections specified under ZIP 2005 from the first block. The pool's proof circuit, the code that checks every private transaction is valid, is undergoing formal verification, a mathematical proof process designed to rule out the class of bug that broke Orchard.
On the market, ZEC traded near $463 ahead of the switch, down 8% on the day and 15% over the week. Yet it remains up roughly tenfold over the past year.
