Zcash Ironwood hard fork arrives on July 28. Founder Zooko Wilcox explained how it will address a critical Orchard flaw.
The upgrade will not identify individual counterfeit coins. Instead, it will seal the old pool. It will also limit how much ZEC can leave.
Zcash Ironwood hard fork seals the vulnerable Orchard pool
Wilcox posted on X on July 19. He explained the planned upgrade’s approach. Orchard hides transaction details. Therefore, the network cannot prove no counterfeit ZEC was ever created.
Ironwood (NU6.3) activates at block 3,428,143. The upgrade will retire the current Orchard pool. It will introduce a new shielded pool. This pool uses the corrected circuit.
After activation, users cannot send or receive ZEC in the old pool. Funds can leave only through the turnstile. The turnstile prevents more ZEC from exiting than legitimately entered.
The Zcash team believes the flaw was “unlikely to have been exploited.” Nevertheless, users cannot independently prove no counterfeit ZEC was created. Ironwood traps any excess value inside the old pool. This prevents it from entering wider circulation.
Orchard bug left a supply question Zcash could not prove away
Security researcher Taylor Hornby discovered the flaw on May 29. He audited the shielded system. The bug could have allowed an attacker to create counterfeit ZEC. The attack would leave no obvious public record.
Developers first disabled Orchard activity. They then restored it through the NU6.2 hard fork. The fork included corrected cryptography. No evidence of unauthorized value creation emerged.
Nevertheless, Orchard’s privacy means past exploitation cannot be ruled out. Ironwood creates a fresh shielded pool. The turnstile controls value leaving the old pool.
Node operators can verify circulating ZEC. It will not exceed the network’s monetary rules.
Wallets and exchanges may temporarily pause services
Zcash users do not need immediate action. However, wallets and exchanges may temporarily suspend services. They need to complete software upgrades.
Orchard users will need wallet support. They must move funds into the new pool. Funds may remain temporarily unavailable. This applies to wallets without migration tools.
The July 28 activation follows Zcash’s move away from zcashd. Providers still completing that migration may need more time.
Zcash adds more security checks after the flaw
The Orchard incident led to wider security work. An AI-assisted review found no additional serious vulnerabilities. Anthropic’s Mythos system conducted the review.
Developers are also pursuing independent audits. They are working on formal verification. This aims to reduce the risk of another hidden flaw. It also gives users stronger supply verification.
Ironwood addresses the unresolved supply question. It does not fix the already-patched bug. By sealing Orchard and controlling withdrawals, the hard fork prevents any hypothetical counterfeit ZEC from circulating.
