Zcash founder Zooko Wilcox has shared more details about the network’s upcoming Ironwood hard fork, scheduled for July 28, and how it will deal with concerns surrounding a previously discovered flaw in the Orchard shielded pool.
The upgrade is not designed to identify or freeze any potentially counterfeit coins. Instead, it will seal off the old Orchard pool and limit the amount of ZEC that can leave it. This approach is intended to protect the network even if the flaw had been exploited in the past.
The challenge for Zcash is that Orchard transactions are private by design. Because transaction details are hidden, developers cannot prove with complete certainty that no counterfeit ZEC was ever created. While the team believes the bug was unlikely to have been exploited, there is no way to verify that with absolute confidence.
Ironwood, also known as NU6.3, will activate at block 3,428,143 on July 28. Once activated, the current Orchard pool will be retired and replaced with a new shielded pool built using corrected cryptography.
After the upgrade, users will no longer be able to send or receive funds within the old Orchard pool. Any funds leaving the old pool must pass through a special mechanism called the “turnstile.” This system ensures that no more ZEC can exit the pool than the amount that legitimately entered it, effectively trapping any potential excess supply inside the retired pool.
The issue traces back to May 29, when security researcher Taylor Hornby discovered a flaw in Orchard during a security audit. The vulnerability could have allowed an attacker to create counterfeit ZEC within the private pool without leaving clear evidence on the public blockchain.
Developers quickly responded by disabling Orchard activity and later restoring it through the NU6.2 upgrade, which fixed the underlying cryptographic issue. Although no evidence of counterfeit coin creation was found, Zcash’s privacy features mean it is impossible to completely rule out the possibility.
For most users, no immediate action is required before the July 28 upgrade. However, exchanges, wallets, and other service providers may temporarily pause deposits, withdrawals, and related services while updating their systems to support Ironwood.
Users who hold funds in the old Orchard pool may eventually need updated wallet software to move their funds into the new shielded pool. Some wallets could temporarily limit access until migration tools become available.
The Orchard incident has also prompted broader security improvements across the Zcash ecosystem. Additional reviews, independent audits, and formal verification efforts are underway to strengthen the network and reduce the risk of similar vulnerabilities in the future.
Ultimately, Ironwood is designed to address the remaining uncertainty around Zcash’s supply. By sealing the old Orchard pool and tightly controlling withdrawals, the network aims to ensure that any hypothetical counterfeit ZEC can never enter wider circulation, helping preserve trust in the cryptocurrency’s monetary system.
