Zcash Ironwood upgrade at block 3.4M activates new shielded pool

Zcash activates Ironwood on July 28, introducing a new shielded pool and turnstile to improve supply verification after an Orchard bug.

Zcash activates its Ironwood network upgrade at block 3,428,143 on July 28, replacing the Orchard shielded pool with a separately tracked system that improves circulating-supply verification.

"The turnstile mechanism prevents more ZEC from leaving Orchard than entered, giving users a public check on circulating supply without exposing private balances," the Zcash Foundation said in its Zebra 6.0.0 release notes.

The upgrade follows the disclosure of a flaw in the older Orchard pool that could have allowed an attacker to create counterfeit ZEC without an obvious public record. Developers patched the bug through emergency upgrades in June and said they found "no evidence" of exploitation, though Zcash's privacy design prevents them from proving hidden inflation never occurred. Zcash founder Zooko Wilcox said the flaw was "unlikely to have been exploited," while also stating that users should not need to rely on that assessment.

Ironwood also introduces quantum-recoverable notes under ZIP 2005, binding additional data into note construction for potential recovery through a future post-quantum protocol. The change does not make current Zcash transactions quantum-secure — a separate recovery protocol must still be designed and activated later. Funds remaining in Sprout, Sapling or Orchard will not gain this recovery option.

Turnstile Limits Value Leaving Orchard

Ironwood reuses Orchard's Action structure and Halo2 proof system but adds a separate note commitment tree, nullifier set, chain value pool and chain-history data, according to the Zebra 6.0.0 release notes. These records let nodes track the new pool independently from Orchard after activation. After the fork, Orchard will stop accepting new outputs and internal transactions. Funds can move out, but the accounting rule prevents more ZEC from leaving Orchard than the amount that legitimately entered it, leaving any excess hidden value trapped inside the pool once it becomes exit-only.

Zebra Becomes Mandatory as zcashd Support Ends

The upgrade completes Zcash's move away from the older zcashd node software. The network set zcashd's end-of-support halt at block 3,417,100, before Ironwood activation, leaving Zebra as the required node implementation for the new rules. Zebra 6.0.0 includes a separate mempool security fix that rejects expensive-to-check, non-standard transactions before the costly verification step. The Zcash Foundation said the flaw affected availability only and did not allow invalid blocks, lost funds or consensus failure.

Existing Orchard addresses can receive Ironwood notes, reducing changes for users. Wallet developers must still add migration support. Users whose wallets do not update may face delays when moving Orchard funds, while exchanges may briefly pause deposits or withdrawals around the fork.

This article is for informational purposes only and does not constitute investment advice.