Zcash activates Ironwood upgrade after Orchard security flaw

Zcash has activated its Ironwood network upgrade, introducing a new shielded pool designed to strengthen the security of private transactions and make the integrity of the circulating ZEC supply independently verifiable.

The Ironwood NU6.3 upgrade went live Tuesday at block height 3,428,143. The upgrade also introduced a new transaction format supporting the Ironwood shielded pool.

Ironwood was developed following the discovery of a critical soundness vulnerability affecting Orchard, Zcash’s previous shielded pool.

Security researcher Taylor Hornby discovered the vulnerability on May 29 and privately disclosed it to Zcash developers. The issue affected the zero knowledge proof system used to validate Orchard transactions.

There is no evidence that the vulnerability was exploited, that user funds were affected, or that Zcash’s total supply increased.

However, the private nature of Orchard transactions means observers cannot examine the amounts inside the pool to definitively determine whether counterfeit ZEC was created.

Ironwood addresses the issue by restricting the original Orchard pool. New funds can no longer enter Orchard, while funds leaving the pool must pass through Zcash’s turnstile before entering Ironwood.

The turnstile places a protocol level limit on how much ZEC can leave Orchard, preventing the pool from paying out more value than it verifiably received. This creates an independently auditable boundary between Orchard and the new pool.

Ironwood uses a corrected version of the Orchard protocol alongside a separate note commitment tree, nullifier set, value pool, and transaction history data.

Zcash Open Development Lab said the new pool underwent formal verification and independent security review before its deployment.

The upgrade does not require users to create a new wallet or address. Ironwood uses the same receiver structure as Orchard, allowing compatible wallets to direct transactions sent to existing addresses into the new pool.

Users holding funds inside Orchard will need to migrate them to Ironwood through a supported wallet.

Zodl added Ironwood support through version 3.8.0 of its wallet. Users can manually migrate their Orchard funds through the application, while an automated migration system designed to provide stronger privacy protections is expected later.

Users without Orchard funds do not need to complete a migration, although Zodl advised all users to update their application to maintain compatibility with the upgraded network.

Node operators also need software capable of supporting NU6.3. Older versions that have not been upgraded will no longer follow the main Zcash chain after the Ironwood activation height.

The upgrade follows an emergency network response in June that temporarily restricted Orchard transactions while developers deployed an initial correction through NU6.2.

Ironwood provides a longer term replacement for the affected pool while preserving Zcash’s private transaction model and adding stronger guarantees around enforcement of the network’s monetary supply.

ZEC briefly advanced 5% on the announcement before reversing the move by midday.

Disclosure: This article was edited by Estefano Gomez. For more information on how we create and review content, see our Editorial Policy.