The Ironwood upgrade replaces Orchard, which had a hidden counterfeiting vulnerability for four years. Now, all coins must exit through a gate that limits withdrawals to confirmed deposits.
By Shaurya Malwa|Edited by Nikhilesh De Jul 28, 2026, 2:35 p.m. 3 min read
Zcash has successfully implemented its Ironwood (NU6.3) upgrade, effectively sealing the Orchard shielded pool, which contained approximately 3.66 million ZEC, and initiating a transition to a new private pool that starts with no coins.
The Orchard pool was previously compromised by a bug in its proof circuit that could have allowed for the creation of counterfeit ZEC without leaving an on-chain trace. This prompted the transition to Ironwood, which introduces a turnstile mechanism that limits withdrawals to the amount that has been verified as deposited.
Ironwood, activated at block 3,428,143, marked the retirement of Orchard, which held about 3.66 million ZEC valued at around $1.7 billion based on current market prices.
Upon activation, Ironwood held no ZEC, as tracking tools indicate. Coin holders must individually transfer their assets, and the only way to exit Orchard is through a turnstile — a regulation that caps withdrawals at the amount that can be verified as deposited.
Shielded pools, like Orchard, are designed to maintain privacy regarding the amounts of coins and the identities of participants, with a zero-knowledge proof ensuring that the deposited amount is publicly validated.
In May, Taylor Hornby, a researcher at Shielded Labs, revealed that Orchard contained a flaw that could enable an attacker to create counterfeit ZEC without detection. This bug had been present since Orchard's launch in May 2022.
However, a report from CoinDesk Research in July indicated no signs of exploitation. If counterfeit ZEC had been created, it would likely have been moved and sold, which would have shown up as a reduction in the pool's balance. Instead, Orchard's balance consistently increased over the four years the bug was active, including during last year's market rally when selling would have been most advantageous.
The developers quickly addressed the flaw, but they could not account for the four years it remained unpatched. Since zero-knowledge proofs do not reveal anything beyond what they confirm, there is no record on the chain to indicate whether any transactions in Orchard actually occurred, nor can anyone prove that counterfeit coins were not generated.
The turnstile mechanism addresses these concerns. Transactions entering or exiting a shielded pool are publicly disclosed, even if the internal transactions remain private, ensuring that the network knows the total amount of ZEC that entered Orchard and will not permit more to exit than that amount. Any counterfeit coins would remain trapped within the pool.
As of the latest updates, 1,500 ZEC have already transitioned into the new pool, according to tracking data.
The Ironwood upgrade also introduces two new security features absent in Orchard. The record of each coin's movement on the blockchain is designed to remain recoverable in the event that quantum computers eventually compromise current cryptographic methods, a safeguard outlined under ZIP 2005 and effective from the first block.
Additionally, the proof circuit, which validates each private transaction, is undergoing formal verification, which aims to produce a mathematical assurance that the software operates correctly under all possible scenarios, thereby eliminating the class of bugs that affected Orchard.
At the time of the upgrade, ZEC was trading around $463, reflecting an 8% decrease for the day and a 15% decline over the week, though it remains approximately ten times higher than its value a year ago.
The key metric to monitor moving forward is the speed at which the 3.66 million ZEC is transferred. This migration is voluntary and driven by users, and until it occurs, the majority of Zcash's private supply will be locked in a pool that is no longer accessible for new deposits.