Key facts
- Zcash's Ironwood upgrade has activated, sealing the Orchard shielded pool.
- The Orchard pool held approximately 3.66 million ZEC, valued at $1.7 billion.
- A bug in the Orchard proof circuit could have allowed the creation of counterfeit ZEC.
- A 'turnstile' mechanism prevents more ZEC from leaving the old pool than was verifiably deposited.
- The upgrade introduces quantum-resilient record-keeping and formally verified proof circuits.
- Zcash researchers published over 2,700 machine-checked theorems to rule out counterfeiting bugs.
Zcash has activated its Ironwood (NU6.3) upgrade, a significant development that seals the Orchard shielded pool, which held approximately 3.66 million ZEC valued at $1.7 billion. This upgrade addresses a critical bug discovered in Orchard's proof circuit that could have allowed an attacker to mint counterfeit ZEC without leaving an on-chain trace. The Ironwood upgrade introduces a 'turnstile' mechanism at the boundary of the previous pool. This accounting rule caps total withdrawals from Orchard to the amount that has been verifiably deposited, effectively trapping any counterfeit coins within the old pool. While the bug was patched within days of its discovery, the four-year window it was active meant that the chain could not definitively prove counterfeit coins were never created. Ironwood also brings enhanced security features, including quantum-resilient record-keeping and formally verified proof circuits for the new pool, aiming to prevent similar bugs in the future. Zcash researchers have also completed formal verification of Ironwood, publishing a machine-checked proof comprising over 2,700 theorems to ensure the network's new shielded pool does not contain undetectable counterfeiting bugs under its stated cryptographic assumptions.