Zcash says Ironwood proof rules out undetectable counterfeiting bugsZcash researchers published more than 2,700 machine-checked theorems designed to rule out undetectable counterfeiting bugs in Ironwood.

Zcash researchers have completed a formal verification of Ironwood, the network’s new shielded pool, and published a machine-checked proof aimed at ruling out undetectable counterfeiting bugs under its stated cryptographic assumptions. The proof, written in the Lean programming language, includes over 2,700 theorems and was developed by three teams of researchers and cryptographers over more than a month. It establishes a security property called balance integrity, which ensures that the shielded pool cannot spend more value than has been publicly deposited into it.

The proof covers critical components necessary for balance integrity, including Ironwood’s zero-knowledge proof system, circuit rules, and ledger-level accounting. However, it does not address Ironwood’s privacy guarantees. Ironwood was introduced as part of Zcash’s NU6.3 upgrade in response to a vulnerability found in the earlier Orchard shielded pool, which theoretically could have allowed undetectable counterfeiting of ZEC coins. The Zcash developers stated that they found no evidence of the flaw ever being exploited.

As part of Ironwood’s design, funds migrating from the Orchard pool must pass through a public accounting checkpoint called a turnstile. This feature is intended to prevent any hypothetical excess coins from entering the new shielded pool and could also provide additional evidence over time about whether the earlier Orchard pool was exploited. The publication of this proof is significant because it aims to restore confidence in Zcash’s supply integrity following the earlier vulnerability.