Zcash’s Tachyon project was announced on July 29. It completed formal verification of the Ironwood shielding pool and released a machine-verified proof containing more than 2,700 theorems written in the Lean programming language. The verification establishes a security property called “Balance Integrity,” effectively ruling out the possibility of an undetectable forgery vulnerability existing in Ironwood under its established cryptographic assumptions.
Tachyon Project Formal Verification Completed: Over 2,700 Lean Theorems
The formal verification work for the Tachyon project was carried out in collaboration by three researchers and a team of cryptographers, taking more than a month. The final released machine-verified proof includes more than 2,700 theorems, all written in the Lean programming language. The significance of this verification is that it is “machine-verified”—meaning a computer automatically checks the correctness of every logical step, rather than relying solely on manual review, thereby providing higher certainty.
Tachyon stated that the completed verification provides a mathematical guarantee that the Ironwood shielding pool contains no undetectable forgery vulnerabilities under its established cryptographic assumptions.
“Balance Integrity” Security Property: A Mathematical Guarantee That the Protected Funds Pool Won’t Overpay
“Balance Integrity” is the core security property established by this formal verification. Its mathematical definition is that the amount paid out by the protected Ironwood funds pool will not exceed the amount publicly deposited into it. To achieve this property, the verification work covers the following components:
· Ironwood’s zero-knowledge (ZK) proof system
· Circuit rules: the foundational computational rules that make up Ironwood’s logic
· Ledger-level accounting: a funds-tracking and bookkeeping mechanism across the entire network layer
It is noteworthy that this proof does not cover Ironwood’s independent privacy-preserving measures. The researchers said that privacy guarantees are a separate security property and need to be verified separately.
Background on the Orchard Vulnerability and the “Revolving Door” Public Accounting Mechanism
The direct reason for the Ironwood shielding pool was a vulnerability found in the Orchard security pool—one that could theoretically lead to ZEC forgery behavior that cannot be detected, thereby threatening Zcash’s supply integrity. Zcash introduced Ironwood in the NU6.3 version upgrade. Developers said there is no evidence that any vulnerability has been exploited in practice, and the new shielding pool is intended to restore public confidence in Zcash’s supply integrity.
Funds transferred from Orchard must pass through a public accounting checkpoint called the “Revolving Door,” intended to prevent any hypothetical excess tokens from entering Ironwood. As funds continue to flow out of Orchard, this process may also gradually provide more evidence to assess whether the old shielding pool was ever abused.
FAQ
How many theorems does the Ironwood formal verification in the Tachyon project include, and what tools were used to complete it?
According to the Tachyon project announcement, this formal verification includes more than 2,700 theorems, all written in the Lean programming language. It took more than a month to complete with three researchers and a team of cryptographers. The final result is a machine-verified mathematical proof in which the computer automatically checks every logical step.
What exactly does the “Balance Integrity” security property guarantee?
“Balance Integrity” guarantees that the amount paid out by the protected Ironwood funds pool will not exceed the amount publicly deposited into it. This verification covers all components needed to achieve this property, including Ironwood’s zero-knowledge proof system, circuit rules, and ledger-level accounting; however, it does not cover Ironwood’s independent privacy-preserving measures.
Why does Zcash need to introduce Ironwood, and has the Orchard vulnerability been exploited?
Ironwood was introduced by Zcash in the NU6.3 version upgrade to address a vulnerability found in the Orchard security pool—one that could theoretically lead to undetectable ZEC forgery behavior. Zcash’s development team said there is no evidence that this vulnerability has been exploited in practice, and the new shielding pool is intended to restore public confidence in Zcash’s supply integrity.
