Subscribe to our Telegram channel!
A Zcash full-node software developer named Zakura has proposed a technical solution designed to protect users' private transactions from potential attacks by quantum computers. This is detailed in an engineering paper by developer Adam Tucker, published on Sunday.
The key feature of the proposal is that it does not require a network upgrade. Zakura called the approach «post-quantum unlinkable swaps for Zcash» and explained the mechanism of the threat: every protected account in Zcash has a single view key associated with all of its addresses. A classical computer cannot derive this key from an address, but a sufficiently powerful quantum computer using Shor’s algorithm is theoretically capable of doing so—and would then gain access to all of the account’s transactions and be able to link them together.
The biggest vulnerability, according to Tucker, is related to swaps via NEAR Intents—a cross-chain exchange service. Each swap involving ZEC records one of the user’s protected addresses on the public NEAR blockchain as the return address. The addresses look different, but they all belong to the same account—so by compromising one, an attacker gains access to all of them. According to Josh Swihart, CEO of the Zcash Open Development Lab, between $ 600 million and $ 700 million had passed through this route by May.
To solve the problem, Zakura proposes generating a separate view key for each address that needs to be published, without touching the account’s spend key. If a quantum computer compromises a single published swap address, it will only learn about payments made to that specific address—and will be unable to link it to other transactions.
To prevent additional keys from slowing down wallet recovery from a seed phrase, a technique called private information retrieval is used: the wallet can query the server about NEAR payments without revealing which specific addresses it is interested in. This same technique was used in Zakura’s previous proposal for quantum-secure transparent addresses, published in early October.
The issue of quantum security is becoming increasingly relevant for the cryptocurrency industry. Ethereum Foundation researcher Justin Drake and Ethereum co-founder Vitalik Buterin have already warned that even artificial intelligence could pose a threat to cryptography—before quantum computers do. In May, Schwahrt noted that Zcash plans to achieve full post-quantum status within 12−18 months.
Wallets based on the open-source Zakura libraries, including Vizor, will be able to integrate one-time keys for software wallets in the coming weeks. Hardware wallets will receive support following a corresponding firmware update. On Monday morning, ZEC was trading at $ 1,165, up 3.6% from the previous day.