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Zcash developers plan a fix to keep ZEC swaps private from future quantum computers
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- DeepHorus
Zcash developers behind Zakura have proposed giving every ZEC swap through NEAR Intents its own viewing key. The fix aims to stop a refund address on NEAR’s public chain from exposing a user’s wider payment history. It targets a future quantum-computer threat. The proposal would keep spending keys with users.
Zcash is designed for private payments. NEAR Intents lets users swap tokens across blockchains. When someone swaps private ZEC for USDC, the service posts a Zcash refund address on its public chain, even if no refund is needed. That address stays public after the deposit lands.
Today’s computers cannot reverse that address into a viewing key. A large quantum computer running Shor’s algorithm, published in 1994, could theoretically do so. Last week, Google said its Willow chip produced near-perfect versions of a component for such an attack. No such machine has been demonstrated, and no timeline is firm.
The risk is serious because Zcash wallets usually share one viewing key across many addresses. Cracking it from one published address could link every payment, amount, and memo. Spending keys stay separate, so funds remain safe. An attacker would see only payments tied to one swap.
Zakura says compatible wallets could adopt the open-source feature within weeks. That is before Zcash developers’ January target for quantum-resistant payments. The design uses private information retrieval so wallets can find refunds without revealing which addresses they check.
The fix also handles wallet restoration. A wallet with hundreds of swaps would hold hundreds of keys, requiring a full chain scan. A privately queried database solves that. Zakura’s database answers queries without learning the addresses. No quantum computer has yet recovered these keys, but developers are acting early.
