Zakura, a team building Zcash node and wallet software, published a design that would give every shielded address posted during a NEAR Intents swap its own viewing key, limiting what a future quantum computer could learn from any single one. Zakura’s engineering page lists the work as in review, and it has not shipped.
Adam Tucker, who wrote the post, said that until Zcash’s planned Tachyon upgrade arrives, “a single published shielded address lets a quantum attacker link every payment that address’s key has ever received.”
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Why Swaps Expose Addresses
Each Zcash shielded account relies on one incoming viewing key behind all of its addresses. Classical computers cannot work that key out from an address, but a sufficiently powerful machine running Shor’s algorithm could, exposing the value and memo of every payment the account has received, according to the post. No such machine exists yet.
In ordinary use, a Zcash holder gives an address privately to whoever is paying them. NEAR Intents, a cross-chain swap service, works differently. When a user swaps ZEC for another asset, the wallet supplies a shielded refund address, and NEAR publishes the address on-chain once the deposit is logged, and it stays there whether or not the user gets money back. Swaps into ZEC publish the receiving address too. The addresses look unrelated, but one key sits behind all of them.
How the Proposed Fix Works
Zakura’s approach changes only the randomness that goes into the viewing key, deriving a fresh key for each swap from a hashed index. The spending key stays the same, so funds remain in a single account. Tucker wrote that opening a new account per swap was ruled out because Keystone hardware wallets sign only from the first account and Ledger devices spend from one account per transaction, “which wasn’t an acceptable UX to us.”
More keys would normally mean a slower restore from seed, with one full chain scan per key. Under the design, the wallet leaves itself an encrypted memo noting each swap’s index, checks published filters, then uses private information retrieval to look up matching NEAR bridge payouts without the server learning which addresses it asked about. For swaps into ZEC, the wallet checks addresses in order and stops after 30 unused ones in a row.
Zakura expects software wallets using its libraries, such as Vizor, to be able to add it “in the coming weeks.” “Hardware wallets will follow once their firmware supports it,” the post said.
Related Listen: How NEAR Intents Identified a Suspect and Got Its Stolen Funds Back
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