Zakura Developer Proposes Solution to Protect Against Quantum Attacks

Zcash full node software developer Zakura proposed "disposable" viewing keys to prevent future quantum computers from linking a user's shielded payments. The solution does not require a network upgrade – developer Zakura Adam Tucker reported this in an engineering post on October 18, 2026, and Zakura announced it as "post-quantum unlinkable exchanges for Zcash."

Zcash shielded transactions hide the sender, recipient, and amount. Each shielded account has one incoming viewing key for all addresses: the wallet searches for and decrypts payments to any of them. A classical computer cannot recover the key from the address, but a sufficiently powerful quantum computer with Shor's algorithm could, and then it would see the amounts and memos of all the account's payments and link them. "Until Tachyon is released, there remains a gaping hole: one published shielded address allows a quantum attacker to link every payment that the address's key has ever received," Tucker wrote. Tachyon is a proposed Zcash scalability upgrade that, according to developers, will also provide full post-quantum privacy.

The main risk is exchanges through NEAR Intents. Each exchange from ZEC records one of the user's shielded addresses in the public NEAR chain as a return address, even if there will be no return. The addresses look different but belong to one account, so hacking one reveals all. By May, $600–700 million had passed through this route, reported Zcash Open Development Lab CEO Josh Swihart.

Zakura proposes generating a separate incoming viewing key for each published address without touching the account's spending key: hacking one address will only show payments to it. "If a quantum computer ever hacks a published exchange address, it will not be able to link it to other transactions," Tucker wrote. To prevent additional keys from slowing down recovery from a seed phrase, the wallet searches for NEAR payments through private information retrieval – a server query without revealing which addresses are being checked.

Earlier this month, Zakura introduced a plan for post-quantum transparent addresses, also with PIR; post-quantum signature opcodes are expected in Zcash in January. Swihart said in May that Zcash aims for full post-quantum status in 12–18 months. Concerns about wallet cryptography are growing: Ethereum Foundation researcher Justin Drake and Ethereum co-founder Vitalik Buterin warned that AI might break it before quantum computers.