Hassan Maishera
TL;DR
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Zakura developers proposed a change to limit potential quantum-related privacy risks when swapping ZEC through NEAR Intents.
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The service publishes a Zcash refund address on NEAR’s public blockchain, even when no refund is required.
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A sufficiently powerful future quantum computer could theoretically derive viewing-key information from an exposed address.
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Assigning a separate viewing key to each swap would limit potential exposure to that swap rather than a user’s wider payment history.
Public Refund Addresses Create a Future Privacy Concern
Developers behind Zakura, a newer implementation of Zcash’s network software, have proposed a change intended to protect users’ transaction privacy against a potential future quantum attack.
The concern involves NEAR Intents, a service that enables swaps between assets on different blockchains.
When a user exchanges shielded ZEC for an asset such as USDC, the service publishes a Zcash refund address on NEAR’s public blockchain. That address tells the system where to return unused ZEC.
The address becomes public when the deposit arrives and remains visible even if the swap completes successfully without a refund.
Publishing the address does not currently allow ordinary computers to uncover the user’s private payment history. The concern is that sufficiently advanced quantum hardware could eventually change that.
Zcash addresses contain public-key information protected by elliptic-curve cryptography. Conventional computers cannot feasibly reverse the relevant mathematical operations to recover secret key material. However, a sufficiently powerful quantum computer running Shor’s algorithm could theoretically undermine that protection.
Zcash’s wallet structure makes the potential consequences significant. A single account can generate many addresses that appear unrelated but share a viewing key.
Under the attack scenario described by Zakura, recovering viewing-key information from one exposed address could reveal payments associated with the wider account, including amounts and attached memos.
That is a privacy risk rather than an automatic route to stealing funds. Spending requires a separate key, which would not be exposed through the viewing-key attack described.
No quantum computer has demonstrated the ability to perform this recovery, and the timeline for such a machine remains uncertain.
Separate Viewing Keys Would Limit Exposure to Individual Swaps
Zakura’s proposed solution is to give each NEAR Intents swap its own viewing key while retaining spending control with the user’s main account.
The aim is to prevent one publicly recorded refund address from becoming a route into a much larger transaction history.
If a future attacker recovered the viewing information associated with that address, the exposure would be limited to payments linked to the individual swap.
The approach therefore reduces the potential scope of a future privacy breach. It does not, by itself, make the exposed address’s cryptography quantum-resistant.
Using separate viewing keys introduces an operational challenge. A wallet used for hundreds of swaps could accumulate hundreds of keys. Restoring it from a backup could then require scanning the Zcash blockchain repeatedly to locate relevant payments.
Zakura proposes addressing this with a database that wallets can query using private information retrieval.
The technique would allow a wallet to ask where its refunds arrived without revealing to the database which addresses it is checking.
That could make recovery more practical while preserving privacy during the lookup process, helping avoid a trade-off between stronger isolation and cumbersome wallet restoration.
Wallet Support Could Arrive Before Broader Quantum Upgrades
Zakura said wallets built using its open-source libraries, including Vizor, could introduce the feature in the coming weeks.
Hardware wallet support would follow once compatible firmware becomes available. That schedule would place the proposed protection ahead of the January target Zcash developers set earlier this month for quantum-resistant payments.
For now, the proposal is a preventive measure: reducing the amount of private transaction history that could become exposed if quantum computers eventually overcome today’s cryptographic protections.
