Key facts

• Zakura wants every ZEC swap routed through NEAR Intents to receive its own viewing key.
• The goal is to prevent a refund address posted on NEAR’s public chain from exposing a user’s wider Zcash payment history to a future quantum computer.
• Spending keys would remain with users, while private information retrieval would let wallets find refunds without revealing which addresses they are checking.
• Compatible wallets could adopt the open-source feature within weeks, ahead of a January target for quantum-resistant Zcash payments.

Zcash developers are preparing a privacy upgrade for cross-chain swaps that aims to close a subtle but consequential leak: the refund address left on a public blockchain when a ZEC trade is routed through NEAR Intents. The proposal, developed by the team behind Zakura, would give every swap its own viewing key, so a single public address cannot become a thread that pulls on a user’s wider payment history. The concern is not only immediate exposure. It is the possibility that data recorded today could be decoded by a sufficiently powerful quantum computer later.

The design is aimed at the intersection of two systems with very different privacy models. Zcash offers shielded transactions that can hide sender, receiver and amount, while NEAR is a public blockchain where addresses and transaction data are visible by default. When a user swaps ZEC through NEAR Intents, the mechanics can require a refund path on the NEAR side. That refund address may be posted publicly, and if it can be linked to a broader Zcash wallet, it can reveal more than the single trade.

Why a refund address can expose more than one swap

Cross-chain swaps are rarely a single, clean event. A trade may be filled in parts, delayed, cancelled or adjusted by solvers that compete to execute the user’s intent. Each of those outcomes can create a need for a refund or a residual transfer. In an intent-based system, users express what they want to achieve, and solvers compete to deliver the result. That model can improve execution, but it also creates public artifacts on the settlement chain.

If a public refund address is reused or linked to a single user, an observer can begin mapping activity around that address. In a transparent blockchain environment, the observer sees the refund, the timing and any related transfers. The danger is that this public data may eventually be connected to shielded Zcash activity. A user who values privacy may keep their trading life separate from their everyday wallet, but a refund address can quietly bridge those worlds. Once the bridge exists, it can be difficult to dismantle.

Zakura’s answer is to reduce the blast radius. Instead of letting one viewing key or one address relationship cover many swaps, the proposal assigns a separate viewing key to each ZEC swap made through NEAR Intents. That means the information needed to resolve one trade does not automatically unlock the history of every other trade. The privacy boundary becomes the individual swap rather than the user’s entire wallet.

How Zcash viewing keys fit into the design

Zcash’s shielded pool relies on a distinction between spending authority and visibility. A spending key controls funds and authorizes transactions. A viewing key lets a holder see transaction details without being able to spend the money. That separation is central to Zcash’s privacy model because it allows selective disclosure: a user can share visibility with an auditor, exchange or wallet service without handing over control of the assets.

The proposal uses that separation carefully. A per-swap viewing key would give the relevant swap process enough visibility to handle refunds and confirmations for that trade, but not enough to expose the user’s broader payment graph. If the refund address is later examined, or if a future quantum computer attempts to break data recorded on public chains, the exposed information should be limited to the swap at hand. The user’s spending keys stay where they belong: with the user.

That last point matters. Privacy fixes can fail if they require users to surrender control to a custodian or a centralized service. Zakura’s design is described as keeping spending keys with users while using scoped viewing keys for the swap workflow. The approach tries to preserve self-custody without forcing users to choose between convenience and privacy. It also gives wallets a clear rule: derive or assign one viewing context per swap, then discard or isolate it when the trade is complete.

Spending keys stay with users

The proposal does not ask users to move their ZEC into a special pool or to trust a third party with spending authority. That is significant because cross-chain swaps often involve temporary custody, wrapped assets or bridge contracts. Each of those steps can create new data trails. By keeping spending keys with users and limiting the visibility granted to the swap process, the design attempts to prevent a refund workflow from becoming a permanent surveillance hook.

For wallets, the challenge is practical. A wallet must be able to detect when a refund arrives, confirm the amount and update the user’s balance without scanning or revealing every address in the user’s wallet. If the wallet simply asks a server about a list of addresses, the server learns which addresses belong to the user. That is where private information retrieval comes in.

Private information retrieval and the refund lookup problem

The harder problem is not creating a viewing key. It is helping a wallet find a refund without telling the world which addresses it is checking. A wallet that queries a public or semi-public service for refund status can leak metadata even if the underlying transaction is shielded. The query itself can reveal a connection between the user and an address, especially if the wallet checks the same address repeatedly or in a predictable pattern.

Private information retrieval, or PIR, is designed to solve that kind of lookup privacy problem. In general terms, PIR lets a client retrieve an item from a database without the server learning which item the client requested. Applied to Zcash swaps, a wallet could use PIR to search for refunds or related records without disclosing the specific addresses it is monitoring. The server can return the needed information, but it does not learn which refund address the wallet cares about.

That combination is important. Per-swap viewing keys limit what can be learned if a refund address is exposed. PIR limits what can be learned from the act of checking for refunds. Together, they address both the data that sits on public chains and the metadata that wallets generate while trying to use that data. The proposal is therefore not just a key-management change. It is a broader attempt to keep swap operations private at the wallet, network and settlement layers.

Quantum risk and the harvest-now problem

The quantum angle makes the proposal more urgent than it might first appear. Quantum computers powerful enough to break widely used public-key cryptography are not yet available, but privacy engineers must plan for a future in which they are. One common threat model is harvest now, decrypt later. An adversary records public data today and waits for better decryption tools tomorrow. If a refund address or related transaction data can be linked to a user’s Zcash history, that recorded data could become more dangerous over time.

Zcash already relies on advanced cryptography, including zero-knowledge proofs and elliptic-curve constructions. A large-scale quantum computer could threaten some of the assumptions behind those systems. The Zcash ecosystem has been working toward quantum-resistant payments, with a January target cited for that work. Zakura’s proposal is narrower, but it fits the same defensive logic: reduce the amount of linkable information that exists on public chains now, before future decryption changes the calculus.

The proposal does not claim to make Zcash fully quantum-proof in one step. It focuses on the swap path and the refund address, which are practical weak points for users who move between shielded ZEC and public cross-chain systems. By giving each swap its own viewing key, the design tries to ensure that a future quantum computer cannot use one public address to reconstruct a user’s entire payment history.

Timing, wallet adoption and the January target

Zakura says compatible software wallets could adopt the open-source feature within weeks. That timeline is faster than a consensus-level change would typically allow because the work is aimed at wallet and swap-tooling behavior rather than requiring every participant in the Zcash network to upgrade at once. Wallets that support ZEC swaps through NEAR Intents would need to implement the per-swap viewing key logic, integrate PIR-based refund lookups and test the flow against real swap outcomes.

The timing is deliberate. Zcash developers’ January target for quantum-resistant payments gives the ecosystem a broader deadline, but users do not need to wait for a complete network overhaul to benefit from better swap privacy. If wallets can ship the feature earlier, they can reduce the linkability of refund addresses while the longer-term cryptographic work continues. The open-source approach also allows wallet teams to review the design, adapt it to their architectures and avoid a single vendor controlling the privacy layer.

Cross-chain swap privacy is likely to become a bigger issue as intent-based systems grow. Users are drawn to these systems because they can move assets across chains without managing every step manually. But convenience often creates metadata. A public refund address, a repeated solver, a predictable timing pattern or a wallet query can all become pieces of a puzzle. The Zakura proposal treats each of those pieces as a potential leak and tries to constrain what any one piece can reveal.

The next milestone is wallet-level testing and integration. The proposal’s effectiveness will depend on how well wallets isolate viewing keys, how reliably PIR queries hide user intent and whether swap solvers can complete refunds without introducing new public links. The design gives the Zcash ecosystem a concrete way to keep ZEC swaps private from future quantum computers while preserving self-custody and the practical refund workflows that cross-chain users depend on.

Source:Coindesk News