Zcash Plans 1 Key per Swap to Limit Quantum Risks to Private ZEC Payments

Zcash developers at Zakura are proposing a privacy improvement that would assign a separate viewing key to every ZEC swap made through NEAR Intents. The change aims to prevent a future quantum computer from using one exposed address to uncover a user’s wider payment history. The proposal addresses a specific weakness in cross-chain swaps, where a private Zcash address can become publicly visible on another blockchain. Although powerful quantum computers capable of breaking today’s cryptography have not been demonstrated, developers are preparing safeguards before such technology becomes practical.

Why ZEC Swaps Face Quantum Risks

NEAR Intents enables users to exchange tokens across different blockchains. When someone swaps shielded Zcash (ZEC) for USDC, a publicly accessible address may be posted on NEAR’s blockchain so the service can return unused funds if a refund is necessary.

The concern is that this address can remain visible even when no refund occurs. Under Zcash’s current key structure, multiple addresses can share a viewing key, which allows a wallet to identify incoming payments and read associated transaction details.

Today’s conventional computers cannot feasibly reverse the elliptic-curve mathematics underpinning many cryptocurrency keys. However, a sufficiently powerful quantum computer running Shor’s algorithm could theoretically undermine that protection.

Google’s Willow quantum chip has demonstrated advances in quantum computing, but it has not demonstrated the ability to recover cryptocurrency private keys. The timeline for a machine capable of such attacks remains uncertain.

One Viewing Key for Every Swap

Zakura’s proposed solution separates the viewing key used for each swap while leaving the user’s main spending key unchanged. This limits the potential damage if a publicly exposed swap address becomes vulnerable.

If an attacker eventually recovers one swap’s viewing key, the information exposed should be restricted to payments associated with that key rather than the account’s entire transaction history. The funds themselves remain protected by a separate spending key, although this design alone does not eliminate every quantum-related risk.

The approach introduces a practical challenge: wallets may need to manage hundreds of viewing keys and scan the blockchain to restore transaction histories after a backup recovery.

Zakura proposes using private information retrieval (PIR) to address that problem. The technique allows a wallet to request relevant records from a database without revealing which specific addresses it is checking.

Key implications include:

• Reduced exposure: A compromised viewing key reveals a narrower set of transactions.
• Wallet complexity: Managing multiple keys increases recovery and synchronization demands.
• Privacy-preserving lookups: PIR can help prevent database operators from linking addresses through wallet queries.

Wallet Rollout and Quantum Roadmap

Zakura says wallets 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.

The proposal is separate from the broader Zcash quantum-resistant upgrade, for which developers have outlined a January target for post-quantum payment protections. That target is not a confirmed network activation date.

Conclusion

Zakura’s one-key-per-swap proposal aims to contain the privacy damage a future quantum breakthrough could cause to ZEC users who transact through NEAR Intents. Its effectiveness will depend on implementation, wallet support and secure key management. It is a targeted privacy measure, not proof that Zcash is fully protected against quantum attacks.