The Zcash infrastructure team has proposed a new privacy safeguard for users conducting cross-chain swaps through Near Intents. The design introduces one-time incoming viewing keys for each swap, addressing a potential vulnerability if quantum computers eventually become powerful enough to break current cryptographic protections.
Currently, multiple Zcash addresses can share the same underlying incoming viewing key. A sufficiently advanced quantum computer using Shor's algorithm could theoretically recover that key from a publicly exposed address and link payments across an entire account's history. By generating a unique viewing key for each swap, the proposal limits exposure to individual transactions.
How the System Works
Under the proposed design, each cross-chain swap receives its own incoming viewing key and refund address. If a quantum computer eventually breaks one publicly posted address, an attacker would only gain visibility into that specific swap rather than the account's broader payment history.
Critically, users' spending keys remain unchanged. Funds received through one-time addresses remain spendable from the same account, avoiding the need to create separate Zcash accounts for each transaction—a distinction that matters for both software and hardware wallet usability.
Solving Wallet Recovery Challenges
Creating new viewing keys for every swap introduces a technical challenge: wallet recovery would normally require scanning Zcash transaction history using every key ever generated.
Zakura proposes addressing this with private information retrieval (PIR). Public filters help determine whether a refund address received funds, while encrypted queries allow wallets to locate transactions without servers learning which address is being checked.
Real-World Usage Drives the Priority
The proposal addresses more than theoretical concerns. In September, Aurora Intents processed over $19 million across 1,718 swaps for a Zcash-denominated zkSNARKs auction, demonstrating meaningful demand for cross-chain routes into ZEC. This volume makes permanently published addresses a privacy issue worth addressing before quantum computing capabilities advance.
Compatible software wallets using open-source libraries could integrate the feature within weeks, with hardware wallet support expected later. The development reflects a broader shift in crypto security practices toward engineering defenses against quantum risks before practical attacks emerge.
