Zcash Developers Propose Per-Swap Keys to Guard ZEC Privacy Against Future Quantum Computers

Zakura proposes a separate key for each ZEC swap

The team behind Zakura, a newer version of the software that runs the Zcash network, has proposed a change to protect the privacy of ZEC swaps made through NEAR Intents. Zcash is a cryptocurrency designed to make payments private.

NEAR Intents is a service that lets users swap tokens across different blockchains. The proposal, described in a new engineering post, would give every ZEC swap made through the service its own private key.

The aim is to close a gap that a future quantum computer could use to link a user's private ZEC transactions to their wallet.

How a refund address creates a privacy gap

When someone swaps private ZEC for USDC through NEAR Intents, the service posts one of the user's private Zcash addresses on NEAR's public chain. It does this so it knows where to send back any unused ZEC. USDC is a stablecoin, a crypto token meant to hold a steady value.

That address is published as soon as the deposit lands and stays there even if the swap completes and no refund is ever needed.

Such addresses reveal nothing on today's computers. Each Zcash address carries a public key built from the wallet's viewing key — the secret a wallet uses to spot payments sent to it — using one-way elliptic-curve math similar to that used for bitcoin and ether wallets.

Ordinary computers cannot run that math in reverse. But a large enough quantum computer running Shor's algorithm — a method published in 1994 for exactly that job — could theoretically work backward from the address to the key. The CoinDesk report notes that quantum computers capable of this are still likely years away, and that no one has a firm timeline for when one could be built.

Key points

• Zakura proposes a separate viewing key for every ZEC swap made through NEAR Intents.
• The goal is to limit how much payment history a future quantum computer could uncover from a refund address posted on NEAR's public chain.
• The proposal would keep spending keys with users while using private information retrieval to help wallets locate refunds without revealing which addresses they check.
• Zakura says compatible software wallets could adopt the open-source feature within weeks.
• Zcash developers have a January target for quantum-resistant payments.

What the Zakura engineering post says

Zakura's engineering post outlines two parts to the fix. It would assign a separate viewing key to each swap, so cracking one published address would not expose a wallet's wider payment history. Zcash's architecture currently creates this problem because a wallet can generate many addresses that look unrelated but usually share one viewing key.

The proposal would also keep spending keys with users. Spending keys are the secrets that let a user move funds. To help wallets locate refunds without revealing which addresses they are checking, the design uses private information retrieval.

What is confirmed

• The team behind Zakura published an engineering post proposing the change.
• NEAR Intents posts a user's private Zcash refund address on NEAR's public chain when a ZEC swap is made.
• Zakura says compatible software wallets could adopt the open-source feature within weeks.
• Zcash developers have set a January target for quantum-resistant payments, according to the report.

What is still unclear

How quickly wallets will adopt the feature, and whether the January target for quantum-resistant payments will be met, are not confirmed. The source does not say when, or whether, the proposal will be fully implemented. The threat itself is theoretical at this stage: quantum computers able to reverse the math are still likely years away, and no firm timeline exists for building one.

Why it matters for Zcash users

Zcash is built around private payments. If a refund address left on a public chain could later be linked back to a user's viewing key, that could weaken the privacy the network is meant to provide. The proposal is one attempt to reduce that risk without changing how users hold their spending keys.

Sources

• CoinDesk