Zakura Designs Per-Swap Private Keys for ZEC to Anticipate Quantum Computing Threats

Zcash developers, through the Zakura project, are preparing a new safeguard for ZEC privacy transactions that pass through the NEAR Intents service. The proposal emerged as a response to the potential threat of quantum computers which, if realized, could link users' private transactions to their originating wallets. The move is crucial because privacy is Zcash's main selling point in the digital asset market.

NEAR Intents itself is a service that lets users swap tokens across chains. When someone swaps private ZEC for USDC, the service publishes one of the user's Zcash addresses on the public NEAR chain. The aim is to allow leftover funds to be returned. The address remains visible even after the transaction is complete and no refund is made. This is the gap that has drawn attention.

On conventional computers today, a public address leaks no information. Each Zcash address contains a public key built from the wallet's viewing key, the secret used to detect incoming payments. The process relies on one-way elliptic curve mathematics, similar to what protects bitcoin and ether wallets. However, a sufficiently large quantum computer running Shor's algorithm—a method published in 1994—could theoretically reverse the calculation and derive the private key from the public address.

The threat is not imaginary. Last week, Google announced that its Willow quantum chip had produced a near-perfect version of one of the components needed for such an attack. Although a quantum computer truly capable of carrying out such an attack is still estimated to be years away, developers across the industry are racing to find solutions. Bitcoin from the Satoshi era is also said to have a similar vulnerability because its public keys are already stored on-chain and can be copied by anyone.

Zcash's architecture creates its own problem. One wallet can generate many seemingly unrelated addresses, but they all share a single viewing key. If an attacker manages to crack that key from one published address, they can link every payment the account has ever received, read the amounts, and even the private notes or memos attached to them. The key for spending funds is separate, so the funds themselves remain safe. However, transaction privacy can collapse.

Zakura offers a solution by providing a separate viewing key for each swap, while the spending key stays in the user's main account. As a result, an attacker who cracks the refund address on NEAR will only see payments tied to that one swap, not the wallet's entire history. This approach significantly reduces the attack surface.

The design also addresses a practical constraint. A wallet that has performed hundreds of swaps will hold hundreds of keys. Restoring a wallet from backup means scanning the entire Zcash chain with every key, which is burdensome. Zakura overcomes this with a database that can be queried privately using a private information retrieval technique. The wallet asks where its refund funds landed, and the database answers without knowing which address was queried. Privacy is thus preserved while recovery efficiency is maintained.

Zakura states that wallets built on their open-source libraries, including Vizor, can add this feature within the coming weeks. Hardware wallets will follow once their firmware supports it.

To date, no quantum computer has been proven capable of recovering such keys. However, Zakura's move shows that the race against the quantum threat in crypto is increasingly real. For Indonesia, this development is relevant given the growing number of retail investors holding crypto assets, including those who prioritize privacy. Domestic regulators and industry players need to pay attention to post-quantum security standards so as not to fall behind in protecting user data and assets.

Looking ahead, the question is how quickly quantum-resistant solutions can be widely adopted. If the January 2026 target is met, Zcash could become a pioneer in post-quantum privacy. However, challenges remain: hardware wallet adoption, user awareness, and the readiness of supporting infrastructure. Without adequate education, this advanced feature may go untouched by the majority of users.