Zakura Suggests Per-Swap Viewing Keys for Zcash
Adam Tucker, an engineer at Zakura, has proposed a wallet-level modification for Zcash. This change would generate a unique, one-time incoming viewing key for each Zcash swap processed via NEAR Intents. The primary goal is to minimize the extent of potential linking by a future quantum attacker, should a shielded swap address become publicly visible on another blockchain. This proposal is noteworthy because it maintains spending authority with the original account and addresses a theoretical risk.
Proposed Changes Explained
The concern arises with swaps utilizing NEAR Intents, where a Zcash wallet might publish a shielded refund or recipient address on NEAR’s public chain. Typically, diversified addresses originating from a single account share a common incoming viewing key. According to Tucker’s technical explanation, a sufficiently powerful quantum computer employing Shor’s algorithm could derive this shared key from one exposed address, thereby linking all payments received across that account.
Zakura’s proposed design aims to compartmentalize this exposure. Key aspects, as outlined by the company, include:
- A unique, one-time incoming viewing key would generate for each individual swap.
- The original account would retain spending authority, allowing the spending of funds without requiring a new account for each swap.
- The swap index would record in an encrypted memo.
- Public filters combined with Private Information Retrieval would help locate relevant NEAR payouts, without disclosing the queried address to the server.
- Software wallets that use Zakura’s open-source libraries, including Vizor, are expected to integrate this feature in the coming weeks.
- Hardware wallet compatibility would necessitate firmware updates.
Scope of the Proposal
If a future attacker were to compromise the key associated with a single published address, the exposure would be confined to payments sent to that specific address. The wider receiving history of the account would remain private. This targeted approach is the core of the design and represents a more focused mitigation than a complete post-quantum Zcash migration.
It’s important to clarify two points: First, this risk remains theoretical, as no known exploit against shielded transactions has been demonstrated. Second, recovering an incoming viewing key does not grant an attacker the ability to spend funds; therefore, this proposal doesn’t impact spend authorization. Furthermore, this initiative doesn’t render Zcash universally quantum-safe, nor does it replace ongoing post-quantum signature research like Project Epoch.
The Significance of Wallet-Layer Linkability
This mitigation directly addresses the “harvest-now-decrypt-later” threat, where adversaries collect exposed data today with the intent to decrypt it once quantum computing becomes available. This same concern is driving national PQC migration deadlines. This is a privacy enhancement, distinct from NIST FIPS 203/204/205 signature migration and separate from the security of spending keys that govern fund movement. Other networks are exploring more fundamental changes, such as Starknet’s quantum-resistance plan.
For further information on post-quantum Zcash developments and broader crypto migration efforts, please refer to our ongoing coverage at QNews.