Zcash Dev Unveils Quantum-Resistant Shielded Swap Fix

Zcash Developer Zakura Proposes Fix to Stop Quantum Computers Linking Shielded Swaps

Zcash infrastructure developer Zakura has proposed a new wallet feature designed to reduce a future privacy risk from quantum computing: the possibility that a single publicly exposed Zcash address could allow an attacker to link a user’s historical shielded payments.

Zcash’s shielded transactions are built to hide the sender, recipient, and amount. However, Zcash wallets typically rely on a single incoming viewing key for a shielded account—a key that helps the wallet detect and decrypt incoming payments across all addresses tied to that account.

According to Zakura’s proposal, that design could become a privacy liability in a post-quantum world. Zakura says a single published Zcash address could let a future quantum attacker link every payment a wallet has ever received, if the cryptography protecting that exposed address were eventually broken.

The proposed change focuses on ZEC swaps routed through NEAR Intents, a pathway that has already seen substantial usage. Zcash Open Development Lab CEO Josh Swihart previously said around $600 million to $700 million had flowed through Zcash’s NEAR Intents route by May.

Zakura’s fix would derive a separate incoming viewing key for each address that has to be published, while leaving the wallet’s existing spending key unchanged. In practice, this means that if a quantum-capable attacker were ever able to break one posted swap address, the information exposure would be limited to payments sent to that one address, rather than enabling links across a broader transaction history. As described in a social media thread, “If a quantum computer ever breaks a posted swap address, it will not be able to link this to any other transaction.”

The proposal also attempts to avoid degrading the user experience during wallet recovery. Deriving and tracking many one-time keys could slow down restores from a seed phrase, so the design uses private information retrieval to look up NEAR payouts in a way that allows a wallet to query a server without revealing which addresses it is searching for.

The broader context is Zcash’s ongoing planning for post-quantum security. Developers have targeted January 2027 for introducing post-quantum signature instructions that would allow transparent Zcash transactions to use hash-based signatures. That effort is aimed at protecting spending authorization, while Zakura’s latest design is focused specifically on preventing historical shielded payments from becoming linkable through an exposed address.

Importantly, the proposal addresses a future risk tied to potential advances in quantum computing, rather than an active quantum vulnerability today.