Zakura developer Adam Tucker discussed post-quantum unlinkable swaps that do not require network upgrades. In the Zcash network, shielded transactions conceal the sender, recipient, and transaction amount. Each such account is assigned a single incoming viewing key linked to all account addresses. The wallet uses this key to locate and decrypt payments received at any of these addresses.
A typical modern computer cannot compute this key knowing only the address. However, theoretically, a powerful quantum computer using Shor’s algorithm could break certain modern cryptographic schemes. The developer warns that a hypothetical attacker could learn the amount and accompanying message for each payment, as well as link all these transactions together.
According to Tucker, the greatest risk lies with swaps via NEAR Intents—a cross-chain asset exchange service. When conducting a swap using ZEC, the user’s shielded address is recorded on NEAR’s public blockchain as the return address, regardless of whether a refund actually occurs. Even though these addresses may appear different, they all belong to the same account; therefore, if one address is compromised, information about all other addresses will be exposed. By May, between $600 million and $700 million had flowed through NEAR Intents on the Zcash network.
“Until the Tachyon upgrade is implemented, there are significant risks: publishing even one ‘shielded’ address would allow a quantum computer to link all payments ever received at that address and identify other addresses using the same key,” said Tucker, promising that the Zcash upgrade will ensure transaction privacy.
In Zakura, it was proposed to create a separate view key for incoming transactions for each address that needs to be published—while keeping the primary spending key unchanged. If a quantum computer compromises one published address, it will gain information only about payments to that specific address and will not be able to link them to other transactions.
Recently, Zcash private coin co-founder Eli Ben-Sasson stated that quantum resistance should become a standard feature of all cryptocurrencies. However, Ben-Sasson warned that investors will not want to switch to more secure protection if it requires complex account manipulations.