Zcash developers plan a fix to keep ZEC swaps private from future quantum computers

Ordinary computers can’t 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 theroretically work backward from the address to the key.

That’s the real threat hanging over Satoshi-era bitcoin, whose public keys already sit onchain for anyone to copy. Last week, Google said its Willow quantum chip had produced near-perfect versions of one of the components such an attack would burn through, a step toward a machine powerful enough to try it.

Quantum computers capable of that are still likely years away (and no one has a firm timeline for when one could be built), but it’s a problem developers across the industry are rushing to solve.

One key for every swap

Zcash’s architecture gives it a problem of its own. A Zcash wallet can generate many addresses that look unrelated to each other, but they normally share one viewing key.

An attacker who cracks that key from a single published address could link every payment the account ever received and read the amounts and the private notes, or memos, attached to them.

Spending takes a separate key, so the funds themselves would stay safe. Zakura’s fix gives each swap its own viewing key and leaves the spending key with the user’s main account. An attacker who someday cracks a refund address on NEAR would see only the payments tied to that one swap.

The design also deals with a practical snag.