If someone needs to prove something to a regulator or business partner, they can share a special “viewing key” that unlocks just that information, without handing over control of their money. A full viewing key can reveal incoming transactions and the details of standard outgoing payments to whomever it’s shared with. Disclosure becomes something the user grants selectively rather than something the network forces on everyone by default.

Interestingly, the idea predates Zcash by years. Bitcoin’s own creator, Satoshi Nakamoto, mentioned this style of cryptography in a 2010 online post, though they admitted they didn’t see how to apply it to Bitcoin at the time.

The numbers suggest people are actually using this feature, not just holding…