For all the promise of blockchain, there’s a problem that comes with treating all transactions as public information: some of that stuff is just nobody’s business. But with Zcash, a cryptocurrency cofounded by Alessandro Chiesa, transactions can be not only secure but as anonymous as handing someone a $20 bill from your wallet.

That’s because Zcash employs a cryptographic protocol called a succinct zero-knowledge proof (see “10 Breakthrough Technologies 2018: Perfect Online Privacy”)—that is, an efficient way to convince both parties to a transaction that something is true without divulging any other information.

Zcash has huge implications for transactions that might otherwise reveal a buyer’s or seller’s location, medical information, or other private data. It allows people to do transactions online without risking their privacy or exposing themselves to identity theft. Zcash, which Chiesa launched four years ago, now has a market cap of over a billion dollars.

—Dan Solomon