End-to-end encryption is a way to keep messages private. It’s sometimes used by apps, which basically turn those messages into unintelligible chunks of data as soon as a user hits “Send.” The idea is that no one, except sender and recipient, can access that message. Not hackers, not third parties, not even the app platform itself. And you need special “keys” stored on an individual device to decrypt it. But many messaging platforms don’t have this kind of encryption, and some provide it only as an option. Kimberly Adams of “Marketplace Tech” spoke with Matthew Green, a professor at the Johns Hopkins Information Security Institute, about why more apps don’t have end-to-end encryption by default.