How encrypted messaging apps conquered the world

IT IS ILLEGAL for Americans to export weapons without a licence. You may not FedEx a ballistic missile to Europe or post a frigate to Asia. But in the 1990s the country’s labyrinthine arms-export controls covered something more unusual: cryptographic software that could make messages unreadable to anyone other than the intended recipients. When American programmers built tools that could encode a newfangled message, the email, their government investigated them as illegal arms dealers.