Despite its reputation as a language only of spies and hackers, cryptography plays a critical role in our everyday lives. Though often invisible, it underpins the security of our mobile phone calls, credit card payments, web searches, internet messaging, and cryptocurrencies?in short, everything we do online. Increasingly, it also runs in the background of our smart refrigerators, thermostats, electronic car keys, and even the cars themselves. As our daily devices get smarter, cyberspace—home to all the networks that connect them—grows.