When Meiklejohn started college at Brown in 2004, she discovered cryptography. This branch of computer science appealed directly to her puzzle addiction—what was an encryption system, after all, but another secret language demanding to be deciphered? There was a maxim in cryptography, often referred to as Schneier’s law after the cryptographer Bruce Schneier. It asserted that anyone can develop an encryption system clever enough that they can’t themselves think of a way to break it. Yet, like all the best conundrums and mysteries that had fascinated Meiklejohn since childhood, another person with a different way of approaching a cipher could look at that “unbreakable” system and see a way to crack it and unspool a whole world of decrypted revelations. Studying the science of ciphers, Meiklejohn began to recognize the importance of privacy and the need for surveillance-resistant communications. She was not quite a cypherpunk: The intellectual appeal of building and breaking codes drove her more than any ideological drive to defeat surveillance. But like many cryptographers, she nonetheless came to believe in the need …