The art and science of code-making and code-breaking is driven both by the risk inherent in an adversary's ability to read an intercepted communication and the technology available to mitigate that threat efficiently and cost-effectively. This is true both for today's computer-driven cryptography and cryptanalysis and the simpler, yet no less vital codes and ciphers used in the past. In "Masked Dispatches: Cryptograms and Cryptology in American History,...