Herbert Yardley was considered one of the most controversial figures in American cryptology. During his career, he served as a code clerk with the State Department, a military intelligence officer with the AEF, and as the initial chief of MI-8 - the United States’ first permanent centralized cryptanalytic organization. When MI-8 was closed down in 1929, Yardley published an unauthorized and revealing book, The American Black Chamber, about the activities of MI-8.

While this was Yardley’s best-known work, the following five stories are taken from another Yardley book, YARDLEYGRAMS, published in 1932. The purpose of the book was to teach the reader how to decipher cryptographic messages.

Help cipher expert Alan Crossle teach his nephew Charles how to use different cipher systems to crack codes. See if you can solve these super-tough ciphers without looking at the solution.