CRYPTOGRAPHY: The Science of Secret Writing

Manual of the fundamentals of secret communication which presents simply a few historical notes on the science, a science which dates back to ancient Egypt, and then outlines the basic elements and gives illustrations and problems for solution. The author was in the Military Intelligence in the last war. The two main principles of cryptography,-transposition and substitution, with various devices, keys, variations; codes, briefly; the prerequisites of a cryptanalyst; more problems. Courses are being given to civilians; here's a chance to see. If you are eligible.