No
matter how a message was transmitted, wigwag, telegraph, or
written, for security purposes, it was often encoded or enciphered.
A code changes a word or phrase into a different word, phrase,
or number group; a cipher substitutes each individual letter
for a different letter, number, or symbol. Below are two examples
of such systems.
Although entitled Cipher for Telegraphic Correspondence, this book is actually a code book. It was used by Union General Joseph Hooker’s code clerk and is one of the few books whose provenance is known. Important names, places, and military terms have two different code names.
The
Confederate cipher cylinder is one of only two surviving cipher cylinders. Using
a Vigenere square, plain text letters and their corresponding
cipher letters
are indicated by the position of the pointers. Each system has its
benefits and disadvantages, but both offered an excellent level of
security.