July 31, 2021
10:00 am — 4:00 pm
Carpenter’s Hall, Philadelphia
Going into the Revolution, Americans were at a huge disadvantage to the European powers when it came to cryptography, many of which had been using secret offices where sensitive letters were opened and deciphered by public officials for centuries. It was not uncommon for the messages of Revolutionary leaders and American diplomats to be intercepted and read by their enemies, both at home and abroad. To combat this, many of our founding fathers and key generals relied heavily on the use of cryptography. Cryptography is split into two ways of changing the message systematically to confuse anyone who intercepts it: these are codes and ciphers. Many people believe, and use, the word code to mean the same thing as cipher, but technically they are different.
A code is a way of changing the message by replacing each word with another word that has a different meaning. For example, “Burn the City” could become “Take the rubbish” where the word “burn” is represented by the codeword “take”, and similarly for “city” and “rubbish”. Using codes requires a codebook, which contains all such codewords. Considering the large number of words in most languages, this is normally quite a large book, making the use of codes rather cumbersome (it is a bit like a French dictionary, giving the translation to and from the codeword). However, they can be used to encode key words in a message. Consider the message “Kill him as soon as possible”. With a simple change of a single word this becomes “Meet him as soon as possible”, which may pass through security detection without being noticed. So, although potentially hard to use, a simple code can be very effective, since even if the message is intercepted, they can be used so that the code reads as an innocent or unrelated topic.
Ciphers, on the other hand, convert the message by a rule, known only to the sender and recipient, which changes each individual letter (or sometimes groups of letters). Ciphers, are significantly easier to use than codes, since the users only have to remember a specific algorithm (a mathematical word for process) to encrypt the message, and not a whole dictionary of codewords. The major setback for ciphers compared to codes is that if someone finds a message that has been encrypted using a cipher, the output is almost certainly going to be a random string of letters or symbols, and as such the interceptor will know straight away that someone wanted to hide this message.
Cryptography was no parlor game for the idle classes, but a serious business for revolutionary era statesmen who, like today’s politicians and spies, needed to conduct their business using secure messaging. Codes and ciphers involved rearranged letters, number substitutions, and other methods. What follows are some of the most common cyphers used by George Washington and the Continental Army.
As the Spy Master, I will recruit and train spies and provide them with hands on exercises to practice their spy craft before being sent into the British encampments to collect intelligence. We will present several codes and cyphers for the participants to encode and decode messages, “dead drop” will be established in the environs of Carpenters Hall for our spies to exchange messages with other spies, and we will have discussions of famous spies in the George Washington’s and General Howe’s employ.