Professor Isabel Ruffell and I have been teaching an Honours and Postgraduate course called Ancient Technology in Context ever since I arrived at Glasgow, back in the autumn of 2016. Last semester, we taught the fifth (!) iteration of it, and for the final session before the Christmas break, I thought I would try something a little different. Since that week’s lecture was on Information Technologies (i.e. the development of ancient Greek and Latin writing and all the things ancient Greeks and Romans liked to use it for), I thought a suitable topic for the accompanying seminar would be ancient codes and ciphers.
A Quick Introduction to Ancient Codes and Ciphers in Theory
Cryptography (kryptos – ‘hidden from, secret’, graphein – ‘to write’) is the practice of securing communication by enciphering rather than concealing the message, so the original message, the ‘plaintext’, is converted into an encrypted message, the ‘ciphertext’. Two types of ciphers were used in the ancient world, transposition ciphers and substitution ciphers.
For a transposition cipher, the normal sequence of letters of plaintext is rearranged (the alphabetic letters are not normally replaced with other letters, numbers, or ciphers), while for a substitution cipher the letters of plaintext are substituted with other letters, characters, or symbols not necessarily found in the original text, and the sequence of ciphertext letters used for the encryption and decryption is known as a ciphertext alphabet. The oldest ancient Greek method of secret communication in this style was, perhaps not surprisingly, used by the Spartans. They wrote their messages on parchment wrapped around rods (the Greek for rod/baton is skytale, hence Spartan Scytale), resulting in a transposition cipher. The sender and the recipient would have the same sized rods, and so can wrap the parchment around the rod and see the letters in the right order (Plutarch, Lysander 19; Aulus Gellius, Attic Nights 17.9.6-15; Ausonius, Epistles 28.23-27).
Then there are the substitution ciphers, the two most famous the Polybius Square and the Caesar Shift. For the Polybius Square, while Polybius did not invent this method (rather he borrowed it from the otherwise unknown Cleoxenus and Democleitus), he did make it famous by including it in his Histories (10.7.45-47). Each letter corresponds to numbers so A = 1,1, B = 1,2, C = 1,3 and so on (this was originally done using fire signals, so the shorter the message the better).
Then there is the Caesar Shift. Julius Caesar created a simple substitution cipher, changing the order of the letters of the alphabet by ‘shifting’ them four places, so A = D, B = E and so on (Suetonius, Caesar 58.6). This method was also used, with variations, by his adopted son Augustus (Suetonius, Augustus 88).
Alternatively, steganography (steganos – ‘covered, concealed’, graphein – ‘to write’) is the practice of concealing a message within another message, image, or object without giving any outward sign that a message is hidden in it, and the hidden message is thus a steganogram. These messages are not necessarily written in code because the physical concealment is intended to provide security and secrecy, although for an extra level of security you could potentially write in code and then hide the message in some way. While the ancient Greeks and Romans used plenty of hiding places for their secret communications (if you can imagine it, they used it, and some of them are rather unsavoury), they also used invisible ink made from various different substances such as milk, gallnuts crushed in water, or moistened flax.
A Quick Introduction to Ancient Codes and Ciphers in Practice
I covered the different types briefly in the lecture, provided instructions on how to do them, and asked the students to prepare short messages that they would like to encode, so when the time came for the seminar, we could jump right in. I set up different stations around the room so students could choose whether they wanted to encrypt their messages with the Polybius Square or Caesar Shift ciphers, write in different types of invisible ink (I brought in lemon juice and milk, and several different types of paper), or attempt to make and use a Spartan Scytale (I brought in different sizes of cylinders – kitchen roll, toilet roll etc.). There was enough time that each student could attempt more than one, and some eager beavers tried all five of them. Each student encrypted their message, then passed it to a classmate to see if they could decode it (the messages written in invisible ink were heated up later to make the inks visible).
What I hoped the students would get out of this seminar was a deeper understanding of the practicalities of writing in this way: Is it easy or hard to encrypt a message via one of the transposition or substitution ciphers? Is it quick or does it take time? Are different types of message easier or harder to encrypt or decode? How secure are these methods? How quickly could they be decoded? I also asked them for their feedback, both on using the codes and ciphers, and on the format of seminar.
According to Charlie, ‘Yesterday I was somewhat struggling to understand how some of the coding systems discussed work, but today being able to actually try and recreate them helped me tremendously. I also really appreciated today’s seminar because it gave me and the rest of my cohort the opportunity to do something creative and hands on, which thoroughly engaged my attention’. Alice agreed. ‘The invisible ink was really cool, I remember doing it when I was younger so it was great to get to do it again. It was really fun getting a more hands on class and I think there definitely should be more classes like this. I think they really help with understanding the content’. Hilary elaborated. ‘Since it was the last week of term it was a really relaxing and engaging way to learn about ciphers and codes. The way we re-created them was simple and easy, but still allowed us to think about the practicalities of each method. At first, I found the use of the Polybius square and Caesar cipher rather difficult and it took me a few tries to correctly do it, but after that I found it became quicker and easier to write the codes and figure out the massages of others. This was also made easier by the fact that certain letters appear again and again. The Scytale was really fun to make, though I didn’t initially realise how fiddly it would be writing the message onto the tube, I wonder if the Spartans had the same problem!’. Shiv, a postgraduate student, concurred. ‘I loved how it combined a hands-on approach to what we were learning about information technologies with an element of fun and interaction. By engaging in the exercises of writing with lemon and milk on paper, creating a Spartan Scytale, and encrypting messages with the Caesar Shift and Polybius Square, not only was I able to absorb the knowledge more efficiently, but I was also able to understand the physical dynamics of using such methods – the care / intricacy needed in the formulation of these messages, the time required, and many other factors’.
The next time I teach on the Ancient Technology in Context course, I shall definitely revisit this seminar. I might even start writing people messages in ancient code…
(If you would like to try and make a Spartan Scytale of your own, you will find instructions here, and there are plenty of videos of them in action available on YouTube)