12. Polybius Square

In this episode, we talking about Polybius Square with Dangerous Dave and Dan. Polybius Square can be used in many ways and is basically an ancient form of Morse Code, but less developed.  We also talk about ADFGVX cipher, ask the characters about their favorite episodes, and hear the concluding story!

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This is the final episode of the season. Thank you for listening. Without listeners, we wouldn't be making this show.

The background music from this episode Bio Unit, Conduit, Travel, Energy Drink, Apex, Maze, Mainframe, Generator, and Moving Sun, all by Bio Unit, and our theme music is Mosquito by Caspar Babypants.

 You can find Dr. Gareth's work at drgarethmoore.com. He has released many puzzle and cipher related books for kids, as well as a lot of stuff for adults, too. 

Thank you for listening.

Transcript

Barnabas  01:02
Welcome back. This episode features grid codes, World War I, Terrible jokes, unbrainwashng, and clumsy crime. Without further ado, start the show.

Barnabas  01:59
It's the final episode of season 2, and we're talking with Dangerous Dave and Dan about Polybius Square, also known as Polybius Checkerboard and Greek Square Cipher. I'm Barnabas, and with me is Steve. Dangerous Dave, it's your turn for the key.

Dangerous Dave  02:25
Polybius Square is simple. Draw a 5x5 grid and put all the letters in the alphabet. Because there are 26 letters in the alphabet and the grid can only hold 25, 2 letters have to share the same square. This is usually I and J, but X and Y, Y and Z, or C and K work as well. To find a letter you want to use to send a message, find that letter on the grid and put the number of it's column and then it's row on the grid. That is the standard way. Sometimes, though, you can put the row first, so that 24 would be 42. There are 2 ways of adding numbers. The first way is to change the grid from a 5x5 to a 6x6. Then in the extra squares write the numbers 0 to 9 and separate the letters into single boxes. The other possibility is to make the numbers share boxes with early consonants in the alphabet. B would be 1, C 2, D 3, F 4, G 5, H 6, K 7, L 8, M 9, and N 0.

Dan  04:39
There's a variant taken from this called Playfair, or Keyed, Cipher. Keyed Cipher is basically just where you have a word that you use and you put the letters in that word in the first few boxes of the grid. That is the plain keyed version. Playfair is keyed. The key, in this case, is PLAYFAIR, but there are several extra rules. 1. If a pair of letters appear on the same row of the table, replace them with the letters to their immediate right, respectively. If it's on the right of the row, wrap around to the one on the left side. If the letters of a pair appear in the same column of the table replace them with the letters immediately below, respectively, and the same from the other thing about wrapping around works here too. If the letters of the pair are not in the same row or column, replace them with the letters in the same row of the letter of the letter and on the column of the other letter in a pair. But for you to understand that, first you need to know that the message is immediately split into groups of 2. There is also occasionally Xs added to the word as nulls. So, in this case, HELLO WORLD as a message becomes KG YV RV VQ GR CZ. Then they're encrypted with the Polybius square method.

Barnabas  07:08
Thanks for that. Here's another cool variant of Polybius square - the ADFGVX cipher. Say that three times fast.

Dan  07:25
That, that, that.

Barnabas  07:27
The ADFGVX cipher was first called ADFGX before they added a V. There are six possible letters in ADFGVX cipher - A, D, F, G, V, and X. Instead of numbers on the square, like in the Polybius square, those letters are used. The alphabet is usually mixed up as well. The message was encoded with a pair of letters and then put in rows under a keyword. Then the keyword is mixed around so that the letters [of the keyword] were in alphabetical order and then read off in columns. The ADFGVX cipher, unlike the ADFGX cipher, has added digits 0 through 9.

Announcer  08:41
And now it's time for Steve's Tips.

Steve  08:52
Hi everybody, this is Steve, and I'm here for Polybius Square. There are a lot of different things used in Polybius Square and Polybius Square is also well known, so try to mix up the letters a lot to make it harder for the enemy to understand. Also, mix up the numbers on the outer part of the grid. A good way to do this is to use a keyword, so try that. Because Polybius is relatively insecure, it might be a good idea to do a chain with other codes or use ADFGVX cipher or Playfair cipher. That's all we have today on Steve's tips. Now, back to Barnabas.

Barnabas  10:02
Thanks for that, Steve. Polybius Square has a very interesting history. So does Polybius [himself]. Polybius was a Greek historian and Scholar - a famous one, too - and he wrote down a book of histories in which he promoted Polybius Square, which has come to be known that because of him, but he was not the creator. Polybius Square was actually created by the ancient Greeks  Cleoxenus and Democleitus (I hope I'm saying that right) created the basic parts to it. Polybius, however, made it more complete. In his histories, Polybius talked about the need for effective signaling in warfare, leading to the development of the square. Previously, fire signaling was useful for expected and predetermined messages, with no way to convey new messages about unexpected events. According to Polybius, Aeneas Tacticus devised a water using semaphore system consisting of matching pots and such with rods labeled with different messages, such as "heavy infantry", "ships", or "wheat". This system was slightly better than the basic fire signaling, but it still did not have the ability to convey any new messages. The Polybius square was used to aid fire signaling. To send a message the sender would initially hold up two torches and would wait for the other person to signal with the other set that they were ready to receive the message. The sender would then hold up the first set of torches in his left