With just a ruler and a little math, it's easy to determine the diameter of the cylinder used to encode a skytale message. For example, let's say that we found a message created with the skytale system. To determine the diameter of the cylinder, all we have to do is to find the circumerfence. And, to find the circumference, we just need to measure the distance between two letters which are aligned next to one another when wrapped around the cylinder. In our message, we had the following…

Quick graphical example

When looking that the message, it's clear that there were four lines of message written, with one letter written per each width of the strip. Now, if we measure the distance between the first letter of the first set of letters and the first letter of the second set of letters, we will have the circumference of the circle. Remember that these letters line up when wrapped around the cylinder, which means that the length of paper between them must be the circumference.

Once we have a number, we simply use the circumference of a circle formula to find the radius.

Circumference = 2*pi*radius

So, we divide our circumference by 2*Pi, or about 6.28. The resulting number is the radius of the cylinder used to encode/decode this particular message. The next step is of course to find a cylinder which fits this description.

Of course, you can always just cut the skytale message into separate pieces and then play with them until they line up…which isn't too hard to do. BUT, if you're planning on not letting the enemy know that his cipher was intercepted and planned on sending it on the recipient, cutting the message isn't a good way to maintain secrecy.

CryptAgent Challenge time again! This one is going to require you get up from your computer and actually do a little hands on work. As you might have guessed...you have to make a skytale system! If you're not a CryptAgent, you can find out more and register if you like. It's free, and it's fun!