If we received a ciphertext message in Jefferson cipher, the first thing we would need to do is to split the message into 36 columns so that each encoded line also has its own line in the table, as shown below.

With the message in the table, we can now try to find polygraphs that repeat themselves in the different rows. The premise behind finding these is that hopefully the encoder may have encoded a combination of letters more than once, and possibly each time he chose to use the same ciphertext row. If that happened, the ciphertext would be equivilent in another row.

Of course, we can't just find one digraph in two rows and assume that we're done. But, since we're dealing with just 36 letters, the chances of even a few polygraphs is fairly small. We can use the expected number of digraphs, trigraphs etc… table to help let us know when we should get excited or not worry about it.

Now, once you do find a row that is matched to another row, you can be sure that the columns for each of those all represent the same cipheralphabet. Each of the columns within these rows can be attacked as monoalphabetic substituion.

But, with a short message, that would mean that you probably don't have much to go on for a solution…possibly only a letter or two. This brings into play the probable word method. And while testing words will be a tedious process, it eventually works.

When you attempt different words, you should remember that no ciphertext letter can represent the same plaintext letter. If you find ciphertext 'e', it can't represent plaintext 'e'. Furthermore, if you've concluded that some rows are from the same cipheralphabet, you can eliminate possibilities when you read over them.

The Jefferson cipher is a very difficult cipher system to break, and has confused many professional cryptanalyists even in the 20th century. It's simplicity and power are perhaps unmatched in the world of cryptography even today. And to think that it was created by a man who probably had little idea of previous cryptanalysis.

Are you ready to test your knowledge about Jefferson? That's right. This CryptAgent challenge is a little different than most others. Click here for the Jefferson CryptAgent Challenge!! If you're not a CryptAgent, you can find out more and register if you like. It's free, and it's fun!