Coded Messages: Sending Messages

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What is one of the most important skills to have as a spy? Being able to send secret messages to your partner in espionage, of course! Whether that message is on paper, in a dead drop, or sent over a questionable connection, it must be encrypted. Unfortunately, most high strength ciphers require either a computer of some sort, or hours upon hours of time spent using pen and paper for a relatively short and simple message. Good news! There are a few ciphers (or codes) that are nearly impossible to break with only pen and paper, and at the same time, they have some resistance to computers.

These awesome ciphers are the Vigenére cipher and the ADFGVX cipher. The Vigenère cipher is a system of encrypting alphabetic text by using a series of interwoven Caesar ciphers. A Caesar cipher ( pic 2) basically takes a plaintext letter, in this case A, and changes it to a ciphertext letter, in this case C. A to C is a shift of 2. A shift of 1 would turn A into B. Alone, Caesar ciphers are fairly weak. ADFGVX is a fractionating transposition cipher which combines a modified Polybius square with a single columnar transposition.

Check out the second half of my Coded Messages Series! Coded Messages: Cracking Messages

Image by Pete Linforth from Pixabay

• Pen
• Pencil
• Paper

Image by tigerlily713 from Pixabay

The Vigenére cipher was first conceived by Italian Giovan Battista Bellaso in 1553. The Vigenére cipher was not broken until 1863. This earned it the description of le chiffrage indéchiffrable (French for 'the indecipherable cipher').Many cryptologists have tried to implement different ciphers that have their roots in the Vigenère cipher. In 1863, Friedrich Kasiski was the first to publish a general method of deciphering Vigenère ciphers.

In the 19th century the Vigenére cipher was mistakenly credited to Blaise de Vigenére (1523–1596) and so acquired its present name.

First, write out your message in normal print. This is called the plaintext. Next, write out your keyword (in this case the keyword is IBLES) above or below your plain-text. Make sure your plaintext letters and your keyword letters match. I placed the key above the plaintext in my example. After this has been done, pull out your Tabula Recta (or Vigenére Square) and use it like a grid. Since "I" is the first letter of the keyword, it will be used first. The corresponding letter of the plaintext, in this example, is "S". Go to the top of the Vigenére Square and find "S" follow the "S" column down until you get to the "I" column. Where the two columns intersect there will be a single letter. The is the first letter of our ciphertext. Repeat this process until all of the plaintext and key letters have been changed into ciphertext letters.

To make the ciphertext (or output of the Vigenére Square) more secure against computers and pen and paper code-breakers, misspell the plaintext. For instance, instead of saying "There is something suspicious about Bob," instead say "TTh ere iss sumthxng suzpicius abouBo b." This will make it more difficult for computers to crack the cipher and for pen and pencil operations, it will be very confusing.

An additional layer of security can be added to the cipher by using a running key. The normal type of key is a single word (or series of words in some cases---the words stay in the same order). A running key is a key that does not repeat itself. Because the key does not repeat itself, the amount of letter change between plaintext and ciphertext is constantly being altered. One example of a running key would be this: Thisisanexampleofarunningkeythewordsdonotrepeatthemselves and on and on... This makes the cipher much harder to crack.

Image by Pete Linforth from Pixabay

ADFGVX was a military cipher used by the Germans in World War 1. ADFGX was invented by the German signal corps officer Lieutenant Fritz Nebel and was introduced in March 1918. It wasn't until June 1918 that ADFGX was modified with an extra layer of security by adding the V to make it AFDGVX. In addition to the extra security, adding the V made it a six by six grid instead of a five by five. Having a larger grid means that numbers can be included in the encryption. Since this was originally a military cipher, numbers were often transmitted. Before the update, numbers were spelled out letter-by-tedious-letter.

ADFGVX is somewhat similar to Vigenére in terms of using a encoding device (piece of paper with numbers, symbols, letters, etc.) to turn plain-text into ciphertext. To encode messages with ADFGVX, write out the plain-text. After the plaintext has been written, use the encryption block (pic 1) to find the first letter of the plaintext. In my case, the letter is an "S." Below the "S" I wrote an "FA." The "FA" is my first section of ciphertext. Always remember to write the two ciphertext letter in the same order (left letter first, then the top letter). For the next letter "I" the ciphertext will be "GV." Repeat this process until all of the plaintext has been encoded.

Now that we have the ciphertext, we will add a second layer of encryption. To do this, choose a keyword. For my illustration, I chose Autodesk. Write your keyword at the top of your paper(make sure there is plenty of space between letters). Under each letter of your keyword, write one letter of your ciphertext. Once you have reached the end of your keyword, simply start a new row below you first line of ciphertext. It is very important to keep all columns lined up with one another. If you use up all of your ciphertext, but still have a few letters of your keyword, fill in the remaining spaces with X's. Finally, for the last layer of encryption, we will arrange the keyword alphabetically. In my illustration, that turns Autodesk into Adekostu. All the letters in the "A" column (F, G, F, V) will stay in their order under the A. Do not for any reason change the order of the letters under "A." Since the keyword has been reordered alphabetically, "A" column remains the first column. Instead of the next column being "U" it is now "D." All the letters in "D" column will stay in their same order under "D" (the only change is from being the second letter of the keyword to being the fifth letter). Repeat this process until all letters and columns of the keyword have been reordered.

Once the message has been received, it needs to be read.

To decrypt a Vigenére cipher, simply find the first letter of the key in the Tabula Recta and follow its row or column until you come to a letter matching the corresponding ciphertext letter. In my illustration, the first letter of my key is "I" and the first letter of my ciphertext is "A." So, I follow the "I" column until I come to an A. After I find the "A" I trace it up to the top of the Tabula Recta until I find the last row. Whichever letter I land on is the first letter of the ciphertext. (Refer to picture 2)

To decrypt an ADFGVX cipher, begin by changing the keyword (currently Adekostu) to its original form(Autodesk). Follow the same column rules. For instance, the "D" column and all of the letters under it should stay in the same order--- the only change should be the position of the "D" column (and all of the letters in it) in relation to the keyword. Next, go back to the encoding device and find the first two letters (in my illustration the first two letters are "F" and "A"). Trace the two letters down their respective row or column until the row and column meet. At that meeting point, there will be a single letter. That letter is the first letter of the plaintext. Repeat this process until all of the ciphertext has been turned into plaintext.

Congratulations! You are now an amateur cryptographer!

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