Double Columnar Cipher Challenge

As one of my cybersecurity classes comes to an end, this will be my final blog. Most of my postings have covered Mac OS X security configurations or cryptology, both subjects being a great interest of mine. Other topics, such as National Cyber Security Awareness Month, just happened to coincide with the area I was studying. The Mac OS X source was myself, playing around with the features on my own Macbook. I incorporated other sources into the postings where applicable, and tried to use a variety.

I hope this blog will be useful to other students and security professionals by providing a clear understanding of the chosen topics and resources for more information.

Since the holidays are just around the corner, I thought I would put a little cheer in this finale. Not only will you learn how a double columnar cipher works, but I challenge you to crack my own code!

The first step is to pick two code words or phrases of the same length, and put each letter in its own column. Letter by letter, write out your message under the first code word/phrase, like this:

R	E	D	M	U	S	T	A	N	G
D	O	N	T	F	O	R	G	E	T
T	O	D	R	I	N	K	Y	O	U
R	O	V	A	L	T	I	N	E	R
A	L	P	H	I	E	X	X	X	X

In this example, the first code phrase is RED MUSTANG, and the message is DON’T FORGET TO DRINK YOUR OVALTINE RALPHIE. The message is not long enough to cover all the cells, so X’s are used for padding.

Next, order the code word/phrase according to the alphabet – 1 for A, and so on. If you have duplicate letters, I suggest numbering them in the order of appearance in the code word/phrase. It should look like this:

7	3	2	5	10	8	9	1	6	4
R	E	D	M	U	S	T	A	N	G
D	O	N	T	F	O	R	G	E	T
T	O	D	R	I	N	K	Y	O	U
R	O	V	A	L	T	I	N	E	R
A	L	P	H	I	E	X	X	X	X

Starting with the column under #1, string the message into blocks of 5 letters, continuing on to the next number if needed (do not count the code word/phrase, just the message). This makes the first ciphertext, which is GYNXN DVPOO OLTUR XTRAH EOEXD TRAON TERKI XFILI.

The first ciphertext is used to fill the cells under the next code word, NIGHT MOVES:

6	4	2	3	9	5	7	10	1	8
N	I	G	H	T	M	O	V	E	S
G	Y	N	X	N	D	V	P	O	O
O	L	T	U	R	X	T	R	A	H
E	O	E	X	D	T	R	A	O	N
T	E	R	K	I	X	F	I	L	I

To generate the final ciphertext, perform the same operation in the example above, with letters in blocks of 5: OAOLN TERXU XKYLO EDXTX GOETV TRFOH NINRD IPRAI. To decrypt, the operation is performed backwards, starting with this final ciphertext. If you know the code word/phrase, start by ordering the letters into numbers and place the first block of 5 letters into column #1, moving on to the next column. Once you have the cells filled in, do the same using the first code word/phrase.

Now that you have learned how to compose a double columnar cipher, I have two code phrases for you. The first is APPLE CIDER, and the second is SANTA CLAUS. The final ciphertext is NSAPO VHAAE AHFYA IEDHP YAANS ODSEL.

Happy Holidays!