Secret Codes #11
Secret codes embedded in music? Image steganography? John has a long moustache? Indigenous Americans who served as code talkers in World War 2? The world of secret codes and ciphers is HUGE and we can't cover it all!
For our last puzzle, let's try another transposition cipher, in the same family as the rail fence cipher (Secret Codes #7). Remember, this is a fancy way of scrambling the letters, not substituting them for something else. This one is called "columnar transposition".
Let's start with an example of how to encrypt a message. (See if you can figure out how decryption works by working backwards from this example.)
- Start with a key. For this example, we'll use "ANSWER" written here in lavender spaces. Each letter in the key will be at the head of its own column.
- The plaintext is "THE CHAIR IS AGAINST THE WALL" written in orange spaces.
- Write the plaintext left to right across filling the columns. The plaintext happens to be a multiple of 6 letters so there are no blank spaces. If there were, you could fill them in with any letter.
- Number the columns according to the alphabetical order of the letters in the key. Column order has a green background here.
- Write the ciphertext (not the key) in column order: "TIAH HATL HRIE AGTL EINW CSSA"
If you are having trouble deciphering the message:
- Start by numbering the blocks of text. TIAH = 1, HATL = 2, HRIE = 3, etc.
- Write the key and label its letters in alphabetical order. ANSWER = 1 3 5 6 2 4
- Write the blocks of text as columns in the order of the key. So the first column will be block 1 (TIAH), the second column will be block 3 (HRIE), etc.
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I used a spreadsheet to layout the cypher.