Transposition Ciphers

The Basics

Transposition ciphers, where the letters are moved around, are something that most people have a bit of experience with. Anagrams are possibly the most simple of these ciphers. In an anagram the letters within a given word are rearranged.

ATLANTIA = NATALIAT

This is a basic example where I've just scrambled up the letters. Order can be applied in any number of ways. For example you can move all of the vowels a certain number of spaces forward or backward. To introduce additional complexity more complex messages can be mixed using the message length rather than the word length. Below is an example of a 'rail fence' pattern (Smith, 1955).

ATLANTIA IS THE BEST
Becomes....
A L N I  I  T E  E T
 T A T A  S  H  B S
Which becomes....
ALNIITEET TATASHBS

Geometric patterns can be used in a variety of interesting way. This is fundamentally the same operation that is performed by the Skytale. Consider some of these other patterns. Note: I use the letter X here for simplicity but padding letters should not be uncommon letters like X or Z. Use something like a progression of vowels to screw with any cryptanalysis. What's the point of being evil if you're not going in whole hog? :-P

ATLANTIA IS THE BEST
  5x4 grid, vertical, with padding.
ANIET
TTSBX
LITEX
AAHSX

ANIET TTSBX LITEX AAHSX

Khan describes numerous variation on this theme. For example, using the same 5x4 grid above you can develop your transpositions by interlacing the rows 1,3,2,4 (ANIET LITEX TTSBX AAHSX). Other options include perimeter progressions like clock wise, starting from the lower left (ALTA NIET XXXS HSIT SBET), and so on.

Devices and physical examples

The Scytale ('skittle') is, without a doubt, the most commonly referenced example a a transposition cipher in use. The basic idea of the scytale is that by wrapping a strip of cloth, leather, etc, around a rod of a specific diameter you define a physical spiral that acts as the 'key' for deciphering the message. For example: Apprentice to Belphoebe Vivant Atlantia, when wrapped around the right size of rod would appear as such....

_____________________________________________________________
       |   |   |   |   |   |   |   |   |   |   |   |   |
       | a | p | p | r | e | n | t | i | c | e |   |   |
     __| t | o | b | e | l | p | h | o | e | b | e |___|
    |  | v | i | v | a | n | t | a | t | l | a | n |
    |  | t | i | a | ! |   |   |   |   |   |   |   |
    |  |   |   |   |   |   |   |   |   |   |   |   |
_____________________________________________________________

When unwound the letters would read from top to bottom as

_____________________________________________________________

atvtpoiipbvarea!eln npt tha iot cel eba  eb
_____________________________________________________________

Here is an example done on a leather belt. To avoid making it overly busy, remembering that the goal is to share information in this context rather than to obfuscate it, I've just used the word 'apprentice'.

Here is what the belt looks like when looked at normally.

Here is the 'deciphered' message (1" rod).

Finally, here is an impropperly deciphered message (1.5" rod)

Here is another example with a bit more 'going on', to show how effective this method can be at hiding information. (also seen on this page over here)

Here we have the 1" rod and a simple ribbon.

Here is the ribbon on the staff. I used tape but anything would work. A tack, a rock, a split in the wood. Whatever.

Now I add a basic message. w00t Atlantia!

Here I've unwound the ribbon. Kinda hard to see what's there, isn't it?

Rewrapping. Notice that even wrapping it differently can make the message unreadable.

Wizardry!

Now I've wrapped the same ribbon on a slightly larger staff (maybe a 1/4" difference) and the message is illegible.



Just a pile of ribbon, or a declaration of allegiance? BOTH!