Classic Cryptography

Contents

Contents

Contents

Introduction to Transposition Ciphers

What is Transposition?

Transposition is the act of rearranging objects.

We could rearrange the letters in a word to create an anagram, this is an example of letter transposition.

What is a transposition cipher?

To make the transposition of letters a cipher, it has to be done to a regular system or pattern known to both the sender and receiver of the message.

We have included a range of different transposition ciphers, their rules, examples, and exercises.

Scytale Ciphers

This is an ancient cipher technique recorded as being used by the Military of Greece and Sparta

It involved wrapping a strap of leather around a rod of a set thickness/number of sides to encrypt and decrypt messages on it

So if you needed to write the message 'We are surrounded Send reinforcements fast' using a four sided scytale (this is what the rod was called), you would wrap the leather around the scytale and write the message along each of the scytale's sides.

The Rail Fence Cipher

This is also referred to as a zig-zag cipher and is an evolution of scytale cipher.

Instead of writing the message along horizontal lines, it zig-zags up and down several lines. The number of lines is the key to the ciipher that only the sender and receiver would know.

For example, let us start with the message 'The target is on the move Please advise action'.

We shall use 3 lines for the zig-zag and start the message in the top left.

The below shows how this would appear. For anyone using a screen reader, we have used tables to show the placement of letters.

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The encrypted message is then created by re-writing the message as it reads left to right on each line.

In this case: Tatnm Psvao htrei oteoe laedi ecine gshve ast

The challenge with this cipher, is that the decryption process is time consuming. The best approach is to draw a grid which has the same number of lines as the key says, and a column for each letter of the message.

Let's decrypt the following message: Heaep odctr fnihw orpal ccety ier

This uses a key of 4 lines and there are a total of 28 letters.

This means we need a table made up of 4 rows and 28 columns.

The starting point is the top left square. From there, mark each box on the zig-zag path, as shown below.

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Now, replace each of these marked boxes with the coded message, from left to right on each rown in turn.

So, the first row will look like this:

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Once all the letters have been added, follow the zig-zag to read the message.

Reveal Answer

Route Ciphers

Coming Soon

Columnar Transposition

Coming Soon

Myszkowski Transposition

Coming Soon

Transposition Exercises

Coming Soon

The completed grid:

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The decrypted message: How to decrypt a rail fence cipher.