# Classical Encryption Techniques 3

Transposition Cipher is an encryption method which elements are
rearranged.

There are many types of transposition cipher such as Rail Fence, Columnar Transposition and
Double Transposition.

Rail Fence is the simplest form of Transposition Cipher which the plaintext is written down as a sequence of diagonals and read off as a sequence of rows.

For Example:
The plaintext = `WELCOME TO CRYPTOGRAPHY`

Then the encryption algorithm will be

W L O E O R P O R P Y

E C M T C Y T G A H

So, the ciphertext = `WLOEORPORPYECMTCYTGAH`

We can make the encryption algorithm 3 rows

W C E C P G P

E O T R T R H

L M O Y O A Y

So, the Ciphertext = `WCECPGPEOTRTRHLMOYOAH`

In Columnar Transposition the plaintext is written down in rows and the
read off by the order of columns.

The order of columns is the secret key to Columnar Transposition algorithm, any spare spaces are filled with null or blank.

For Example:

The plaintext = `WELCOME TO CRYPTOGRAPHY`

The secret key = `615342`

Then the encryption algorithm

Now we read columns by it’s order (secret key)Note:I filled the spaces here with`ABC`

.

The ciphertext =

`ETTHMYACCCGAORRBLOOYWEPP`

previous types are easy to break because the ciphertext has the same letters frequency as the plaintext, and cryptanalysis can put the ciphertext in a matrix and playing with column positions.

Double Transposition is the same as Columnar Transposition but twice, this one is more secure.

For Example:
As the previous example

The plaintext = `WELCOME TO CRYPTOGRAPHY`

The secret key = `615342`

Then the encryption algorithm (first round)

The ciphertext = `ETTHMYACCCGAORRBLOOYWEPP`

And again

The plaintext = `ETTHMYACCCGAORRBLOOYWEPP`

The secret key = `615342`

Then the encryption algorithm (Second round)

The ciphertext = `TCRYYAOPHCBEMGLPTCRWEAOO`

Note:The ciphertext here has also the same letters frequency but playing with column positions now is harder.