Transposition cipher is a cipher in which the characters of the plaintext are changed without any change in their identity. That is, this cipher changes the arrangement of the characteristics of plaintext to get the ciohertext.
Let’s see an example of transposition cipher:
Suppose we have this sentence: THE ENEMY IS CLOSE. So, this could be written in the following pattern:
1 2 3
T E M S O H N Y C S E E I L E
And this could be encrypted along the “route” as specified in the key. If the order in the key is to follow along the top-left side to down right-side then the ciphertext would be TEM SOHNY CS EEILE. These secure routes would often leak away important parts of the message thereby breaking the encryption. Hence, it was not widely used or used with another cipher.
Just like how substitution ciphers can be broken with the help of frequency analysis of each letter in the ciphertext similarly transposition ciphers can be broken too! This is done with the help of similar method of frequency analysis of the adjacent letters of plaintext which may help to identify the algorithm that has been used to do the transposition.