Introduction to Transposition Techniques
Transposition technique is a cryptographic technique that converts the plain text to cipher text by performing permutations on the plain text i.e change the position of each character of plain text for each round. It includes various techniques like Rail Fence technique, Simple columnar transposition technique, simple columnar transposition technique with multiple rounds, Vernam cipher, and book Cipher to encrypt the plain text in a secure way.
Transposition Techniques
Below is the list of transposition techniques.
1. Rail-Fence Technique
Rail-Fence is the simple Transposition technique which involves writing plain text as a sequence of diagonals and then reading it row by row to produce the cipher text.
Algorithm
Step 1: Write down all the characters of plain text message in a sequence of diagnosis.
Step 2: Read the plain text written in step 1 as a sequence of rows.
To understand it in a better manner, let’s take an example.
Example: Suppose plain text corporate bridge and we want to create the cipher text of the given.
First, we arrange the plain text in a sequence of diagnosis as shown below.
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Now read the plain text by row wise i.e. croaerdeoprtbig.
So, here the plain text is corporate bridge and cipher text is croaerdeoprtbig.
The Rail-Fence technique is quite easy to break.
2. Simple columnar transposition techniques
The simple columnar transposition technique can be categorized into two parts – Basic technique and multiple rounds.
Simples columnar transposition technique – basic technique. The simple columnar transposition technique simply arranges the plain text in a sequence of rows of a rectangle and reads it in a columnar manner.
How does this algorithm work?
Step 1: Write all the characters of plain text message row by row in a rectangle of predefined size.
Step 2: Read the message in a columnar manner i.e. column by column.
Note: For reading the message, it needs not to be in the order of columns. It can by any random sequence.
Step 3: The resultant message is cipher text.
Example: Let’s assume that Plain text is a corporate bridge and we need to calculate the cipher text using a simple columnar transposition technique.
Let’s take 6 columns and arrange the plain text in a row-wise manner.
| Column 1 | Column 2 | Column 3 | Column 4 | Column 5 | Column 6 |
| c | o | r | p | o | r |
| a | t | e | b | r | i |
| d | g | e |
Decide the column order for reading the message – let’s assume 1,3,5,2,4,6 is an order.
Now read the message in a columnar manner using the decided order. – cadreeorotgpbri
cadreeorotgpbri is a cipher text.
3. Simple columnar transposition technique – Multiple rounds
Simple columnar transposition technique with multiple rounds is the same as basic only the difference is, in multiple rounds, we iterate the process multiple times.
Working of an algorithm
Step 1: Write all the characters of plain text message row by row in a rectangle of predefined size.
Step 2: Read the message in a columnar manner i.e. column by column.
Note: For reading the message, it needs not to be in the order of columns. It can by any random sequence.
Step 3: The resultant message is ciphertext.
Step 4: Repeat the procedure from step 1 to step 3 many times as desired.
Example: Let’s assume that Plain text is a corporate bridge and we need to calculate the cipher text using a simple columnar transposition technique.
Let’s take 6 columns and arrange the plain text by row-wise manner.
| Column 1 | Column 2 | Column 3 | Column 4 | Column 5 | Column 6 |
| c | o | r | p | o | r |
| a | t | e | b | r | i |
| d | g | e |
Decide the column order for reading the message – let’s assume 1,3,5,2,4,6 is an order.
Now read the message in a columnar manner using the decided order. – cadreeorotgpbri
cadreeorotgpbri is a cipher text.
Let’s perform step 1 to step 3 one more time.
| Column 1 | Column 2 | Column 3 | Column 4 | Column 5 | Column 6 |
| c | a | d | r | e | e |
| o | r | o | t | g | p |
| b | r | i |
In the second iteration, the order of the columns will be the same.
Cipher text – cobdoiegarrrtep
Continue the same procedure if more iteration is required.
4. Vernam Cipher
A subset of Vernam cipher is called a one-time pad because it is implemented using a random set of nonrepeating characters as an input cipher text.
Note: Once the input cipher text is used for transposition, it never used for any other message. The length of input ciphertext must be equal to the length of plain text.
Working of Algorithm
Step 1: Arrange all characters in the plain text as a number i.e. A = 0, B = 1, ….. Z = 25.
Step 2: Repeat the same procedure for all characters of the input ciphertext.
Step 3: Add each number corresponding to the plain text characters to the corresponding input cipher text character number.
Step 4: If the sum of the number is greater than 25, subtract 26 from it.
Step 5: Translate each number of the sum into the corresponding characters.
Step 6: The output of step 5 will be a cipher text.
In Vernam cipher, once the input cipher text is used, it will never be used for any other message, hence it is suitable only for short messages.
Example: The plain text is educba and cipher text is ntcbar
| Plain text | e | d | u | c | b | a |
| 4 | 3 | 20 | 2 | 1 | 0 | |
| Input cipher text | n | t | c | b | a | r |
| 13 | 19 | 2 | 1 | 0 | 17 | |
| Addition of plain text and input cipher text | 17 | 22 | 22 | 3 | 1 | 17 |
| Cipher text | r | w | w | d | b | r |
Hence, cipher text is rwwdbr.
Recommended Articles
This is a guide to Transposition Techniques. Here we discuss the basic concept and List of Transposition Techniques with steps, examples, and working of Algorithms. You may also look at the following article –
