In the second round, the permuted order of the column is 2, 3, 1, 4. Now, again we have to put the cipher text of round 1 in the rectangle of size 3×4 row by row and permute the order of columns before reading the cipher text for round 2. Now after the first round the cipher text obtained is as follow: Proceeding with the next step, the order of the columns of the matrix is permuted as you can see in the image below: Let us put this plain text in the rectangle of predefined size of 3×4. We will consider the same example of a basic columnar technique which will help in understanding the complexity of the method: Let us discuss one example of a columnar transposition technique for better understanding. Step 3: To obtain the final cipher text repeat the steps above multiple time. Before reading the text in rectangle column by column, permute the order of columns the same as in basic columnar technique. Step 2: To obtain the cipher text, read the plain text in the rectangle, column by column. Step 1: The plain text is written in the rectangle of predetermined size row by row. The steps for columnar technique with multiple rounds are as follow: The basic columnar technique is performed over the plain text but more than once. It is similar to the basic columnar technique but is introduced with an improvement. So, a more sophisticated technique was required to strengthen the encryption.Ĭolumnar Transposition Technique with Multiple Rounds The cryptanalyst only has to try few permutation and combination over the order of column to obtain the permuted order of column and the get the original message. Similar to the rail fence cipher, the columnar cipher can be easily broken. So, the cipher text obtained by the columnar transposition technique in this example is: Now, to obtain the cipher text we have to read the plain text column by column as the sequence of permuted column order. And we have also permuted the order of the column. As you can see in the image below the plain text is placed in the rectangle of 3×4. For our example, the predefined size of the rectangle would be 3×4. Now, put the plain text in the rectangle of a predefined size. To understand the columnar transposition let us take an example: The obtained message is the cipher text message. But you have to permute the order of column before reading it column by column. Step 2: To obtain the cipher text read the text written in a rectangular matrix column by column. Step 1: The plain text is written in the rectangular matrix of the initially defined size in a row by row pattern. The steps to obtain cipher text using this technique are as follow: The columnar transposition cipher is more complex as compared to the rail fence. So, there was a need for a more complex technique. Rail fence cipher is easy to implement and even easy for a cryptanalyst to break this technique. Now, to obtain the complete cipher text combine both the halves of cipher text and the complete cipher text will be: Reading the second row of the rail fence, we will get the second half of the cipher text: So, reading the first row the first half of cipher text will be: Once you have written the message as a sequence of diagonals, to obtain the cipher text out of it you have to read it as a sequence of rows. Looking at the image, you would get it why it got named rail fence because it appears like the rail fence. Now, we will write this plain text sequence wise in a diagonal form as you can see below:
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