Question

Using playfair cipher, decrypt the ciphertext “GKSKHALTYZ” using the keyword “UNIVERSITY”

Answer 1

The playfair square formed using the keyword "UNIVERSITY" is:

Algorithm to decrypt the ciphertext: The ciphertext is split into pairs of two letters (digraphs). The ciphertext will always have even number of characters.

Rules for Decryption:

1) Both the letters are in the same column: Take the letter above each one (going back to the bottom if at the top).

2)Both the letters are in the same row: Take the letter to the left of each one (going back to the rightmost if at the leftmost position).

3) Neither of the above rules is true: Form a rectangle with the two letters and take the letters on the horizontal opposite corner of the rectangle.

The ciphertext GKSKHALTYZ is broken down as : GK SK HA LT YZ

For the first pair, se see that in the square, The letter G and K are in different rows and columns, so Rule 3 is applied and we get CO as the result

For the second pair, SK, in the square we see that they are in the same column therefore Rule 1 is applied and we get NC as the decrypted text.

Similarly, applying the same procedure for all the pairs, we get the result:

Answer : CONCORDIAX