The secret key can be made by filling the first and part of the second row of a matrix with the word MORNING. Filling of rest of the matrix can be done using remaining alphabets. Consider alphabets Y and Z together in one cell of matrix. -

i. Secret Key = MORNING

ii. Plaintext = attack cancelled on Monday wait for next message

iii. Considering Y and Z in one cell matrix

iv. The playfair cipher matrix is as follows:

v. Dividing the plain text into blocks:

at ta ck ca nc el le do nm on da yw ai tf or ne xt me sx sa ge (x is added because similar letters cannot be paired)

vi. Using the following rules we form the cipher text-

1. If both letters are in the same column, take the letter below each one (going back to the top if at the bottom)
2. If both letters are in the same row, take the letter to the right of each one (going back to the left if at the farthest right)
3. If neither of the preceding two rules are true, form a rectangle with the two letters and take the letters on the horizontal opposite corner of the rectangle.

Ciphertext: DP PD DJ DB CJ LU UL AI IO RI GB ZX DO PK RN MJ YS GL XN PC EL