Decrypt the message “WTAAD” using the Caesar Cipher with key=15

Solution: To decrypt the Caesar-cipher text WTAAD with key = 15, shift each letter backward by 15 positions in the alphabet.

• W → H (W = 22; 22 − 15 = 7 → H)

• T → E (T = 19; 19 − 15 = 4 → E)

• A → L (A = 0; 0 − 15 = −15; add 26 → 11 → L)

• A → L (same as previous letter)

• D → O (D = 3; 3 − 15 = −12; add 26 → 14 → O)

Decrypted message: HELLO