For example, using the ASCII values of characters, the message THE_EAGLE_HAS_LANDED can be encrypted using E and PQ to THJZJAGQJZHAXZQANIJI. This can be decrypted back to the original message only by someone who knows D and PQ. To find your private key D, a hacker needs to factor PQ into P and Q and there are no known methods to do this in a realistic amount of time if PQ is large!
Prof. Ashay Dharwadker