Exercise 4 (2 pts). In the Elgamal cryptosystem, Bob's public key is (p 23.g 7,g 4) His private key is= 6 Alice uses Bob's public key to encrypt a message M for him. The resulting ciphertext is (d = 11. k = 21). Recover the message M. (You can use online modular cakculators available at the Web.)