An RSA cryptosystem has public key N 35 and e 7. Messages are encrypted one letter at a time, converting letters to numbers by A 2, B 3, . . . , Z 27, space-28. (a) Showing your work, encrypt the message BE GOOD. (b) Find the decryption exponent d and decrypt the message 20 23 26 7 15 16 (c) This choice of N and e has several weaknesses. Name at least two different ones. (d) Even if a good choice of N and e is made, the method of encrypting one letter at a time has weaknesses. Describe how we might find the plaintext if a very long ciphertext is given. An RSA cryptosystem has public key N 35 and e 7. Messages are encrypted one letter at a time, converting letters to numbers by A 2, B 3, . . . , Z 27, space-28. (a) Showing your work, encrypt the message BE GOOD. (b) Find the decryption exponent d and decrypt the message 20 23 26 7 15 16 (c) This choice of N and e has several weaknesses. Name at least two different ones. (d) Even if a good choice of N and e is made, the method of encrypting one letter at a time has weaknesses. Describe how we might find the plaintext if a very long ciphertext is given