I encourage you to use Latex, but even if you don't, please type your answers or hand write nicely. Explain your argument in a brief and precise way.

1. In a symmetric cryptosystem, Alice and Bob both know the e-key and the d-key. The cryptosystem is assumed to have no weakness and Alice and Bob are the only persons that ever know the secret keys. Alice sends some message m to Bob. Is it possible for Bob to prove to a judge that he really has received m from Alice (in other words, does a symmetric cryptosystem offer non-repudiation)? Say YES or NO and give a short and clear explanation.

2. ciphertext was produced with an affine cipher. Decrypt it and explain how you did it. There are a number of software tools available on the web (for example to count the frequency of letters, to do modular arithmetic, etc.) You can use such tools but not one that automatically provides the plaintext. You can also write a short program that does brute-force search. In case you use internet tools, you need to say what tool you have used and still explain what steps you did. In case you write your own program, include the code (which should have sufficient comments).