These are my answers for Tutorial 4 (Wednesday November 9). I suggest that you spend some considerable time trying to solve the questions yourself before looking at those solutions.
Btw... I think that I got the number correctly (tutorial 4 was on Wednesday the 9th), right?! If not, just post here and let me know.
And speaking about that, we could easily use this page to exchange info. If you have any questions related to the course, feel free to ask!
Download Tutorial 4 solutions
No problem, hope that helps..
ReplyDeleteBtw, I think the question with RSA is a little bit unrealistic. I think it's going to be a good practice to try an example of your own! Pick 2 small primes (i.e. 7, 13), compute their product n, find \Phi(n), etc, etc..
The only tricky part would be to raise to some big power modulo n. In real life, people would use the method of repeated squares (also works perfectly for your examples). In your case, if x happens to be coprime with n, you can also use Euler's theorem. See this, for instance, on reducing large power modulo n:
http://en.wikipedia.org/wiki/Euler's_theorem
In real life, numbers would be huge and nobody would be able to find Φ(n) except the one with the secret keys, but who cares about real life when you have a test :)