The talk on Tuesday be Dimitris Papadopoulos will be on  
Factoring and Primality testing.  It would be very helpful 
to go over some basic group theory and number theory.

You can find this material at the 2 links below. 

https://www.math.lsu.edu/~adkins/m4201/cyclicgroup.pdf [www.math.lsu.edu]
http://math.mit.edu/~mbehrens/18.904/groups.pdf [math.mit.edu]