I have understood the "equivalences" between PRP, PRF and PRG. Now, I just read an statement in my lecture notes that made me think that there has to be a conversion between PRG and computationally secret encryption scheme:
So, our definition of PRG is sufficient for the existence of a computationally secret encryption scheme. Later, we will see that this is definition is the right one as PRGs exist if computationally secret encryption schemes exist.
This means I can build a PRG from a computationally secret encryption scheme. What is the common and easy way to see this?