The Clues
All the information you might need is here in the post
UmVtZW1iZXIgdGhhdCBhdCBmaXJzdCB5b3UgYXJlIG9mZiBieSBvbmUu
DRMExcuKJrKSGE/1gra4JJQ2k7btp2od2nJNTPNfYEuoCC53urhzAHPwXZ/Lh4vzqaNLFvfLJvaaTj0jesNxng==
(All the information you need can be seen in the above section. You do not need to look anywhere else for clues.)
What is this?
This puzzle is a sort of "puzzle-ception," inspired by Cicada 3301. Once you solve the puzzle in the clue section, you will find another puzzle. Upon solving that, you will find another puzzle, and so on.
If no one is able to progress in a day, I will post a hint in the hint section below. Once someone solves a layer, I will also add it to the hint section.
Collaboration is Key!
This puzzle is fairly difficult, and will probably take several days minimum for the community to solve. I highly recommend that you collaborate, and if you make a breakthrough, post as an answer!
Hints/Solutions
2 hints for the first phase.
Hint #1: AES-128bit. The key is 32 hex characters long (16 ASCII characters).
Hint #2: The key is in "The Clues" section. It is almost literally told to you.
0 hints for the second phase.
0 hints for the third phase.
The question has been solved! I am working on a much more elaborate puzzle in the same style of this, which I will try to release in a couple of days.
Edit
It turns out that I was using a faulty algorithm for the AES-128 encryption. No one has posted the correct key though, so I fixed it. (You can use http://aesencryption.net/ to encrypt/decrypt with the algorithm I meant to use). Very sorry about this slip, and I hope that it didn't affect your analyses.