Riff 1
e---------------------|----------------------
b---------------------|----------------------
g---------------------|----------------------
d-3-3---3-5-6-5-3-----|-3-3---3-5-6-5-3-2----
a-----------------3---|----------------------
e---------------------|----------------------

Riff 2
e---------------------|----------------------
b---------------------|----------------------
g---------------1-1---|-----0-0--------------
d-0h1-3-3---0h1-------|-0h1-------0h1-4-4----
a---------------------|----------------------
e---------------------|----------------------

Riff 3
e---------------------|----------------------
b---------------1-1---|-----0-0--------------
g-----2-2-------1-1---|-----0-0-------3-3----
d-0h1-3-3---0h1-------|-0h1-------0h1-4-4----
a---------------------|----------------------
e---------------------|----------------------

That's basically it. The bass line pretty much follows the guitar line.
Listen to the song to work out the correct structure.