I have two problems:

1) Identify Aut(Aut($\displaystyle \mathbb{Z}_8$))

I know that Aut($\displaystyle \mathbb{Z}_8$) is isomorphic to $\displaystyle \mathbb{Z}_2 \oplus \mathbb{Z}_2 $ but what about Aut(Aut($\displaystyle \mathbb{Z}_8 $))?

2) Identify Aut G, where G=({1, 3, 5, 7}, $\displaystyle ._8$).

{1, 3, 5, 7} are generators of $\displaystyle \mathbb{Z}_8 $ so I'm guessing I should head in that direction, but don't know how.

Please help.