Under which condition is $f : x \mapsto x^e \mod n$ invertible?
I mean, for each distinct $x \in \{0, 1, 2, \ldots, n-1\}$ the result is distinct?
Is that $e$ must be coprime with the totient of $n$ ($\varphi(n)$)?
I read several articles on RSA, but this point is still not clear to me.
