EN
Let q > 2 be a prime power and $f = -x + tx^{q} + x^{2q-1}$, where $t ∈ 𝔽*_{q}$. We prove that f is a permutation polynomial of $𝔽_{q²}$ if and only if one of the following occurs: (i) q is even and $Tr_{q/2}(1/t) = 0$; (ii) q ≡ 1 (mod 8) and t² = -2.