# Elliptic curve over prime field with high order roots of unity

Suppose I have an elliptic curve defined over a prime field $$\operatorname{GF}(p)$$ where $$p$$ is a large prime (e.g. 256-bit). Suppose also that $$p = kn +1$$, where $$n$$ is a relatively large power of $$2$$ (e.g. $$2^{32}$$). This structure implies that $$\operatorname{GF}(p)$$ has $$n^{\mathit{th}}$$ roots of unity.

My question is: does the fact that $$\operatorname{GF}(p)$$ has "high order" roots of unity make curves defined over this field inherently less secure?

My question is: does the fact that $$\operatorname{GF}(p)$$ has "high order" roots of unity make curves defined over this field inherently less secure?
Not particularly; the factorization of $$p-1$$ is not specifically relevant to the strength of a curve over $$\operatorname{GF}(p)$$.
Now, it is quite relevant to the strength of the group $$\mathbb{Z}_p^*$$; however that's because the order of the group is always $$p-1$$ (assuming $$p$$ is prime), and the factorization of the group order is quite relevant. However, the elliptic curve (in general) doesn't have order $$p-1$$; instead, it is $$p + \delta$$ for some $$|\delta| < 2\sqrt{p}$$ (the exact value of $$\delta$$ depends on the precise curve you pick), and it is the factorization of $$p + \delta$$ which is important.
• @irakliy: there's the NIST curve P-224, which has $p = 2^{224} - 2^{96} + 1$; that certainly has high roots of unity for large powers of 2. BTW: why is that important to you? – poncho May 20 at 19:26