## CryptoDB

### Xiwang Cao

#### Publications

**Year**

**Venue**

**Title**

2010

EPRINT

On the order of the polynomial $x^p-x-a$
Abstract

In this note, we prove that the order of $x^p-x-1\in \F_p[x]$ is
$\frac{p^p-1}{p-1}$, where $p$ is a prime and $\mathbb{F}_p$ is the
finite field of size $p$. As a consequence, it is shown that
$x^p-x-a\in \mathbb{F}_p[x]$ is primitive if and only if $a$ is a
primitive element in $\mathbb{F}_p$.

2010

EPRINT

On Exponential Sums, Nowton identities and Dickson Polynomials over Finite Fields
Abstract

Let $\mathbb{F}_{q}$ be a finite field, $\mathbb{F}_{q^s}$ be an extension of $\mathbb{F}_q$, let $f(x)\in \mathbb{F}_q[x]$ be a polynomial of degree $n$ with $\gcd(n,q)=1$. We present a recursive formula for evaluating the exponential sum $\sum_{c\in \mathbb{F}_{q^s}}\chi^{(s)}(f(x))$. Let $a$ and $b$ be two elements in $\mathbb{F}_q$ with $a\neq 0$, $u$ be a positive integer. We obtain an estimate of the exponential sum $\sum_{c\in \mathbb{F}^*_{q^s}}\chi^{(s)}(ac^u+bc^{-1})$, where $\chi^{(s)}$ is the lifting of an additive character $\chi$ of $\mathbb{F}_q$. Some properties of the sequences constructed from these exponential sums are provided also.

#### Coauthors

- Lei Hu (1)