# Applications of GF(p) polynomials

A Galois field of the type $GF(p)$, where $p$ is prime, is normally expressed as the ring of integers modulo $p$.

If my understanding is correct, it is also possible to represent its elements as a ring $\mathbb Z_2[X]$ of polynomials defined over $GF(p)$, i.e. for $GF(2)$, we'd have polynomials of the form similar to $x^8+x^5+x^3+1$ or $x^9+x^6+x^2$, etc, and for $GF(5)$, we'd have polynomials of the form similar to $4*x^7+2*x^3+3*x+1$ or $2*x^5+3*x^3+x^2$, etc. All arithmetic operations are like with normal polynomials, but with a difference: all arithmetic operations on coefficients which occur in the calculations are done modulo $p$.

The question is: do polynomials defined over $GF(p)$ have any real application in cryptography where they are a better fit than their integers-modulo-$p$ counterparts?

Please correct me if I mixed something up in the theoretical part!

• Lots of applications, including error correction and secret sharing. – Vadym Fedyukovych Jan 28 '15 at 17:06
• Elements of $\mathrm{GF}(p^k)$ are usually represented as polynomials with coefficients in of $\mathrm{GF}(p)$. More generally, fields and polynomials are very closely related. – fkraiem Jan 28 '15 at 22:49

In my knowlegde, XTR is a cryptosystem build over $GF(p^6)$. We however use the subfield $GF(p^2)$ to have a compact representation. I don't know if there are other cryptosystems defined directly on Galois field extention, but using some tools are common. For that, take a look on the operative environment of Weil or Tate pairing.