Paper 3, Section II, H

Coding \& Cryptography
Part II, 2018

Compute the rank and minimum distance of the cyclic code with generator polynomial g(X)=X3+X2+1g(X)=X^{3}+X^{2}+1 and parity check polynomial h(X)=X4+X3+X2+1h(X)=X^{4}+X^{3}+X^{2}+1. Now let α\alpha be a root of g(X)g(X) in the field with 8 elements. We receive the word r(X)=X2+X+1r(X)=X^{2}+X+1 (modX71)\left(\bmod X^{7}-1\right). Verify that r(α)=α4r(\alpha)=\alpha^{4}, and hence decode r(X)r(X) using minimum-distance decoding.