I am working on finding the multiplicative reverse in GF(28) using the Euclidean Algorithm but after reading multiple sources, I feel as though I am proceeding incorrectly. Using the irreducible polynomial m(p)=x8+x4+x3+x+1=0x11B I am trying to find the inverse of x6+x4+x+1=0x53
I know using long division (via http://www.wolframalpha.com/widgets/view.jsp?id=f396eaca9aaccbf858652bccc972324a) I get for the first step
(x8+x4+x3+x+1)=(x6+x4+x+1)∗(x2−1)+(2x4−x2+2x+2)
but do I keep the negatives and even coefficients? I can't seem to get a reasonable answer and all the examples I have seen use simpler numbers. I know the answer to be x7+x6+x3+x=0xCA I just cannot seem to get there.
Answer
Here are the steps you should obtain.
x8+x4+x3+x+1=(x6+x4+x1+1)(x2+1)+x2x6+x4+x+1=x2(x4+x2)+x+1x2=(x+1)x+1.
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