galois field arithmetic.htm
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<H1><A name=SECTION00020000000000000000>Galois Field Arithmetic</A></H1>
<P>Galois Fields = fields of finite order (cardinality). <BR>Notation:
GF(<I>q</I>) = Galois field of order <I>q</I>.<BR>
<P><B>Theorem</B>: The integers <IMG height=27 alt=tex2html_wrap_inline286
src="Galois Field Arithmetic_ficheiros/img2.gif" width=112 align=middle> where
<I>p</I> is a prime, form the field GF(<I>p</I>) under <I>modulo p</I> addition
and multiplication.<BR>
<P><B>Definition</B>: Let <IMG height=29 alt=tex2html_wrap_inline292
src="Galois Field Arithmetic_ficheiros/img3.gif" width=11 align=middle> be an
element in GF(<I>q</I>). The order of <IMG height=29 alt=tex2html_wrap_inline292
src="Galois Field Arithmetic_ficheiros/img3.gif" width=11 align=middle> is the
smallest positive integer <I>m</I> such that <IMG height=29
alt=tex2html_wrap_inline300 src="Galois Field Arithmetic_ficheiros/img4.gif"
width=59 align=middle> . <BR>
<P><B>Theorem</B>: If <IMG height=32 alt=tex2html_wrap_inline302
src="Galois Field Arithmetic_ficheiros/img5.gif" width=88 align=middle> for some
<IMG height=32 alt=tex2html_wrap_inline304
src="Galois Field Arithmetic_ficheiros/img6.gif" width=88 align=middle> , then
<IMG height=32 alt=tex2html_wrap_inline306
src="Galois Field Arithmetic_ficheiros/img7.gif" width=81 align=middle> .<BR>
<P><B>Definition</B>: An element with order (<I>q</I>-1) in GF(<I>q</I>) is
called a <I>primitive element</I> in GF(<I>q</I>).<BR>
<P>Every field GF(<I>q</I>) contains at least one primitive element <IMG
height=9 alt=tex2html_wrap_inline316
src="Galois Field Arithmetic_ficheiros/img8.gif" width=10 align=bottom> .<BR>All
nonzero elements in GF(<I>q</I>) can be represented as (<I>q</I>-1) consecutive
powers of a primitive element <IMG height=9 alt=tex2html_wrap_inline322
src="Galois Field Arithmetic_ficheiros/img9.gif" width=20 align=bottom>
<P><IMG height=21 alt=displaymath278
src="Galois Field Arithmetic_ficheiros/img10.gif" width=423 align=bottom>
<P>
<P><B>Theorem</B>: The order <I>q</I> of a Galois Field GF(<I>q</I>) must be a
power of a prime.
<P><BR>
<HR>
<UL>
<LI><A
href="http://www.ee.ucla.edu/~matache/rsc/node3.html#SECTION00021000000000000000"
name=tex2html34><B>Polynomials over Galois Fields</B></A>
<LI><A
href="http://www.ee.ucla.edu/~matache/rsc/node4.html#SECTION00022000000000000000"
name=tex2html35><B>Construction of Galois Field GF(2^m)</B></A> </LI></UL><BR>
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<P>
<ADDRESS><I>A. Matache <BR>Sun Oct 20 17:42:25 PDT 1996</I>
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