Composite Field Mapping Example.pdf - An example showing how matrices used for mapping between GF(2^8) and a composite field GF(((2^2)^2)^2) are generated, and the logic behind those mapping matrices. The matrices used in this example are the ones seen on page 4, matrix (8) and page 5, matrix (10) of this reference:
A reference implementation of the AES S-Box pdf
wldnrpt.pdf - a 1995 report by professor E J Weldon Jr, explaining inversion (1/x) of elements GF(2^8) via mapping to GF((2^4)^2), doing the inversion algebra, and mapping back.