Quadibloc 2002E is designed to have a simpler and more uniform structure than Quadibloc 2002 and other designs of mine, but remain highly resistant to attack. It has three basic round types. Two of them are modified from the Quadibloc 2002A round; the diffusion phase comes in two varieties, one of which involves subkeys and twice the number of rounds within the transforms. The other round type has an overall structure similar to the Quadibloc 2002D round; however, it makes extensive use of the "fractal Feistel" principle, and that has resulted in the round becoming quite large and complex. As a result, the description of this block cipher has been split over several pages.
A variant of this cipher including only the first two round types is described as Quadibloc 2002E SR; this already can be considered a more complicated development of Quadibloc 2002A. As well, modifications of this cipher which operate on a 256-bit block are outlined as Quadibloc 2002E W and Quadibloc 2002E WS, among others.
Simply using the standard rounds in a cipher that would be a slightly more elaborate version of Quadibloc 2002A would already, of course, create a block cipher of some interest, leaving aside the rounds using the fractal Feistel principle, which I refer to as the "cryptographic core" rounds, using a term coined by the inventors of MARS. Also, as it happens, the greater diffusion phase, and the overall f-function for the core rounds both use 32 subkeys, so it is tempting to consider a simplification of this design that replaces the bulkiest use of the fractal Feistel principle. Thus, even if the design is not practical as it stands, elements of it might be used in more practical designs.
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