1. A method of securing data, comprising: receiving plain text, a secret key and a primitive polynomial that defines a finite field of even characteristic; dividing the plain text into a plurality of plain text blocks; and for each plain text block of the plurality of plain text blocks other than a first plain text block: multiplying the plain text block by a preceding cipher text block over the finite field of even characteristic, modulo the primitive polynomial, to generate an intermediate block, wherein the preceding cipher text block was generated from a preceding plain text block; and processing the intermediate block by a block cipher using the secret key to generate a subsequent cipher text block, wherein the block cipher operates in a nonlinear feedback mode of operation.