1. A method of securing data, comprising: dividing received plain text into a plurality of plain text blocks by a computing device executing a block cipher; and for each plain text block of the plurality of plain text blocks other than a first plain text block: determining a number of bits to rotate for at least one of the plain text block or a preceding cipher text block generated from a preceding plain text block based on at least one of a first secret bit sequence received from a stream cipher or a second secret bit sequence computed from a preceding cipher text block; rotating bits of at least one of the plain text block or the preceding cipher text block by the determined number of bits; multiplying the plain text block by the preceding cipher text block over a finite field of even characteristic, modulo a primitive polynomial that defines the finite field of even characteristic, to generate an intermediate block; and processing the intermediate block by the block cipher using a received secret key to generate a subsequent cipher text block, wherein the block cipher operates in a nonlinear feedback mode of operation.