Inversion Attack

Related Concepts

Filter Generator; Stream Cipher

Definition

The inversion attack is a known plaintext attack on some particular filter generators. It was proposed by Golić in 1996 [1]. A generalization to any filter generator, called generalized inversion attack, was presented by Golić, Clark, and Dawson in 2000 [2]. Both inversion attack and generalized inversion attack aim at recovering the initial state of the linear feedback shift register (LFSR) from a segment of the running-key when the LFSR feedback polynomial, the tapping sequence, and the filtering function are known.

Theory

Original Inversion Attack

The original inversion attack only applies when the filtering function f is linear in its first input variable (forward attack) or in its last input variable (backward attack), i.e., when

$$f({x}_{1},{x}_{2},\ldots, {x}_{n}) = {x}_{1} + g({x}_{2},\ldots, {x}_{n})$$

or

$$f({x}_{1},{x}_{2},\ldots, {x}_{n}) = g({x}_{1},\ldots, {x}_{n-1}) + {x}_{n}$$

where $g$ is a Boolean function...