Rapid hardware design for cryptographic modules with filtering structures over small finite fields

Abstract

This paper presents a design automation toolkit for hardware implementations of linear and non-linear feedback shift registers (FSRs). The toolkit is implemented in the GAP computer algebra system and generates both executable GAP code and VHDL for synthesizable hardware. To design an FSR, the user needs only to provide a template and instantiate a few parameters. The primary objects are LFSRs; NLFSRs; and arbitrary combinational functions, which are modelled as FILFUNs, for “filtering functions”. Conventional feedback functions are modelled as univariate or multivariate polynomials. More complex functions can be modelled as FILFUNs. The paper demonstrates the capabilities of the toolkit using the WG-7 and WG-8 keystream generators and the Grain v1 stream cipher. Less than 30 lines of GAP code are required to generate a complete datapath in VHDL.