Nonlinear-Feedback Shift Registers for Stream Ciphers

The analysis of shift registers with nonlinear feedbacks was carried out for the possibility of their use as cryptographically strong components of stream ciphers. The use of these registers is particularly relevant for the design of low-resource cryptography and is used to protect the transmitted data on the Internet of Things. Considering the diversity of possible cryptographic attacks on this element, some of the main properties were considered in the work, such as nonlinearity, correlation immunity, and the possibility of choosing NLFSRs optimized for these indicators and at the same time having minimal structural complexity. In addition, such parameters as the balance of the formed sequence and the presence of prohibitions are considered. Full set of possible shift registers with nonlinear feedback has analyzed in this paper. This set is forming the sequence of the maximum period for a register dimension not exceeding six cells, as well as registers with a nonlinearity not higher two with register dimension from seven to nine cells.