An algebraic attack on stream ciphers with application to nonlinear filter generators and WG-PRNG

In this paper, we propose a new algebraic attack on stream ciphers. Starting from the well-known attack due to Courtois and Meier, we design an attack especially effective against nonlinear filter generators. We test it on two toy stream ciphers and we show that the level of security of one of stream ciphers submitted to the NIST competition on Lightweight Cryptography, WG-PRNG, is less than that stated before now.