  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.
