Gong, Xinxin, and Bin Zhang. “Comparing Large-Unit and Bitwise Linear Approximations of SNOW 2.0 and SNOW 3G and Related Attacks”. IACR Transactions on Symmetric Cryptology, vol. 2021, no. 2, June 2021, pp. 71-103, doi:10.46586/tosc.v2021.i2.71-103.