Erik Zenner Matthias Krause Stefan Lucks Improved Cryptanalysis of the Self-Shrinking Generator. 21-35 2001 conf/acisp/2001 ACISP http://link.springer.de/link/service/series/0558/bibs/2119/21190021.htm db/conf/acisp/acisp2001.html#ZennerKL01