Jointly with his coauthors, Cunsheng Ding has founded the stability theory for stream ciphers, which includes a number of new measures on the security of stream ciphers. Among them is the sphere complexity whose variant is called the k-error linear complexity and is intensively studied. His works on the stability theory of stream cipher jointly with his coauthors are mainly documented in a few papers and the following two research monographs and have been citied over 1000 times by others.
C. Ding, G. Xiao and W. Shan, The Stability Theory of Stream Ciphers, Lecture Notes in Computer Science, Vol. 561, Springer Verlag, 1991.
T. W. Cusick, C. Ding and A. Renvall, Stream Ciphers and Number Theory, North-Holland Mathematical Library, Vol. 55, Elsevier, 1998.
Since 1991, a number of people have worked on this topic and made a lot of progress. Now the stability theory of stream ciphers is much enhanced.
Lecture slides on the Stability Theory of Stream Ciphers