  As a research field of stream ciphers, the pursuit of a balance of security
and practicality is the focus. The conditions for security usually have to
satisfy at least high period and high linear complexity. Because the
feedforward clock-controlled structure can provide quite a high period and
utility, many sequence ciphers are constructed based on this structure.
However, the past study of its linear complexity only works when the controlled
sequence is an m-sequence. Using the theory of matrix over the ring and block
matrix in this paper, we construct a more helpful method. It can estimate the
lower bound of the linear complexity of the feedforward clock-controlled
sequence. Even the controlled sequence has great linear complexity.
