Periodic sequences with maximal linear complexity and almost maximal k-rrror linear complexity

C. Ding, W. Shan and G. Xiao conjectured a certain kind of trade-off between the linear complexity and the k-error linear complexity of periodic sequences over a finite field. This conjecture has recently been disproved by the first author, by showing that for infinitely many period lengths N and some values of k both complexities may take very large values (contradicting the above conjecture). Here we use some recent achievements of analytic number theory to extend the class of period lengths N and the number of admissible errors k for which this conjecture fails for rather large values of k. We also discuss the relevance of this result for stream ciphers.