Periodic sequences with maximal -adic complexity and large -error -adic complexity over

Abstract: Complexity measures for keystream sequences over play a crucial role in designing good stream cipher systems. This correspondence shows a general upper bound on -error -adic complexity of periodic sequences over , and establishes the existence of periodic sequences over which simultaneously possess maximal -adic complexity and large -error -adic complexity. Under some conditions the overwhelming majority of all -periodic sequences over with maximal -adic complexity have a -error -adic complexity close to . The existence of many such sequences thwarts attacks against the keystreams by exhaustive search. [Copyright &y& Elsevier]