Analysis of secure signature codes provided by bent sequences for a CDMA system

Matsufuji and Imamura (see IEEE Trans. on Info. Theory, vol.46, no.4, p.1691-95, 2000) proposed a new method to generate an optimal set of bent sequences as a set of signature sequences for a CDMA system has been introduced. This method is designed to make the CDMA system secure against interception, for both an insider intruder (a user) and an outsider intruder. The security analysis of this system of Matsufuji et al. was based on computing the cardinality of the search space. In this paper after reforming the bent function decomposition, we reapply the above analysis to the system. Then for binary sequences, we consider another analysis to this system, which is based on the fact that all the sequences in the search space do not have equal worthiness for the intruder. Moreover, another application of the signature assignment algorithm to provide multi-level security is presented.