Cryptographic key assignment scheme for overcoming the incorrectness of the CHW scheme

Based on the Newton interpolation method and a predefined one-way function, a cryptographic key assignment scheme, called the CHW scheme, in a user hi erarchy was presented by Chang et al. in 1992. The CHW scheme did not need the large amount of storage needed in the Akl-Taylor scheme. However, two c ounter-examples have been presented to prove the incorrectness of the CHW s cheme, and further two modified versions of the CHW scheme were also proven to be insecure. Owing to these problems, a simple scheme is proposed to ov ercome the incorrectness and to enhance the security of the CHW scheme.