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

Based on Newton´s interpolation method and a predefined one-way function, a cryptographic key assignment scheme, called the CHW scheme, in a user hierarchy was presented by Chang et al. (1992). The CHW scheme did not need the large amount of storage needed in the Akl-Taylor (1983) scheme. However, two counter-examples have been presented to prove the incorrectness of the CHW scheme, 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 overcome the incorrectness and to enhance the security of the CHW scheme