Guang Gong and Lein Ha proposeda new Diffie-Hellman public-key distribution schemethat is based on third-order linear feedback shift reg-ister sequences over GF(p) and its security is basedon the difficulty of solving the discrete logarithm inGF(p3). However, a method for attacking the schemeis presented in this paper. Despite that the methodcould not break up it fully, it indicates that the se-curity of the scheme is likely to be not being basedon the difficulty of solving the discrete logarithm inGF(p3). With this method, we have also obtained theweak private keys of the scheme.