2M. E. Hellman," The Extension of the Shannon Theory Approach to Cryptography". IEEE Transactions on Infor- mation Theory, v. IT - 23, n. 3, May 1977 : 289 - 294.
3T. Beth, M. Frisch, and G. J. Simmons, eds. , Lecture Notes in Computer Science 578;Public Key Cryptogra- phy:State of the Art and Future Directions, Springer - Verlag, 1992.
