1. National Bureau of standards, ”Encryption algorithm for computer data protection: Requests for comments,” Federal Register, Vol. 40. No. 12134, 1975.
2. Diffie, W. and Hellman, M. E., ”Exhaustive cryptanalysis of the NBS Data Encryption Standard,” computer magazine, 10, 6, 74–84, 1977.
3. Punckuell, D. A. and Eshraghian, K., Basic VLSI Design (principles and applications), Prentice-Hall of Australia, 1985.
4. Hendessi, F., Cryptanalysis of the Data Encryption Standard, Master Thesis, Department of Electrical Engineering, Isfahan Univ. of Tech., Isfahan, Iran, 1989.
5. National Bureau of standards, ”Specification for the Data Encryption Standard,” Federal Register, Vol. 46, January 1977.