This chapter is from the book
This chapter is from the book
This chapter is from the book
17.7 Conclusion
In this chapter we have presented the basic model and goals of the cryptographic process. We looked at some early cipher systems and reviewed the mathematical theory of secret communications established by Shannon. We defined a system that can exhibit perfect secrecy and established that such systems can be implemented but that they are not practical for use where high-volume communications are required. We also considered practical security systems that employ Shannon’s techniques (known as confusion and diffusion) to frustrate the statistical endeavors of a cryptanalyst.
The outgrowth of Shannon’s work was utilized by IBM in the LUCIFER system, which later grew into the National Bureau of Standards’ Data Encryption Standard (DES). We outlined the DES algorithm in detail. We also considered the use of linear feedback shift registers (LFSR) for stream encryption systems, and demonstrated the intrinsic vulnerability of an LFSR used as a key generator.
We also looked at the area of public-key cryptosystems and examined two schemes, the Rivest–Shamir–Adelman (RSA) scheme, based on the product of two large prime numbers, and the Merkle-Hellman scheme, based on the classical knapsack problem. Finally, we looked at the novel scheme of Pretty Good Privacy (PGP), developed by Phil Zimmerman and published in 1991. PGP utilizes the benefits of both private and public-key systems and has proven to be an important file-encryption method for sending data via electronic mail.