Chapter Four. Asymmetric Cryptography

Modern computing has generated a tremendous need for convenient , manageable encryption technologies. Symmetric algorithms, such as Triple DES and Rijndael, provide efficient and powerful cryptographic solutions, especially for encrypting bulk data. However, under certain circumstances, symmetric algorithms can come up short in two important respects: key exchange and trust. In this chapter we consider these two shortcomings and learn how asymmetric algorithms solve them. We then look at how asymmetric algorithms work at a conceptual level in the general case, with emphasis on the concept of trapdoor one-way functions. This is followed by a more detailed analysis of RSA, which is currently the most popular asymmetric algorithm. Finally, we see how to use RSA in a typical program using the appropriate .NET Security Framework classes.

We focus on the basic idea of asymmetric algorithms, and we look at RSA in particular from the encryption/decryption point of view. In Chapter 5 we explore using the RSA and DSA asymmetric algorithms as they relate to authentication and integrity checking, involving a technology known as digital signatures. For a more thorough discussion of RSA from a mathematical point of view, please see Appendix B.