Symmetric Key Crypto
Mark Stamp · Information Security · 2005
There are two distinct classes of symmetric ciphers, stream ciphers and block ciphers. Stream ciphers generalize the one-time pad, where provable security is traded for practicality, while block ciphers can be viewed as the “electronic” equivalent of a classic codebook ciphers. In this chapter, we discuss both of these classes of symmetric ciphers, but we concentrate on block ciphers since they are more prevalent today. We spend some time discussing the Data Encryption Standard, or DES, the granddaddy of all modern block ciphers, and we briefly cover a few other well-known block ciphers, including Advanced Encryption Standard (AES) and the Tiny Encryption Algorithm (TEA). We show how block ciphers can be used for data integrity using a “message authentication code”, or MAC, as well as for confidentiality. Symmetric ciphers are also useful in authentication protocols, as we'll see in later chapters.