This chapter provides a more thorough introduction to cryptography, authentication, and access control than was given in chapter 2. For in-depth studies of these areas we refer to some books in the area. Security in Computing by Pfleeger [Pfl97] presents a general overview of the area. Schneier's Applied Cryptography is a comprehensive volume on cryptography that also includes code examples [Sch95]. Salomaa gives an easy to read, but yet comprehensive, introduction to public-key cryptography in general in [Sal90,Sal96]. In her doctoral thesis, Digital Signature Schemes, Pfitzmann covers in depth the theory and use of digital signatures [Pfi96]. In Authentication Systems for Secure Networks, Oppliger surveys authentication frameworks in use today [Opp96].