Long before the advent of electronic systems, different methods of information scrambling were used. Early attempts at data security in electronic computers employed some of the same transformations. Modern secret key cryptography brought much greater security, but eventually proved vulnerable to brute-force attacks. Public key cryptography has now emerged as the core technology for modern computing security systems. By associating a public key with a private key, many of the key distribution problems of earlier systems are avoided. The Internet public key infrastructure provides the secure digital certification required to establish a network of trust for public commerce. This paper explores the details of the infrastructure.