Cryptography & Pretty Good Privacy (PGP)

1. The need for cryptography in electronic communications

Cryptography has been around for centuries; as long as there has been communication, there has been the need for privacy and safe, secure methods of transmission. Although many types of difficult problems can be classified as cryptography problems, what we are mostly concerned with today is the ability to keep transmissions private through the use of data encryption techniques. This has become an even greater issue due to the changing nature of communications since the information revolution. More and more people rely on electronic communications for the transmission of sensitive or personal data; e-mail, e-commerce, FTP, and HTML are all examples of technology that have already filtered into the social consciousness as primary ways for disseminating and gathering information and for exchanging goods and services. While this technological shift has made communication faster, easier, and better in many ways, it has also brought along with it a whole host of difficult problems and social policy issues.

The main problem that comes with electronic communications is the ease with which transmissions can be eavesdropped or impersonated. Paper communications obviously have security problems as well: documents can be stolen, steamed open, have forged signatures or changed contents. However, if someone is trying to catch a specific transmission (or type of communication), it is much easier when dealing with an electronic medium. It is a trivial matter for people to set up programs that systematically scan e-mail for keywords, or that sniff packets in a Telnet session for passwords, whereas randomly steaming open mass quantities of paper mail looking for a certain document is clearly infeasible. Also, since there can be (and often are) multiple copies of any given electronic transmission, it is difficult to know if someone has stolen a copy or somehow altered the original.

Secondly, there is an access control problem. Many electronic transmissions are made in a broadcast manner, as seen with cable or satellite television and wireless phones. People can install devices to intercept these transmissions, and senders usually have no way to either monitor or stop this. In order to prevent unwanted people from making free use of their services, senders must encrypt their outgoing transmissions. To their paying customers, they can give special devices to decrypt the information.

Finally, there is the problem of authentication: electronic communications are impersonal, and can be easily forged by impersonating IP addresses, changing "sender fields" in e-mail, "cloning" cellular phone numbers, and so forth. In order for people to want to - and, indeed, be able to - use electronic communication in the coming years, it is essential that these problems be resolved. Right now, advances in cryptography are the best way to address these issues. Data encryption not only provides privacy and access control by rendering communications illegible to unauthorized parties; it can provide effective authentication as well through the use of digital signatures and timestamps.

2. The primary forms of cryptography