Many books on privacy do little more than assert — or dismiss — the claims of national security and law enforcement. Privacy on the Line takes a serious look at both. A long chapter on national security covers the history of communications and signal intelligence and the role cryptography plays in them. A chapter on law enforcement introduces wiretaps and pen registers and other forms of surveillance.
After this "digression", Diffie and Landau return to the history of privacy in the United States. They trace the legal and political protections for and threats to privacy, from the Bill of Rights, through the Second World War, the McCarthy era, and the Vietnam war period, up to the present. This is followed by a chapter more specifically on wiretapping, covering the history of its regulation and abuse — the introduction of the telegraph, the Olmstead and Nardone cases, Hoover and the FBI, organized crime, Title III, "domestic national security", Watergate, and the Foreign Intelligence Surveillance and Electronic Communications Privacy Acts. Chapters on communications and cryptography present the most recent events and the current situation. The first covers the Digital Telephony saga and the debate about the effectiveness of wiretaps and the extent to which they are being hindered by technological advances. The second covers PGP, Clipper and key escrow, the NSA and NIST and their relationship, and international developments in cryptography policy.
A final chapter argues that technological advances have on the balance put law enforcement and national security in a stronger position, not a weaker one, and that even with wiretapping the effects are mixed. Diffie and Landau conclude that "government efforts to keep honest citizens from using cryptography to protect their privacy continue. Such efforts are unlikely to achieve what governments claim to want, but very likely to cause serious damage to both business and democracy in the process."
Privacy on the Line is an accessible general introduction to a topic of increasing prominence. I recommend it to anyone who wants a balanced introduction to the history and current status of communications privacy. And those already familiar with the subject may find new insights in its analysis.