From the foreward to "Contemporary Cryptography" by Rolf Oppliger:

Assume for a moment that everything in this book was known for decades but not widely published.  If I owned this book in the early nineteen-eighties, some governments would consider me dangerous (certainly more dangerous than anyone reasonably considers me now). The reason? Cryptography - the ability to encipher messages - was considered an instrument of war and espionage. Some countries (the USA included) considered export of cryptographic mechanisms to be in the same category of crime as smuggling nuclear weapons! This was desipite the fact that cryptology has been studied and practiced for thousands of years around the world.

In the year two thousand five, a mere twenty years later, things are somewhat less extreme, and I have shelves full of books on cryptography. However, many governments still fear the spread of encryption and thus severely restrict (or prohibit) its use within their borders. This is despite its regular use billions of times per day in everything from banking networks to medical records to cable TV systems to Internet commerce over the WWW, as well as governmental uses.

Why is the knowledge of cryptography so often feared by those in authority? One explanation may be that it is because cryptography can be used to hide criminal behavior, espionage, and political activities. More generally, it helps to remove information from the purview of the state, and this can be threatening to governments whose survival is based on restricting citizens' knowledge. Information can be used or misused in so many ways it is no wonder that protecting it is of widespread interest.

At its heart, cryptography is concerned with information, whether stored as data, or communicated to others. In turn, information and communication undergird nearly everything we do. Commerce is driven by communication of finance and sales, research is based on data acquisition and reference, and government functions on the collection and processing of records. Enthertainment is encoded information, whether presented as music, paintings, or the performance of a play. Civilization is enabled by our ability to communicate information to each other, and to store it for later use. ...

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The more deeply you pursue this trail of information, the more connections one finds. It is clear that our ability to store and communicate information is fundamental to much more than most of us realize. Furthermore, knowing some of that information at the right time can provide tremendous advantage, whether it is in personal relationships, commercial enterprise, or acts by nation-state leaders. It therefore follows that means of protecting that information from disclosure or alternation are often as valuable as the information itself - if not more so.

It is here that cryptography comes into play. With good cryptography, we may be able to protect sensitive information: without it, we are all disadvantaged. It should thus be no surprise that so many organizations have tried to restrict cryptography such that they were the sole practitioners. History continues to show that such efforts seem destined to (eventually) fail. For uses good and ill, cryptography is around to stay.