Some of the many types of information secured by cryptography are copyrighted data, business data, anonymous cash, espionage, illegal data, anonymous data, age or location controlled data, voice data, and illegal markets. This list is not exhaustive, however it provides a good starting point to begin discussion. Early pioneers of public cryptosystems predicted legal problems developing in these areas and without fail each area has been challenged by those who want public use of them controlled.
In the area of copyrighted information, as in most areas, cryptography is a two-sided sword. Content manufactures, or companies whose products are intangible intellectual creations like movies and books, control their content through copyright and are increasingly looking toward encryption to control how their works are used. In theory, any cryptosystem designed to deliver content to consumers while simultaneously protecting it from those consumers is doomed to fail, because at some point the content needs to be decrypted to be viewable. In practice it appears to work quite well, because the effort required to find a way to get at the decrypted content provides a high bar for entry. The flip side of the blade, however, is the use of cryptosystems to illegally traffic these copyright-protected works and anonymize the distribution such that the copyright owner's control is weakened.
In the area of business data, cryptosystems can protect businesses from criminal mischief as well as protect such businesses from government intrusion. For instance, hospital and health care records are held to extremely high standards of protection against unauthorized disclosure. Encrypted communication lines are extremely important tools in the arsenal of hospitals, when used to get medical information where it needs to go quickly without compromising its security. On the other hand, businesses can use such secure lines for illegal activities such as to coordinate prices, trade insider information, or double book and keep the second book private.
Anonymous currency, or money that is not easily traceable, is an important form of information for those who want to escape government interference. The idea is that through cryptosystems, a trusted authority can digitally sign bank notes to give them value as money. Although similar to other non-official tender, this has the benefit of being easy to create, extremely difficult to counterfeit, liquid, and not linked to an identity. It can be used to facilitate money laundering and tax evasion.
Espionage is the bane of governments, corporations, and individuals. Spy-craft necessitates the need for anonymity and secrecy. Keeping secrets is inherent to the nature of this business and not much more needs to be said about it.
Some forms of information, with or without encryption, can be in itself illegal. This includes obvious examples such as sexually explicit depictions of underage children, but it can also included computer programs with the potential to view DVDs. While programmers contend that writing in a language computers understand exercises free speech and should be protected as such, the US courts have disagreed on how far that protection extends, leading to programs such as a DVD reader for Linux to be declared illegal. Creators and consumers of this type of information may use cryptosystems to protect themselves from those who control this type of information.
Anonymous information is often of general importance. For instance, e-mails with no identifiable sender can be sent through a re-mailer network. These networks consist of nodes that know only enough about the message to send it on to the next node or to the final destination. This is typically done with a technique called onion routing, where the message is encrypted and the instructions for each node that passes the message is appended to the message and encrypted again such that the node can decrypt it. Thus, each messenger peels off a layer of the onion by decrypting it with the messenger's private key and reveals only enough information to pass the message on to the next node. Other anonymous networks are more sophisticated, such as freenet, which affords completely anonymous publishing of information into the system.
Voice information, such as digital cell phone calls, are encrypted. This allows users to converse with relative certainty that their conversations are not being overheard. Other methods of conversing using voice include programs that allow you to talk over the Internet. Typically that technology falls under the umbrella VOIP, or Voice Over Internet Protocol. The main threat to the security of VOIP is the government attempting to regulate these programs much like they regulate normal phone carriers: by taxing them and requiring wiretap ability. The government contends that this is merely a logical extension of the already existing ability to tap cell phones and land lines. Privacy advocates counter with the assertion that originally the government could not listen in on any conversations at all before there were telephones, and the logical extension of that is there should be no government capacity for eavesdropping at all.
Illegal markets are another area where cryptography can play a protective role. Cryptosystems can hinder government interference in such markets. These are markets on illegal information, i.e., ``futures markets'' on the lifespans of undesirable people, otherwise known as hiring an assassin, and other markets involving criminal intent.