Secure communication is when two entities are communicating and do not want a third party to listen in. For this to be the case, the entities need to communicate in a way that is unsusceptible to eavesdropping or interception. Secure communication includes means by which people can share information with varying degrees of certainty that third parties cannot intercept what is said. Other than spoken face-to-face communication with no possible eavesdropper, it is probably safe to say that no communication is guaranteed to be secure in this sense, although practical obstacles such as legislation, resources, technical issues (interception and encryption), and the sheer volume of communication serve to limit surveillance. With many communications taking place over long distance and mediated by technology, and increasing awareness of the importance of interception issues, technology and its compromise are at the heart of this debate. For this reason, this article focuses on communications mediated or intercepted by technology. Also see Trusted Computing, an approach under present development that achieves security in general at the potential cost of compelling obligatory trust in corporate and government bodies. History In 1898, Nikola Tesla demonstrated a radio controlled boat in Madison Square Garden that allowed secure communication between transmitter and receiver. One of the most famous systems of secure communication was the Green Hornet. During WWII, Winston Churchill had to discuss vital matters with Franklin D. Roosevelt. In the beginning, the calls were made using a voice scrambler, as this was thought to be secure. When this was found to be untrue, engineers started to work on a whole new system, which resulted in the Green Hornet or SIGSALY. With the Green Hornet, any unauthorized party listening in would just hear white noise, but the conversation would remain clear to authorized parties. As secrecy was paramount, the location of the Green Hornet was only known by the people who built it and Winston Churchill. To maintain secrecy, the Green Hornet was kept in a closet labeled 'Broom Cupboard.'' The Green Hornet used a one-time pad. SIGSALY was also never broken. Nature and limits of security Types of security Security can be broadly categorized under the following headings, with examples: Hiding the content or nature of a communication Code – a rule to convert a piece of information (for example, a letter, word, phrase, or gesture) into another form or representation (one sign into another sign), not necessarily