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 probable 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 of the same type. In communications and information processing, encoding is the process by which information from a source is converted into symbols to be communicated. Decoding is the reverse process, converting these code symbols back into information understandable by a receiver. One reason for coding is to enable communication in places where ordinary spoken or written language is difficult or impossible. For example, semaphore, where the configuration of flags held by a signaler or the arms of a semaphore tower encodes parts of the message, typically individual letters and numbers. Another person standing a great distance away can interpret the flags and reproduce the words sent. Obfuscation Encryption Steganography Identity Based Hiding the parties to a communication – preventing identification, promoting anonymity "Crowds" and similar anonymous group structures – it is difficult to identify who said what when it comes from a "crowd" Anonymous communication devices – unregistered cellphones, Internet cafes Anonymous proxies Hard-to-trace routing methods – through unauthorized third-party systems, or relays Hiding the fact that a communication takes place "Security by obscurity" – similar to needle in a haystack Random traffic – creating random data flow to make the presence of genuine communication harder to detect and traffic analysis less reliable Each of the three types of security is important, and depending on the circumstances, any of these may be critical. For example, if a communication is not readily identifiable, then it is unlikely to attract attention for identification of parties, and the mere fact a communication has taken place (regardless of content) is often enough by itself to establish an evidential link in legal prosecutions. It is also important with computers, to be sure where the security is applied, and what is covered.
Borderline cases A further category, which touches upon secure communication, is software intended to take advantage of security openings at the end-points. This software category includes trojan horses, keyloggers and other spyware. These types of activity are usually addressed with everyday mainstream security methods, such as antivirus software, firewalls, programs that identify or neutralize adware and spyware, and web filtering programs such as Proxomitron and Privoxy which check all web pages being read and identify and remove common nuisances contained. As a rule they fall under computer security rather than secure communications.
Tools used to obtain security
Encryption
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