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The National Security Agency (NSA) is a United States government agency responsible for both the collection and analysis of message communications, and for the security of government communications against similar agencies elsewhere. It is a part of the Department of Defense. Its eavesdropping brief includes radio broadcasting, both from organizations and individuals, the Internet, and other intercepted forms of communication, especially confidential communications. Its secure communications brief includes military, diplomatic, and all other sensitive, confidential or secret government communications. Despite being the world's largest single employer of Ph.D. mathematicians, the owner of the single largest group of supercomputers, and having a budget rather larger than that of the CIA, it has had a remarkably low profile until recent years. For a long time its existence was not even admitted by the US government. The acronym "NSA" has jokingly been morphed to mean No Such Agency and Never Say Anything.
Because of its listening brief, NSA has been heavily involved in cryptanalyticCryptanalysis (from the Greek kryptos and analyein "to loosen" or "to untie") is the study of methods for obtaining the meaning of encrypted information without access to the secret information which is normally required to do so. Typically, this involves research, continuing the work of its predecessor agencies which had been responsible for breaking many World War IIWorld War II was the most extensive and costly armed conflict in the history of the world, involving the great majority of the world's nations, being fought simultaneously in several major theatres, and costing tens of millions of lives. The war was fough codeIn the context of cryptography, a code is a method used to transform a message into an obscured form, preventing those not in on the secret from understanding what is actually transmitted. The usual method is to use a codebook with a list of common phrases and cyphers (see, for instance, Purple code, Venona, and JN-25JN-25 is the name used by Western cryptography organizations for the main secure command and control communications scheme used by the Imperial Japanese Navy (JIN) during and before WWII (it was the 25th Japanese Navy system identified). It was an encyphe).
Headquarters for the National Security Agency is at Fort George G. Meade, Maryland, approximately ten miles northeast of Washington, DC. NSA has its own exit off of the Baltimore-Washington Parkway, labelled "NSA Employees Only". The scale of the operations at the NSA is hard to determine from unclassified data, but one clue is the electricity usage of NSA's headquarters. NSA's budget for electricity exceeds $21 million per year, making it the second largest electricity consumer in the entire state of Maryland. Photos have shown there are about 18000 parking spaces at the site, although most guesses have put the NSA's workforce at around double that number.
Its secure government communications brief has involved NSA in production of communications hardware and software, in the production of semiconductors (there is a chip fabrication plant at Ft Meade), in cryptography research, and contracting with private industry for items, equipment, and research it is not itself prepared to develop or supply. Again, this continues responsibilities inherited from its predecessors (see SIGABA).
NSA has been involved in debates about public policy, both as a behind-the-scenes advisor to other departments, and directly during and after Vice Admiral Bobby Ray Inman's directorship.
NSA recommended changes to IBM's submission during the process which produced the DES encryption algorithm in 1976. Subsequently, there were suspicions that those changes were made so as to make it easier for NSA to break the cypher when it so desired; thus carrying out one of its briefs. However, the public reinvention of differential cryptanalysis showed that one of the changes (to the S-boxes) had actually likely been suggested to harden the algorithm against this -- then publicly unknown -- cryptanalytic technique. It remained publicly unknown until Eli Biham and Adi Shamir independently reinvented it and published some decades later. However, the shortening of the 128-bit key used by the IBM submission to a nominal 64, but actually an effective 56, bits has never been explainable as anything other than a weakening of the algorithm, making possible an exhaustive search for the key by those with sufficient computer power and funding. Possibly because of previous controversy, the involvement of NSA in the selection of a successor to DES, the Advanced Encryption Standard (AES) was limited to hardware performance testing (see AES competition).
NSA was a major player in the debates of the mid to late 1990s regarding US munitions export regulations. Cryptographic software and hardware had long been classed with fighter planes, tanks, cannons, and atomic bombs as controllable munitions.
The NSA has, at times, attempted to restrict the publication of academic research into cryptography; for example, the Khufu and Khafre block ciphers.
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