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However, in cryptography, code has a more specific meaning: the replacement of a unit of plaintext (i.e., a meaningful word or phrase) with a code word (for example, "wallaby" replaces "attack at dawn"). A cypher, in contrast, is a scheme for changing or substituting an element below such a level (a letter, a syllable, or a pair of letters, etc ...
History of cryptography. Cryptography, the use of codes and ciphers to protect secrets, began thousands of years ago. [ 1] Until recent decades, it has been the story of what might be called classical cryptography — that is, of methods of encryption that use pen and paper, or perhaps simple mechanical aids.
Cryptanalysis (from the Greek kryptós, "hidden", and analýein, "to analyze") refers to the process of analyzing information systems in order to understand hidden aspects of the systems. [ 1] Cryptanalysis is used to breach cryptographic security systems and gain access to the contents of encrypted messages, even if the cryptographic key is ...
Investigations. The following investigations are used in clearance determinations: [ 12] ANACI (Access National Agency Check with Inquiries) – Initial Confidential, Secret, L, LX; only used for civilian employees. NACLC (National Agency Check with Law and Credit) – Initial Confidential, Secret, L, LX; reinvestigations.
An example of a U.S. classified document; page 13 of a United States National Security Agency report [31] on the USS Liberty incident, partially declassified and released to the public in July 2003. The original overall classification of the page, "Top Secret" code word UMBRA, is shown at top and bottom. The classification of individual ...
Encryption. In cryptography, encryption is the process of transforming (more specifically, encoding) information in a way that, ideally, only authorized parties can decode. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Despite its goal, encryption does not ...
NSA encryption systems. The National Security Agency took over responsibility for all U.S. Government encryption systems when it was formed in 1952. The technical details of most NSA-approved systems are still classified, but much more about its early systems have become known and its most modern systems share at least some features with ...
The Government Code and Cypher School (GC&CS) was the first peace-time codebreaking agency, with a public function "to advise as to the security of codes and cyphers used by all Government departments and to assist in their provision", but also with a secret directive to "study the methods of cypher communications used by foreign powers". [11]