ROT13

ROT13 ("ROTate by 13 places", sometimes hyphenated ROT-13, or lowercase rot13) is a simple Caesar cipher used for obscuring text by replacing each letter with the letter thirteen places down the alphabet. A becomes N, B becomes O and so on. The algorithm is used in online forums as a means of hiding joke punchlines, puzzle solutions, movie and story spoilers, and offensive materials from the casual glance. ROT13 has been described as the "Usenet equivalent of a magazine printing the answer to a quiz upside down" http://groups.google.com/groups?selm=UZ36hgCSoh%24%2BEwqG%40nodomain.nodomain.us.

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The name "ROT13" originated on Usenet in the early 1980s, and the method has become a de facto standard. Although a Caesar cipher, a method of encryption thousands of years old, ROT13 provides no real cryptographic security and is not used for such; in fact it is often used as the canonical example of weak encryption. Because ROT13 scrambles only letters, more complex schemes have been proposed to handle numbers and punctuation, or arbitrary binary data.

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Caesar cipher: In cryptography, a Caesar cipher, also known as a Caesar shift cipher or shift cipher, is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions further down the...

Alphabet: An alphabet is a complete standardized set of letters — basic written symbols — each of which roughly represents a phoneme of a spoken language, either as it exists now or as it may have been in the past. There are other systems of writing such as logograms, in which each symbol represe...

Algorithm: In mathematics and computer science an algorithm (the word is derived from the name of the Persian mathematician Al-Khwarizmi) is a finite set of well-defined instructions for accomplishing some task which, given an initial state, will terminate in a corresponding recognizable end-state (contrast wi...