ROT13 ("ROTate by 13 places", sometimes hyphenated ROT-13, sometimes 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" [1].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.
1 Description
To apply ROT13 to a piece of text, take every letter in the Latin alphabetThe Latin alphabet also called the Roman alphabet is the most widely used alphabetic writing system in the world, the standard script of the English language and most of the languages of western and central Europe, and of those areas settled by Europeans. and replace it by the letter 13 places further along in the alphabet, wrapping back to the beginning if necessary, preserving case: a becomes n, B becomes O, and so forth, down to Z, which becomes M. Numbers, symbols, and other characters are left unchanged. Because there are 26 letters in the Latin alphabet and 26 = 2 × 13, the ROT13 function is its own inverseIn mathematical analysis, an inverse function is in simple terms a function which "does the reverse" of a given function. More formally, if f is a function with domain X, then f -1 is its inverse function if and only if for every we have: :. For example,:
- for any text x.
In other words, two successive applications of ROT13 restore the original text (in mathematicsMathematics is commonly defined as the study of patterns of structure, change, and space; more informally, one might say it is the study of "figures and numbers". In the formalist view, it is the investigation of axiomatically defined abstract structures, this is sometimes called an involutionAbstract algebra In mathematics, an involution is a function that is its own inverse, so that f ''f ''x ) x for all x in the domain of f''. The identity map provides a trivial example of an involution. Common examples in mathematics of more interesting in).
The transformation can be done using a lookup tableIn computer science, a lookup table is a data structure, usually an array or associative array, used to replace a runtime computation with a simpler lookup operation. The speed gain can be significant, since retrieving a value from memory is often faster, such as the following:
| abcdefghijklmnopqrstuvwxyz
|
| NOPQRSTUVWXYZABCDEFGHIJKLM
|
For example, someone might wish to obscure the following text:
How can you tell an extrovert from an
introvert at NSAThis article is about the NSA government agency. For other uses, see NSA (disambiguation). The National Security Agency (NSA is a United States government agency responsible for both the collection and analysis of message communications, and for the secur? In the elevators,
the extroverts look at the OTHER guy's shoes.
Transformed into ROT13 form, the text would become:
Ubj pna lbh gryy na rkgebireg sebz na
vagebireg ng AFN? Va gur ryringbef,
gur rkgebiregf ybbx ng gur BGURE thl'f fubrf.
A second application of ROT13 would restore the original.
