![]() It is used to hide potentially offensive jokes, or to obscure an answer to a puzzle or other spoiler. ROT13 was in use in the net.jokes newsgroup by the early 1980s. The extrovert looks at the OTHER guy's shoes.Ī second application of ROT13 would restore the original. Transforming the entire text via ROT13 form, the answer to the joke is revealed: Gur rkgebireg ybbxf ng gur BGURE thl'f fubrf. NOPQRSTUVWXYZABCDEFGHIJKLMnopqrstuvwxyzabcdefghijklmįor example, in the following joke, the punchline has been obscured by ROT13: The transformation can be done using a lookup table, such as the following: ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz In other words, two successive applications of ROT13 restore the original text (in mathematics, this is sometimes called an involution in cryptography, a reciprocal cipher). Because there are 26 letters in the English alphabet and 26 = 2 × 13, the ROT13 function is its own inverse: for any basic Latin-alphabet text x. Only those letters which occur in the English alphabet are affected numbers, symbols, whitespace, and all other characters are left unchanged. A becomes N, B becomes O, and so on up to M, which becomes Z, then the sequence continues at the beginning of the alphabet: N becomes A, O becomes B, and so on to Z, which becomes M. Īpplying ROT13 to a piece of text merely requires examining its alphabetic characters and replacing each one by the letter 13 places further along in the alphabet, wrapping back to the beginning if necessary. ROT13 has been described as the " Usenet equivalent of a magazine printing the answer to a quiz upside down". ROT13 is used in online forums as a means of hiding spoilers, punchlines, puzzle solutions, and offensive materials from the casual glance. ROT13 has inspired a variety of letter and word games on-line, and is frequently mentioned in newsgroup conversations. The algorithm provides no cryptographic security, and is often cited as a canonical example of weak encryption. In the basic Latin alphabet, ROT13 is its own inverse that is, to undo ROT13, the same algorithm is applied, so the same action can be used for encoding and decoding. ROT13 is an example of the Caesar cipher, developed in ancient Rome. ROT13 (" rotate by 13 places", sometimes hyphenated ROT-13) is a simple letter substitution cipher that replaces a letter with the letter 13 letters after it in the alphabet. For example, HELLO becomes URYYB (or, reversing, URYYB becomes HELLO again). There is a site that list many hundreds of implementations of this example (but please don't copy content from them).ROT13 replaces each letter by its partner 13 characters further along the alphabet. This category's articles describe programs that perform the Rot13 cypher. It also has the interesting property of symmetry: the encrypted text can be passed though the same process to return the plain text. But it is a nice example that can serve as a introductory example for most programming languages. Like all substitution cyphers, it is easy to break (even easier if you know or can guess that it's been used). It is similar in operation to the base-64 algorithm used to hide user names and passwords from the casual observer in the HTTP basic authentication scheme. For example it is used in some email or online forums to hide punchlines to jokes or answers to quizzes. Rot13 is a simple substitution cypher that is used as a simple, but easy to break, obfuscation technique.
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