![]() Even without this knowledge, the algorithm is easily broken through frequency analysis. ![]() ROT13 is not intended to be used where secrecy is of any concern-the use of a constant shift means that the encryption effectively has no key, and decryption requires no more knowledge than the fact that ROT13 is in use. ROT13 is equivalent to an encryption algorithm known as a Caesar cipher, attributed to Julius Caesar in the 1st century BC. Email addresses also sometimes encoded with ROT13 to hide them from less sophisticated spam bots. ROT13 is typically supported as a built-in feature to newsreading software. A shift of thirteen was chosen over other values, such as three as in the original Caesar cipher, because thirteen is the value which arranges that encoding and decoding are equivalent, thereby allowing the convenience of a single command for both. 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: ROT 13(ROT 13( x)) = ROT 26( x) = x for any 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 reverses: N becomes A, O becomes B, and so on to Z, which becomes M. ROT13 has inspired a variety of letter and word games on-line, and is frequently mentioned in newsgroup conversations.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. It is often cited as a canonical example of weak encryption. The algorithm provides no real cryptographic security and should never be used for such. 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 a variation of the Caesar cipher, developed in ancient Rome. ROT13 has been described as the " Usenet equivalent of a magazine printing the answer to a quiz upside down". ROT13 (" rotate by 13 places", sometimes hyphenated ROT-13) is a simple substitution cipher used in online forums as a means of hiding spoilers, punchlines, puzzle solutions, and offensive materials from the casual glance. For example, HELLO becomes URYYB (or, decrypting, URYYB becomes HELLO again). ROT13 replaces each letter by its partner 13 characters further along the alphabet.
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