![]() ![]() 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. The words "n", "V" (capitalized only), and "gur" (ROT13 for "a", "I", and "the"), and words ending in "yl" ("ly") are examples. In encrypted, normal, English-language text of any significant size, ROT13 is recognizable from some letter/word patterns. By obscuring an email's content, the screening algorithm is unable to identify the email as, for instance, a security risk, and allows it into the recipient's in-box. It is also used to circumvent email screening and spam filtering. Email addresses are 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 for which 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. He used its latinised form, Orffyreus, as his pseudonym. Johann Ernst Elias Bessler, an 18th century clockmaker and constructor of perpetual motion machines, pointed out that ROT13 encodes his surname as Orffyre. ROT13 is a special case of the encryption algorithm known as a Caesar cipher, used by Julius Caesar in the 1st century BC. Jul qvq gur puvpxra pebff gur ebnq? To get to the other side!Ī second application of ROT13 would restore the original. Transforming the entire text via ROT13 form, the answer to the joke is revealed: Why did the chicken cross the road? Gb trg gb gur bgure fvqr! NOPQRSTUVWXYZ ABCDEFGHIJKLM nopqrstuvwxyz abcdefghijklmįor 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:ĪBCDEFGHIJKLM NOPQRSTUVWXYZ abcdefghijklm nopqrstuvwxyz 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 ) ) = x for any basic Latin-alphabet text x. Only those letters which occur in the English alphabet are affected numbers, symbols, punctuation, 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. Applying 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. ![]()
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