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ROT13 is a system for obscuring text typically used in online forums as a means of hiding joke punchlines, movie and story spoilers, and offensive expressions from the casual glance.

The name "ROT13" stands for "rotate by 13 places", which is a concise description of the algorithm. To apply ROT13 to a piece of text, take every letter which is in the Roman alphabet and shift it by 13 places down the alphabet, wrapping back to the beginning if necessary: 'A' becomes 'N', 'B' becomes 'O', and so forth, down to 'Z' becoming 'M'. Numbers, symbols, and other characters are not changed. Because there are 26 letters in the Roman alphabet and 26 = 2 × 13, the ROT13 function is its own inverse: x = ROT13(ROT13(x)) for any text x; this is sometimes called an involution.

ROT13 is a type of historical encryption algorithm known as a Caesar cipher, though it is not intended to be ensure secrecy. Instead, it requires the viewer of a message to consciously choose to decipher it, which typically means invoking a ROT13 command in software. Rather than protecting the encrypted message from unauthorized readers, ROT13 protects readers from material they may not wish to read, such as spoilers in book or movie reviews.

Because of its unsuitability for secrecy, ROT13 has become a catchphrase to refer to any weak encryption, for example: "56-bit DES is no better than ROT13 these days." Worse yet is double ROT13, equivalent to sending the plaintext). Thus the poisonously ironic "Sure, go ahead, it's perfectly safe to send your credit card number in email. Just make sure to encrypt it with double ROT13."

Example

The transformation can be done using a lookup table, such as the following:

abcdefghijklmnopqrstuvwxyz
NOPQRSTUVWXYZABCDEFGHIJKLM

Thus, the message:

"How you can tell an extrovert from an introvert at NSA? In the elevators? The extroverts look at the OTHER guy's shoes."

would be, in ROT13 form:

"Hbj lbh pna gryy na rkgebireg sebz na vagebireg ng AFN? Va gur ryringbef? Tur rkgebiregf ybbx ng gur BGURE thl'f fubrf."

A second application of ROT13 recovers the original.

External links

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-'''ROT13''' is a [[involution|self-reversing]] [[Caesar cipher]] popularly used on [[Usenet]] and other online forums as a means of masking joke punchlines, movie and story [[spoiler (media)|spoiler]]s, and offensive expressions from the casual glance.
+'''ROT13''' is a system for obscuring text typically used in online forums as a means of hiding joke [[punchline]]s, movie and story [[spoiler (media)|spoiler]]s, and offensive expressions from the casual glance.
-The name "ROT13" stands for "rotate by 13 places," which is a concise description of the cipher [[algorithm]]. To apply ROT13 to a piece of text, take every letter which is in the [[Roman alphabet]] and shift it by 13 places down the alphabet, wrapping back to the beginning if necessary: 'A' becomes 'N', 'B' becomes 'O', and so forth, down to 'Z' becoming 'M'. Numbers, symbols, and other characters are not changed. Because there are 26 letters in the [[Roman alphabet]] and 26 = 2 &times; 13, the ROT13 function is its own inverse: ''x'' = ROT13(ROT13(''x'')) for any text ''x''.
+The name "ROT13" stands for "'''rotate by 13 places'''", which is a concise description of the [[algorithm]]. To apply ROT13 to a piece of text, take every letter which is in the [[Roman alphabet]] and shift it by 13 places down the alphabet, wrapping back to the beginning if necessary: 'A' becomes 'N', 'B' becomes 'O', and so forth, down to 'Z' becoming 'M'. Numbers, symbols, and other characters are not changed. Because there are 26 letters in the [[Roman alphabet]] and 26 = 2 &times; 13, the ROT13 function is its own inverse: ''x'' = ROT13(ROT13(''x'')) for any text ''x''; this is sometimes called an ''[[involution]]''.
-ROT13 is not intended to be secure. It is intended merely to require the viewer of a message to consciously choose to decipher it, which generally involves no more than invoking the ROT13 command of one's [[newsreader]] software.  Rather than protecting the encrypted message from unauthorized readers, ROT13 protects readers from material they may not wish to view, such as [[spoiler (media)|spoiler]]s in [[book]] or [[movie]] [[review]]s.
+ROT13 is a type of historical [[encryption algorithm]] known as a [[Caesar cipher]], though it is not intended to be ensure [[confidentiality|secrecy]].  Instead, it requires the viewer of a message to consciously choose to [[decipher]] it, which typically means invoking a ROT13 command in software.  Rather than protecting the encrypted message from unauthorized readers, ROT13 protects readers from material they may not wish to read, such as [[spoiler (media)|spoiler]]s in [[book]] or [[movie]] [[review]]s.
-Because ROT13 is sometimes mistaken for real encryption by those unfamiliar with it, it has become a catchphrase among [[cryptography]] buffs to refer to any badly chosen, poor encryption; for example, "56-bit [[DES]] is no better than ROT13 these days."  Worse yet, naturally, is ''double ROT13'', which is equivalent to sending the [[plaintext]]. Thus the poisonously ironic ''"Sure, go ahead, it's perfectly safe to send your credit card number in email.  Just make sure to encrypt it with double ROT13."''
+Because of its unsuitability for secrecy, ROT13 has become a catchphrase to refer to any weak [[encryption]], for example: "56-bit [[DES]] is no better than ROT13 these days."  Worse yet is ''double ROT13'', equivalent to sending the [[plaintext]]). Thus the poisonously ironic ''"Sure, go ahead, it's perfectly safe to send your credit card number in email.  Just make sure to encrypt it with double ROT13."''
-== ROT13 Table ==
+== Example ==
+The transformation can be done using a [[lookup table]], such as the following:
+ abcdefghijklmnopqrstuvwxyz
- ABCDEFGHIJKLM
+ NOPQRSTUVWXYZABCDEFGHIJKLM
- NOPQRSTUVWXYZ
+Thus, the message:
+ "How you can tell an extrovert from an introvert at [[NSA]]? In the elevators? The extroverts look at the OTHER guy's shoes."
+would be, in ROT13 form:
+ "Hbj lbh pna gryy na rkgebireg sebz na vagebireg ng AFN? Va gur ryringbef? Tur rkgebiregf ybbx ng gur BGURE thl'f fubrf."
+A second application of ROT13 recovers the original.
 ==See also==
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 == External links ==
 * [http://www.pflock.de/rot13.htm ROT13 encoder/decoder] Uses JavaScript
 * [http://www.dantas.com/rot13 Bilingual (Portuguese/English) page with explanations, links and software information ]
 [[de:ROT13]]