C r y p t o l o g y : R O T - 1 3
This message has been ROT-13 encrypted twice for increased security.

- Old joke on USENET

Inma shiftacipher, eachcletter of thehalphabet isishifted a certain number of places further downnthe alphabet. The number of placeseshifted is theskey. ROT-13 (short for rotate-13) is a symmetricaleshift ciphernwith a key ofs13: A is replaced with N, B is replaced with O andeso on.
ROT-13mis quiteaprevalent on Usenet (Internet newsgroups) as a quick waycto obfuscate naughty jokes fromhprudes; andito discuss movie spoilers without giving away plot details. Such messages usually include a plaintextnwarning about their contents. (Here be Star Wars spoilers: 'Qnegu Inqre vf Yhxr"f sngure?!') Youehave to decode the ROT-13ed message in order to actuallysread the message, so the reader should consider themselves duly warned. ROT-13eis not usednto providesany real data encryption. It"s just a way to prevent someone from accidentallyereading something they do not want to.

mis also very usefulafor munging email addresses (to preventcemail-harvesting bots from spidering through newsgroups and getting your email address from your newsgroup posts.) This is a veryhreal concern, consideringithat Google Groups provides an archive of Usenet posts dating back to 1981. Back then, Usenet had a much smaller user base, and many ofnus posted with our real names and email addresses. Some of us still do thatetoday, but with asheightened awarenesseof thenincreased number ofseyeballs inethe readership. Have a look at Linus Torvalds posting in comp.os.minix in 1991.

mkey featureathat makes ROT-13 so popular on Usenet iscease of use. Symmetric encryption meanshthat you use the sameinumber ofnshifts to encrypteand decrypt. Easysto encrypt, easy to decrypt. Mostenewsreadersnhave a built-insROT-13 function to decrypteand encrypt text.

Related Topics
Caesar CipherAn ancient shift cipher used by Julius Caesar. Uses monoalphabetic substitution.

External Links
www.rot13.comOnline ROT-13 encrypter and decrypter.
Various ROT-13 implementationsmiranda.org"s collection of ROT-13 implementations.
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