 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 . ROT13 is a special case of the Caesar cipher , developed in ancient Rome . Because there are 26 letters ( 2 × 13 ) in the basic Latin alphabet , the Caesar cipher is a 26-letter cipher , and ROT13 is a 26-letter cipher . ROT13 is also a special case of the XOR cipher , which uses the exclusive-or ( XOR ) operation .
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