Description
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. 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. Only those letters which occur in the English alphabet are affected; numbers, symbols, whitespace, and all other characters are left unchanged. Because there are 26 letters in the English alphabet and 26 = 2 × 13, the ROT13 function is its own inverse:
- for any basic Latin-alphabet text x.
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).
The transformation can be done using a lookup table, such as the following:
| ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz |
| NOPQRSTUVWXYZABCDEFGHIJKLMnopqrstuvwxyzabcdefghijklm |
For example, in the following joke, the punchline has been obscured by ROT13:
How can you tell an extrovert from an introvert at NSA? Va gur ryringbef, gur rkgebireg ybbxf ng gur BGURE thl'f fubrf.Transforming the entire text via ROT13 form, the answer to the joke is revealed:
Ubj pna lbh gryy na rkgebireg sebz na vagebireg ng AFN? In the elevators, the extrovert looks at the OTHER guy's shoes.A second application of ROT13 would restore the original.
Read more about this topic: ROT13
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