Editing ROT13 (section)

==Description==
Applying ROT13 to a piece of text requires examining its alphabetic characters and replacing each one by the letter 13 places further along in the [[alphabet]], wrapping back to the beginning as necessary.<ref name="schneier">{{Cite book|last=Schneier |first=Bruce |author-link= Bruce Schneier |title=Applied Cryptography |url=https://archive.org/details/appliedcryptogra00schn_605 |url-access=limited |edition=Second|year=1996|publisher=John Wiley & Sons |isbn= 0-471-11709-9|pages=[https://archive.org/details/appliedcryptogra00schn_605/page/n198 11] }}</ref>

When encoding a message, <kbd>A</kbd> becomes <kbd>N</kbd>, <kbd>B</kbd> becomes <kbd>O</kbd>, and so on up to <kbd>M</kbd>, which becomes <kbd>Z</kbd>. Then the sequence continues at the beginning of the alphabet: <kbd>N</kbd> becomes <kbd>A</kbd>, <kbd>O</kbd> becomes <kbd>B</kbd>, and so on to <kbd>Z</kbd>, which becomes <kbd>M</kbd>. When decoding a message, the same substitution rules are applied, but this time on the ROT13 encrypted text. Other characters, such as numbers, symbols, punctuation or [[Whitespace character|whitespace]], are left unchanged.

Because there are 26 letters in the [[Latin alphabet]] and 26 = 2 &times; 13, the ROT13 function is its own [[inverse function|inverse]]:<ref name="schneier" />

:<math>\mbox{ROT}_{13}(\mbox{ROT}_{13}(x))=x</math> for any basic Latin-alphabet text <math>x</math>.

In other words, two successive applications of ROT13 restore the original text (in [[mathematics]], this is sometimes called an ''[[involution (mathematics)|involution]]''; in cryptography, a ''[[reciprocal cipher]]'').

The transformation can be done using a [[lookup table]], such as the following:
{| class="wikitable"
| Input
| <kbd><span style="color: light-dark(darkred, pink)">ABCDEFGHIJKLM</span><span style="color: light-dark(darkblue, lightblue)">NOPQRSTUVWXYZ</span><span style="color: light-dark(darkred, pink)">abcdefghijklm</span><span style="color: light-dark(darkblue, lightblue)">nopqrstuvwxyz</span></kbd>
|-
| Output
| <kbd><span style="color: light-dark(darkblue, lightblue)">NOPQRSTUVWXYZ</span><span style="color: light-dark(darkred, pink)">ABCDEFGHIJKLM</span><span style="color: light-dark(darkblue, lightblue)">nopqrstuvwxyz</span><span style="color: light-dark(darkred, pink)">abcdefghijklm</span></kbd>
|}

For example, in the following joke, the punchline has been obscured by ROT13:
: Why did the chicken cross the road?
:Gb trg gb gur bgure fvqr!

Transforming the entire text via ROT13 form, the answer to the joke is revealed:
: Jul qvq gur puvpxra pebff gur ebnq?
: To get to the other side!

A second application of ROT13 would restore the original.