World 1 · Substitution · 5 minROT13: the shift that undoes itself
Half the alphabet, twice
Teaching this? Open projector mode
ROT13 is a Caesar shift fixed at 13. The alphabet has 26 letters, so shifting by 13 twice lands you back where you started: encrypting and decrypting are the same operation.
Online forums used it to hide spoilers and joke punchlines. It hides text from a casual glance, not from anyone who wants to read it.
Check yourself
Why does applying ROT13 twice give back the original text?
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