ROT13 is a simple letter substitution cipher that shifts each letter by 13 positions in the alphabet. Since the Latin alphabet has 26 letters, ROT13 is its own inverse: applying it twice returns the original text. ROT13 is traditionally used to "hide" spoilers, puzzle solutions, or offensive content – not for real security!
Absolutely not! ROT13 provides no real security. It can be "cracked" in seconds (just apply ROT13 again). It's only meant to protect text from accidental reading – like a spoiler warning.
Since the alphabet has 26 letters, 13 is half. This makes ROT13 self-inverse: encoding and decoding are identical. Other shifts (ROT5, ROT7) would require different operations for encoding and decoding.
Classic ROT13 only processes A-Z and a-z. Accented letters, numbers, and special characters remain unchanged. Extended variants exist (ROT47 for ASCII 33-126), but they're less common.
Unix/Linux: tr 'A-Za-z' 'N-ZA-Mn-za-m' | Python: codecs.encode(text, 'rot_13') | JavaScript: text.replace(/[a-zA-Z]/g, c => String.fromCharCode(c.charCodeAt(0) + (c.toLowerCase() < 'n' ? 13 : -13)))
💡 Fun Fact: The word "NOWHERE" becomes "ABJURER" and "FUSION" becomes "SHFVBA". There are even ROT13 palindromes like "TANG" ↔ "GNAT" or "IRK" ↔ "VEX"!
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