ROT13 Cipher
Apply ROT13 (rotate by 13) substitution cipher. Since 13 is half of 26, applying ROT13 twice restores the original — it's its own inverse.
About ROT13
ROT13 replaces a letter with the 13th letter after it in the alphabet. A→N, B→O, C→P, ... M→Z, N→A, O→B, ... Z→M. Numbers and symbols are unchanged. It provides no cryptographic security — only mild obfuscation.