03 What is ROT-13?

With ROT-13 letters are shifted by 13 digits.

A⇄N
B⇄O
C⇄P
D⇄Q
E⇄R
F⇄S
G⇄T
H⇄U
I⇄V
J⇄W
K⇄X
L⇄Y
M⇄Z