Shows you how to encrypt a word using ROT13 and how to decrypt a ROT13 message. Calculator: https://www.mathcelebrity.com/rot13.php

1. Rot13
● A letter substitution cipher
● Each letter in the alphabet has a numeric position (1 - 26)
○ A = Position 1
○ B = Position 2
○ Z = Position 26
● Replaces each word with the 13th letter after it
● After position (p) greater than 26, letters reset to p - 26
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2. ROT13 Example (Word to Encode)
● MATH
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Original Letter Original Letter
Alphabet Position
Add 13 to the
position
Encoded Letter
M 13 13 + 13 = 26 Z
A 1 1 + 13 = 14 N
T 20 20 + 13 = 33
33 - 26 = 7
G
H 8 8 + 13 = 21 U

3. Rot13 Reverse Translation
● Alphabet position - 13
○ If this value is negative, then subtract the absolute
value of it from 26
○ This is the new position
● Take the alphabet letter from the position
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4. ROT13 Example (Encode to Word)
● ZNGU
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Original Letter Original Letter
Alphabet Position
Subtract 13 from the
position
Encoded Letter
Z 26 26 - 13 = 13 M
N 14 14 - 13 = 1 A
G 7 7 - 13 = -6
26 - abs(-6) = 20
T
U 21 21 - 13 = 8 H

5. ROT13
https://www.mathcelebrity.com/rot13.php
2 options
1. Encrypt a word using ROT13
2. Decrypt a ROT13 word
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