Computer Science / Unit 11 CS 0633 short lesson, about 20 seconds
The Substitution Cipher
Captions available
The idea
A substitution cipher creates ciphertext by substituting plaintext characters, bits, or blocks with alternates — monoalphabetic when each letter maps one way throughout, polyalphabetic when the mapping shifts.
In practice
A puzzle page's cryptogram is the monoalphabetic case, breakable for exactly that reason.
Where people slip
One fixed mapping is one fixed weakness.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
Builds on
Unlocks
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