04-10: Caesar Cipher¶

Home | All Projects | Notes | Exercises | Quiz Hub

Encrypts and decrypts messages using the Caesar cipher (letter-shifting). Also includes a brute-force mode that prints all 25 possible decryptions when the shift is unknown.

Topics covered: ord() / chr() · modular arithmetic · str.isalpha() · str.islower() · functions · for loop · while-loop menu

Difficulty: ⭐ Beginner

How to Run¶

python main.py

Sample Output¶

Encrypted (shift 3):
  Khoor, Zruog!

Brute-force (shift 3 found at row 3):
  Shift    Decrypted text
  1        Jgnnq, Yqtnf!
  2        Ifmmp, Xpsme!
  3        Hello, World!   ← readable!
  ...

Key Concepts Practised¶

Concept	Where used
`ord(char) - ord('a')`	Convert letter → 0-based index
`% ALPHABET_SIZE`	Wrap-around (Z+1 → A)
`chr(base + shifted)`	Convert index back → letter
Preserving case	Choosing `ord('a')` vs `ord('A')` as base
Non-letter pass-through	`if char.isalpha()` guard