What is the Caesar Cipher?
The Caesar cipher is one of the simplest and oldest known encryption techniques. Named after Julius Caesar, who used it to send secret messages, it works by shifting each letter in the plaintext by a fixed number of positions down the alphabet.
Key Features:
- Substitution Cipher: Replaces each letter with another based on a fixed shift.
- Symmetric: Same key (shift value) used for both encryption and decryption.
- Alphabet-Based: Works only on letters; does not change numbers or symbols.
- Historical Importance: Often taught as a basic example of classical encryption.
Common Uses:
- Teaching basic cryptography concepts
- Simple puzzles and games
- Basic encoding in non-critical applications
How the Caesar Cipher Works
To encrypt a message, each letter in the plaintext is shifted a certain number of places down the alphabet. For example, with a shift of 3:
- A → D
- B → E
- HELLO → KHOOR
To decrypt, the process is reversed by shifting in the opposite direction.
The Caesar cipher is a special case of the shift cipher, where the alphabet is rotated. It is not secure by modern standards, but useful for learning.
Security Analysis
Pros:
- Simple and easy to understand
- Good for educational purposes
- Quick to implement
Cons:
- Very insecure — only 25 possible shifts
- Vulnerable to brute-force and frequency analysis attacks
- Only suitable for very simple contexts
Example Shifts
| Shift | Plaintext | Ciphertext |
|---|---|---|
| +1 | HELLO | IFMMP |
| +3 | HELLO | KHOOR |
| +13 | HELLO | URYYB |