Caesar Cipher Explained
The Caesar cipher shifts every letter by a fixed number of positions in the alphabet. It is the classic introduction to substitution and modular arithmetic. Use Cipher Portal to encrypt or decrypt, or open the Caesar cipher decoder for a decrypt-focused walkthrough.
What is a Caesar cipher?
Also called a shift cipher, Caesar encryption adds the same integer (0–25) to every letter modulo 26. A shift of 3 maps A→D, B→E, and Z→C with wraparound. Decryption subtracts the same shift. The cipher is monoalphabetic: one displaced frequency profile survives, which is why statistical attacks work.
Historians associate the name with Julius Caesar, who reportedly used a shift of three for military notes. Modern puzzles, geocaching legs, and first-year security courses still use Caesar because the math is transparent and brute force needs only 26 trials.
How Caesar encryption works
Treat A as 0 through Z as 25. Encryption computes (index + shift) mod 26 for each letter; non-letters are usually left unchanged. The key is a single integer—Cipher Portal accepts 0–25 in the key field when Caesar is selected.
Because every letter moves by the same offset, English letter frequencies stay recognizable: the histogram is only slid along the alphabet. That property makes Caesar a teaching contrast for Vigenère (changing shifts) and Enigma (rotor stepping).
Security and classroom limits
An attacker tries all 26 shifts and ranks outputs against English models—exactly what the Frequency Analysis Lab demonstrates. Short messages may score ambiguously, but homework-length ciphertext rarely survives.
Caesar teaches keys, inverses, and brute force; it does not provide confidentiality against anyone with a computer. To decrypt without the shift, follow the Caesar cipher cracker guide or decrypt without a key overview. Pair this hub with Caesar cipher examples you can verify line by line.
Frequently asked questions
What is a Caesar cipher?
A monoalphabetic substitution that shifts every letter by the same fixed amount modulo 26.
What is a shift cipher decoder?
A tool that decrypts Caesar ciphertext when you know the shift, or tries all 26 shifts to recover the key.
Is Caesar the same as ROT13?
ROT13 is Caesar with shift 13; applying it twice returns the original text.
How do I encrypt online?
Open Cipher Portal, select Caesar, enter text and shift, then run encrypt or decrypt.
Try the Caesar cipher online — encrypt, decrypt, or run key recovery.