🔒 Caesar Cipher

The Caesar cipher is one of the simplest and most famous classical ciphers. Each letter in the plaintext is shifted by a fixed number of positions in the alphabet. Choose a shift value below, type or paste your text, and click Encrypt or Decrypt. You can also run a brute-force attack when you do not know the key.

Input text

Shift (1–25)

Mode

Output

🔍 Brute-force Decryption

Try all 25 possible shifts at once. The result most likely to be English is highlighted automatically.

How it works: Each letter in the input is shifted by N positions forward (encrypt) or backward (decrypt) in the alphabet, wrapping Z back to A. For example, with shift 3, A→D, B→E, … X→A, Y→B, Z→C.

Note: Only English letters A–Z and a–z are shifted. Numbers, punctuation, and other characters pass through unchanged.

❓ Frequently Asked Questions

A Caesar cipher (named after Julius Caesar) is one of the oldest known substitution ciphers. It works by replacing each letter in the plaintext with a letter a fixed number of positions down the alphabet. With a shift of 3 (Caesar’s original choice), the word HELLO becomes KHOOR. The same idea underpins the more general ROT-N family of ciphers used in puzzles and games.

ROT13 is a Caesar cipher with a shift of exactly 13. Because the Latin alphabet has 26 letters, applying ROT13 twice returns the original text — so the same operation both encrypts and decrypts. ROT13 is widely used on Usenet and online forums to hide spoilers or punchlines from casual readers.

The Caesar cipher has only 25 possible keys (shifts 1–25). Brute-forcing means trying every shift and scoring the output by how many common English words it contains. The shift producing the highest score is almost certainly the original key. This tool highlights the most likely candidate automatically.

No. It is a toy cipher by modern standards — trivially broken by either brute force (25 keys total) or frequency analysis (English has predictable letter frequencies). For real confidentiality, use modern authenticated encryption such as AES-GCM or ChaCha20-Poly1305. The Caesar cipher is great for puzzles, learning, and obfuscation, not for secrets.