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Classical Ciphers
Caesar Cipher

Caesar Cipher

Encrypt and decrypt text with the Caesar cipher online using custom shift values and multiple alphabets. One of the oldest and most widely known classical encryption methods.

Input
0 chars · 0 bytes
Try:
Result
✓ Letter-shift substitution cipher ✓ Multiple alphabets supported ✓ We never store your messages ✓ Processed on our server
Examples
Encrypt with shift 3 Shift: 3
Input HELLO WORLD
Output KHOOR ZRUOG

Alphabet: English. Shift: 3. Mode: encrypt. Each letter is moved three positions forward.

Decrypt with shift 3 Shift: 3
Input KHOOR ZRUOG
Output HELLO WORLD

Alphabet: English. Shift: 3. Mode: decrypt. The same shift is applied in reverse to restore the original text.

ROT13 example Shift: 13
Input HELLO
Output URYYB

Alphabet: English. Shift: 13. ROT13 is a special Caesar cipher variant commonly used to obscure text.

Preserve spaces and punctuation Shift: 5
Input HELLO, WORLD!
Output MJQQT, BTWQI!

Only letters are shifted. Spaces, punctuation marks, and other symbols remain unchanged.

How the Caesar cipher works

The Caesar cipher is a substitution cipher that shifts each letter in the selected alphabet by a fixed number of positions. For example, with a shift of 3, A becomes D, B becomes E, and C becomes F.

Encryption moves letters forward through the alphabet, while decryption moves them backward by the same shift value. Spaces, numbers, and punctuation are usually preserved unchanged.

Because the method is simple and predictable, it is often used to introduce the basic ideas of classical cryptography: plaintext, ciphertext, keys, encryption, and decryption.

Security and practical limits

The Caesar cipher is not considered secure by modern standards. Since only a small number of shift values are possible, an attacker can test every option very quickly.

Despite its weakness, the cipher remains useful for education, puzzles, and demonstrations because it clearly shows how a secret key changes readable text into ciphertext.

If you need to recover an unknown shift automatically, use Caesar Cracker for key search and analysis.

History of the Caesar cipher

The Caesar cipher is named after Julius Caesar, who is traditionally associated with using letter-shift encryption to protect military messages.

Although the method is extremely weak today, it remains one of the most recognizable historical ciphers and an important starting point for learning how substitution ciphers work.

FAQ

No. The Caesar cipher can be brute-forced quickly because there are only a limited number of possible shifts. It is best used for learning, puzzles, and simple demonstrations.

Yes. Choose the matching alphabet in settings before processing text.

Spaces, digits, and special characters are not changed. Only letters from the selected alphabet are encrypted.

The cipher is named after Julius Caesar, who is traditionally said to have used a letter-shift method to protect military communication.

Live Mode automatically recalculates the result when you change the text or encryption settings. This lets you see the result instantly without pressing the button.

This mini-app is designed for encryption and decryption when you already know the shift. For automatic key search and frequency-based analysis, use Caesar Cracker.
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