Learn cryptography hands-on: classical ciphers + real AES-256-GCM — 100% in your browser
Caesar Cipher ~100 BC
Every letter is shifted by a fixed number of places in the alphabet. ROT13 is simply Caesar with a shift of 13 — because 13 is half of 26, the same operation encrypts and decrypts.
Vigenère Cipher 1553
A keyword repeats over the message; each letter is shifted by the matching keyword letter. It resisted casual codebreaking for 300 years — until frequency analysis with the Kasiski examination defeated it.
AES-256-GCM MODERN STANDARD
This is real encryption — the same algorithm used by HTTPS, VPNs and encrypted messengers. Your password is stretched with PBKDF2 (150,000 iterations, random salt) into a 256-bit key, and every encryption uses a fresh random IV. Output format: salt : iv : ciphertext in Base64. Nothing leaves your device.
✅ Try it: encrypt a message, copy the token, then decrypt it with the same password. A wrong password fails completely — GCM authentication detects any tampering, so you get an error instead of garbage.
Why Classical Ciphers Are Not Secure
The classical ciphers above are wonderful teaching tools — and completely unsafe for real secrets. Here is why:
Tiny key space. Caesar has only 25 possible keys. A computer tries all of them in microseconds (tap “Show all 25 shifts” above). Real security needs a key space so large that trying every key is physically impossible — AES-256 has 2²⁵⁶ keys.
Letter patterns leak. In English, “E” is the most common letter. Under Caesar or Vigenère, the most common ciphertext letter maps straight back to it — this is frequency analysis, known since the 9th century.
Structure survives encryption. Word lengths, repeated words and punctuation stay visible. Modern ciphers destroy all visible structure.
No integrity. Classical ciphers cannot detect tampering. AES-GCM is authenticated encryption: change one bit and decryption fails loudly.
Kerckhoffs's principle. Real systems stay secure even when the algorithm is public — only the key is secret. Classical ciphers often relied on hiding the method itself.
⚠️ Never protect real data with Caesar, ROT13 or Vigenère. ROT13 is fine for hiding spoilers in forums — it is an encoding convention, not security. For real secrets use AES-GCM, ChaCha20-Poly1305, or a trusted encrypted app.
Learn next: hashing vs encryption (they are different!), public-key cryptography (RSA, Diffie–Hellman), and why password storage uses slow salted hashes like bcrypt or Argon2.
Privacy & Ethics
Everything runs locally in your browser — no message, password or ciphertext is ever uploaded. This playground is an educational tool for learning how cryptography works and why modern standards replaced classical ciphers. Use encryption knowledge to protect your own data and communications.