Before computers, secrets were kept by shifting letters. Encode a message with the Caesar and Vigenère ciphers and see why one is trivial and the other held for centuries.
Classical CiphersLive
Caesar & Vigenère
plaintext
ATTACK AT DAWN
↓ encrypt
ciphertext
DWWDFN DW GDZQ
Controls
Presets
The Caesar cipher shifts every letter by a fixed amount — trivially broken by trying all 25 shifts or by letter-frequency analysis. The Vigenère cipher uses a repeating keyword so each letter shifts differently, defeating simple frequency attacks for centuries until the key length could be found. Both are insecure today but perfect for learning how ciphers work.
Reading this result: Every letter shifts by the same 3, so this Caesar cipher's 25-key space is cracked instantly by trying all shifts or by letter-frequency analysis.
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How it works
The Caesar cipher shifts every letter by a fixed amount and falls instantly to frequency analysis. The Vigenère cipher applies a repeating keyword so each letter shifts differently, hiding letter frequencies and resisting attack until the key length can be deduced. Both are obsolete for security today but are the perfect gateway to understanding modern cryptography.
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