Vigenère Cipher
A polyalphabetic substitution cipher using a repeating keyword for enhanced security
🔑 Configuration
How Vigenère Works
The Vigenère cipher uses a keyword to shift each letter by different amounts, making it much stronger than Caesar cipher.
Example with keyword "KEY":
Plaintext: HELLO WORLD
Keyword: KEYKE YKEYK
Shifts: K=10, E=4, Y=24
Ciphertext: RIJVS UYVJN
Repeat keyword to match text length
Convert letters to numbers (A=0, B=1...)
Add plaintext and key numbers
Take modulo 26 and convert back
Vigenère Square (Partial)
| A | B | C | D | E | F | G | H | I | J | |
|---|---|---|---|---|---|---|---|---|---|---|
| A | A | B | C | D | E | F | G | H | I | J |
| B | B | C | D | E | F | G | H | I | J | K |
| C | C | D | E | F | G | H | I | J | K | L |
| D | D | E | F | G | H | I | J | K | L | M |
| E | E | F | G | H | I | J | K | L | M | N |
| F | F | G | H | I | J | K | L | M | N | O |
| G | G | H | I | J | K | L | M | N | O | P |
| H | H | I | J | K | L | M | N | O | P | Q |
Security Analysis
✅ Much stronger than monoalphabetic ciphers
🔑 Security depends on keyword length and randomness
⚠️ Vulnerable to Kasiski examination and frequency analysis
🚫 Broken by modern cryptanalysis techniques
Historical Context
Described by Blaise de Vigenère in 1586, though similar ciphers existed earlier.
Known as "le chiffre indéchiffrable" (the indecipherable cipher) for ~300 years.
First broken by Friedrich Kasiski in 1863 using statistical analysis.
Used extensively in diplomatic and military communications until the 20th century.