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Vigenère Cipher Encoder & Decoder

The Vigenère Cipher is a method of encrypting alphabetic text by using a series of interwoven Caesar ciphers, based on the letters of a keyword. It is a form of polyalphabetic substitution. First described by Giovan Battista Bellaso in 1553, the cipher is easy to understand and implement, but for three centuries it resisted all attempts to break it; this earned it the description 'le chiffre indéchiffrable' (the indecipherable cipher). It offers significantly higher complexity than monoalphabetic ciphers like Caesar.

Cipher

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Cipher Settings

Secret word for determining the shift for each letter

💡 Tip: Longer keywords with varied letters provide better encryption

Processed Text

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Cipher Settings

Vigenère Cipher

Uses a keyword to determine the shift for each letter

Keyword Requirements:

  • Any word or phrase (only letters A-Z are used)
  • Minimum 6 characters recommended
  • Examples: "SECRET", "PASSWORD", "KEY2024", "CRYPTO"
  • Longer keywords provide better security

Who Uses This Tool

  • • Cryptography students studying polyalphabetic substitution
  • • Puzzle designers creating hard-to-crack text riddles
  • • History buffs recreating Renaissance-era secret messages
  • • Education professionals demonstrating key-based encryption
  • • Developers implementing basic obfuscation with keys

Key Features

  • ✓ Key-based encryption (Polyalphabetic)
  • ✓ Resistant to simple frequency analysis
  • ✓ Preserves message structure (length and spacing)
  • ✓ Supports mixed-case keys
  • ✓ Client-side secure processing
  • ✓ Interactive encryption/decryption toggle

Frequently Asked Questions

Why was Vigenère called 'the indecipherable cipher'?

Because it uses multiple different alphabets (shifts) toggled by a keyword, it flattens the letter frequency distribution. The standard method to break it (Kasiski examination) wasn't published until 1863, over 300 years after the cipher's invention.

How does the 'Key' work?

The key is repeated until it matches the length of the message. If the message is 'HELLO' and key is 'ABC', the key sequence becomes 'ABCAB'. Each letter of the key determines the Caesar shift amount for the corresponding message letter.

Is it secure for modern banking?

No. While stronger than Caesar, computers can break Vigenère requires trivial effort using frequency analysis of repeated patterns. Modern security uses algorithms like AES (found in HTTPS), which are mathematically complex and key-based.

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