Vigenere Cipher

Vigenere encode with keyword KEY.

How it works

• Repeated the keyword across the plaintext letters.
• Shifted each letter by the keyword letter's alphabet position (inverted to decode).

• Non-letters are copied unchanged and do not consume a keyword position.
• The keyword must contain letters only.

Methodology

1. Read the input text one character at a time.
2. Apply the cipher or encoding transformation for the chosen direction.
3. Return the transformed text with a short summary.

Usage

1. Paste or type the text to convert.
2. Choose Encode or Decode.
3. Read the converted text and copy it.

Examples

These are examples, not current values: they use fixed inputs, while the interactive tool computes live results in your browser.

Encode a sample

{
  "text": "HELLO",
  "direction": "encode",
  "key": "KEY"
}

Decode a sample

{
  "text": "RIJVS",
  "direction": "decode",
  "key": "KEY"
}

Limitations

How the Vigenere Cipher works

Encode and decode the Vigenere polyalphabetic cipher with a keyword. The transformation is a single deterministic pass, so the same input always produces the same output.