Keyword Cipher

Build a keyed substitution alphabet from a cleaned keyword.

Keyword

The keyed alphabet is built from the cleaned keyword first, then the remaining unused letters A-Z.

Type: Monoalphabetic substitution Normalised keyword: ZEBRAS Unique letters: 6 Keyed alphabet: ZEBRASCDFGHIJKLMNOPQTUVWXY Plain A → Cipher Z Plain B → Cipher E

Options

Preserve case

Keep punctuation & numbers

Remove whitespace

Group letters

Encryption maps plain alphabet A-Z onto the keyed cipher alphabet. Decryption reverses that mapping.

Output status

Mode: Encrypt Effective keyword: ZEBRAS Letters processed: 0 Input chars: 0 Output chars: 0 Blocks: 0

In this tool, the keyword ZEBRAS builds the cipher alphabet ZEBRASCDFGHIJKLMNOPQTUVWXY. So with that keyword, A → Z, B → E, C → B, and so on.

Input text

Output text

Using This Tool: Guide & Notes Show guide

The Keyword cipher builds a substitution alphabet by writing a cleaned keyword first, then adding the unused alphabet letters.

How to use it

Enter a keyword.
Choose Encrypt or Decrypt.
Paste the message into the input box.
Check the generated cipher alphabet before copying the result.

Options and settings

Keyword cleaning removes repeated letters and unsupported characters before building the alphabet.
Preserve case keeps the original letter style in the output.
Keep punctuation and numbers controls whether unsupported characters stay visible.
Grouping creates traditional ciphertext blocks.

Notes

The keyword is not used repeatedly like Vigenere; it only builds the substitution alphabet.
Letter frequencies are still preserved, so long messages are vulnerable to frequency analysis.

Keyword Cipher: When a Word Becomes a Secret Alphabet

How a memorable keyword builds a keyed substitution alphabet, and why the pattern still gives the game away.

Read the article

Signal acquired

A note from the team

We build these tools because we love cryptography, encoding, and making difficult ideas easier to explore. If they've helped you, even a small coffee means the world to the project. Thank you!

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