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Substitution Cipher

Encrypt or decrypt text with a fully custom monoalphabetic substitution alphabet.

Learn how substitution ciphers work

Input Text

Letters: 0
Total chars: 0

Output Text

Status: Valid
Output chars: 0

Cipher Properties

Type: Monoalphabetic Key: Permutation Decrypt: Reverse Mapping Weakness: Frequency Analysis Active Mode: Encrypt
Using This Tool: Guide & Notes Show guide

The Substitution Cipher tool lets you define the complete plain alphabet and cipher alphabet for a monoalphabetic substitution.

How to use it

  • Choose Encrypt or Decrypt.
  • Use the default alphabets, type your own 26-letter alphabets, generate a random alphabet, or build one from a keyword.
  • Paste text into the input box and read the output as the mapping updates.
  • Use the mapping table to confirm which plaintext letters currently map to which cipher letters.

Options and settings

  • Plain Alphabet and Cipher Alphabet must each contain A-Z exactly once.
  • Keyword Builder creates a cipher alphabet from unique keyword letters followed by unused letters.
  • Atbash Style reverses the alphabet as a quick preset.
  • Group letters creates classical uppercase blocks and ignores punctuation, numbers, and whitespace.

Notes

  • This is a monoalphabetic substitution cipher, so each letter always maps to one replacement letter.
  • It is useful for puzzles and learning, but it is vulnerable to frequency analysis.
See all tools
Keyword Cipher Build a keyed substitution alphabet from a cleaned keyword. Pigpen Cipher Turn letters into the geometric grid-and-X symbols of the Pigpen cipher, or decode a message with the clickable visual alphabet. Vigenère Cipher Polyalphabetic substitution cipher using a repeating key. Beaufort Cipher Use a repeating keyword with the reciprocal Beaufort rule C = K - P mod 26.
Related Article

Simple Substitution Cipher: Every Letter Wears a Mask

How a scrambled alphabet became the simplest general form of classical substitution, and why the patterns of language still give it away.

Read the article
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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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