Free Online Tool

Affine Cipher

Apply mathematical transformations for encryption using the Affine cipher algorithm.

Affine Cipher

Mathematical substitution cipher

Mode

Input Text

Characters: 0Words: 0

Output Text

Example Texts

Click any example to load it

Hello World

Basic example

The quick brown fox jumps over the lazy dog

Pangram

Testing 123!

Mixed content

How to Use Affine Cipher

Enter plaintext and leave the tool in Encode mode.
The current component applies the fixed defaults a = 5 and b = 8 to every letter.
Switch to Decode and swap the ciphertext back into the input to apply the modular inverse.
Copy the case-preserving result; spaces and punctuation remain unchanged.

For each letter index x, encryption computes (5x + 8) mod 26. Since 5 is coprime to 26, its modular inverse makes decryption possible.

Encode with a = 5, b = 8 — input:

AFFINE CIPHER

Output:

IHHWVC SWFRCP

Case-preserving encode — input:

Hello

Output:

Rclla

All processing happens in your browser. No data is sent to servers.

No registration, no limits, completely free to use.