Affine Cipher
Encrypt and decrypt text using the Affine cipher, locally in your browser.
🔒 Your data is processed locally in your browser and is never uploaded to our servers.
How it works
The Affine cipher transforms each letter using the formula E(x) = (ax + b) mod 26. For decryption, the modular inverse of a is used. Only letters are transformed; spaces, numbers and punctuation remain unchanged.
Examples
With a = 5 and b = 8:
HELLO → RCLLA
Security notes
The Affine cipher is a classical substitution cipher and is not considered secure for protecting sensitive information.
FAQ
What values can I use for a?
The value of a must be relatively prime to 26. Valid values are 1, 3, 5, 7, 9, 11, 15, 17, 19, 21, 23 and 25.
What is b?
b is the additive shift applied after multiplying the letter value by a.
Are spaces and punctuation changed?
No. Only letters from A-Z and a-z are transformed.