Decrypting Text - code breaking software
The Colossus at Bletchley

Affine cipher decryption

Many ciphers are automated and rely on a mathematical encryption algorithm. One common class of letter shift ciphers is known as the affine shift cipher. It uses the form x -> 3x + 5 where the numbers can vary. The aim is that by knowing the letter substitutions for 2 letters then we can solve the 2 simultaneous equations. However, this means division in modulus maths - which may not be possible if a multiplicative inverse cannot be found. So you may need to try a few characters before this works.

 

The box below contains example encrypted text. You can paste the text that you want to decipher over this example text. Then fill in your replacement letters.
Enter your ciphertext below
Enter your replacement letters in the boxes below:
  1 2
encrypted
DECRYPTED?