Encrypt/Decrypt > # Affine cipher - Encoder and decoder

1. Convert each letter in the plain text alphabet to a corresponding integer in the range of 0 to m -1;

2. Calculate the value of each letter as follows (where a and b are the keys of the password):

E(x)=(ax + b) mod m

3. Multiply the integer value of the plain text letter by a, then add b to the result, and finally we take the modulus m (that is, take the remainder when m is removed, or remove the length of the letter until it is less than The length of the number).

For example, let us encrypt the plaintext "AFFINE CIPHER" with the key a = 5, b = 8:

1. First, we must find the integer value of each letter in the plaintext alphabet (take the 26 letters in the alphabet as an example), such as:

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

2) After finding the integer values of the plaintext letters, perform calculations on these values. In this example, the required calculation is (5x + 8);

3) Finally, we must ensure that all answers are calculated in mod 26 and convert the integers back to ciphertext letters.

Finally, the ciphertext obtained is "IHHWVC SWFRCP".