Modular Math and the Shift Cipher

The Caesar Cipher is a type of shift cipher. Shift Ciphers work by using the
modulo operator to encrypt and decrypt messages. The Shift Cipher has a key K,
which is an integer from 0 to 25. We will only share this key with people
that we want to see our message.

How to Encrypt:

For every letter in the message M :

1. Convert the letter into the number that matches its order in the alphabet starting from 0, and call this number X. ( A = 0, B = 1, C = 2, ...,Y = 24, Z = 25)
2. Calculate: Y = (X + K) mod 26
3. Convert the number Y into a letter that matches its order in the alphabet starting from 0. ( A = 0, B = 1, C = 2, ...,Y = 24, Z = 25)

For Example:

We agree with our friend to use the Shift Cipher with key K = 19 for our message. We encrypt the message caesar, as follows:​ So, after applying the Shift Cipher with key K = 19 our message text caesar gave us cipher text vtxltk. We give the message vtxltk to our friend.

How to decrypt:

For every letter in the cipher text C :

1. Convert the letter into the number that matches its order in the alphabet starting from 0, and call this number Y. ( A = 0, B = 1, C = 2, ...,Y = 24, Z = 25)
2. Calculate: X = (Y - K) mod 26
3. Convert the number X into a letter that matches its order in the alphabet starting from 0. ( A = 0, B = 1, C = 2, ...,Y = 24, Z = 25)

Our friend now decodes the message using our agreed upon key K = 19. As follows: So, after decrypting the Shift Cipher with key K = 19 our friend deciphers the cipher text vtxltk into the message text caesar.

How to use the Cipher Calculator?

type : Select the encryption method you want

Range : Specify the domain you want to encode, whether uppercase or lowercase letters, or both

Just enjoy. 😄