Generates the key \( k \)
Encrypts the message \( m \):
Enter a message (a sentence containing only whitespace and the letters A-Z) that Alice wants to send encrypted to Bob:
Use the following key (a word shorter than the message which only contains the letters A-Z):
Hit enter to generate the parameters and use the left and right arrow keys to navigate.
Alice generates the key \( k \) of the keyword \( kw \) where \( k \) must have the same length as the message \( m \). If the keyword is shorter than the message, the keyword is repeated until its length is equal to the length of the message.
She then sends the key \( k \) through a secure channel to Bob.
Before Alice can encrypt the message \( m \) she needs the index in the English alphabet of each letter in the message \( m \) with the letter \( a \) starting at index \( 0 \).
Alice then use the key \( K \) to encrypt the message \( m \).
Before Bob can decrypt the ciphertext \( c \) he needs the index in the English alphabet of each letter in the ciphertext \( c \) with the letter \( a \) starting at index \( 0 \).
Decryption is almost identical to encryption: Instead of adding the two numbers we subtract them.
Receives the key \( k \)
Receives the ciphertext \( c \)
Decrypts the ciphertext \( c \):