Keyed Digital Expansion Cipher
The simple expansion cipher can be keyed (used with key) to strengthen the ciphertext.
First is to think of a message and a key. In this example, our message will be NO WORRIES and our key will be DRIVE.
First, do the digital Expansion Cipher for the message.
NO WORRIES becomes 77 132 176 141 97 108 45 32 181.
Next, find the Alphanumeric value of the keyword.
DRIVE= 4 18 9 22 5.
Finally, you have to write out the values of the keyword underneath each of the numbers of the message repeatedly and do carrying addition.
.. 77 132 176 141 97 108 45 32 181
+ 4 18 9 22 5 4 18 9 22
= 81 150 185 163 102 112 63 41 203
Final ciphertext is:
81 150 185 163 102 112 63 41 203
~~~CTTRO
