Understanding Vignere Cipher
Vignere Cipher includes a twist with Caesar Cipher algorithm used for encryption and decryption. Vignere Cipher works similar to Caesar Cipher algorithm with only one major distinction: Caesar Cipher includes algorithm for one-character shift, whereas Vignere Cipher includes key with multiple alphabets shift.
For encryption the mathematical equation is as follows −
For decryption the mathematical equation is as follows −
Vignere cipher uses more than one set of substitutions, and hence it is also referred as polyalphabetic cipher. Vignere Cipher will use a letter key instead of a numeric key representation: Letter A will be used for key 0, letter B for key 1 and so on. Numbers of the letters before and after encryption process is shown below −
The possible combination of number of possible keys based on Vignere key length is given as follows, which gives the result of how secure is Vignere Cipher Algorithm −
The tableau used for Vignere cipher is as shown below −