Vigenere cipher uses this table together with a keyword to encipher a message. For example, suppose we wish to encipher the plaintext message:
"The secret keyword for today is python"using the keyword "python".
We begin by writing the keyword, repeated as many times as necessary, above the plaintext message. To derive the ciphertext using the tableau, for each letter in the plaintext, one finds the intersection of the row given by the corresponding keyword letter and the column given by the plaintext letter itself to pick out the ciphertext letter.
Encrypt
Keyword: pytho npyth onpyt honpy thonp ython py
Plaintext: These cretk eywor dfort odayi spyth on
Ciphertext: IFXZS PGCMR SLLMK KTBGR HKOLX QIFHU DL
Decipherment of an encrypted message can be done using the Kasiski/Kerckhoff Method.
[Description of the Kasiski method should be placed here...]
Once you determine the keyword, use the vigenere table to decode the ciphet text.
Decrypt
Ciphertext: IFXZS PGCMR SLLMK KTBGR HKOLX QIFHU DL
Keyword: pytho npyth onpyt honpy thonp ython py
Plaintext: These cretk eywor dfort odayi spyth on