In an earlier post we discussed a method to encrypt a string using Vigenere Cipher, in this post we see the method to decrypt the encrypted message. The Vigenère cipher is a method of encrypting alphabetic text by using a series of interwoven Caesar ciphers based on the letters of a keyword. It is a form of polyalphabetic substitution . Even though the vigenere cipher is easy to understand and implement, for three centuries it resisted all attempts to break it. In order to encrypt a given message, a table of alphabets can be used, termed a tabula recta , The following is the image of the Table. the above table consists of the alphabet written out 26 times in different rows, each alphabet shifted cyclically to the left compared to the previous alphabet. At different points in the encryption process, the cipher uses a different alphabet from one of the rows. The alphabet used at each point depe...