Vigenere cipher

Vigenere cipher

Vigenere cipher is a technique used to substitute alphabetical text using a series of interwoven Caesar cipher based on keyboard letters. It applies the use of a key and a double-entry based on the letters of the keyboard. Vigenere cipher is broken by first mapping the plain texts to numbers that range between 0 to 25 as the cipher uses a 26*26 table called vigenere table where the letters are shifted to the left one position using cyclic way starting with the second row. The keyword to numbers is mapped the same way. The keyword is perceived to be of any length equivalent to less than that of the plain text. Determining the length of the keyword is the first method when breaking the vigenere cipher. The key is added to the plain text in an orderly manner. When the length of the key is known, frequency analysis follows where every letter is encrypted with the same message of the key.

When the length of the key is assumed to be n and the message divided into n, then simple Caesar substitution has achieved that need to be solved. The first letter goes to the first group, the second letter goes to the latter group, and the process repeats itself until the end of the Ciphertext. If the frequency of each letter in the text correlates with English letter frequency, then in the ascending order, the largest sample size is the key for the selected group of the Ciphertext. When the essentials of each repeated Ciphertext are combined, a full key is achieved for the Ciphertext. This helps in understanding that individual letters and combinations of letters in any given stretch of language appear with varying frequencies. Encrypt, the letter chosen in the plaintext and its corresponding keyword letter, is used as the row index and column index, respectively.