Please read and follow instructions. C and C++ programming language must be used, two different codes are needed, and show results of encipher and decipher on printscreen. Please no snipit for coding.

the encryption of Vigenere with CBC can be expressed as:

Since we have modified the CBC operation for Vigenere character cipher, we have to adapt the CBC decryption too. Once one already establishes the encryption algorithm (or encipher). The general rule for the decryption algorithm (or decipher) is to run the encryption in reverse. Following this rule, we can express the decryption of Vigenere with CBC as:

Preprocessing

The plaintext input to the Vigenere CBC encipher should come from a text file. You may use any text file that is less than 4 Kilobytes in size. You can generate your text file by simply copying and pasting any text content. However, the normal text file contains upper case and lower case alphabetic characters, numbers, punctuations and other special characters including space and line feed etc.. These are way more than 26 letters defined in Vigenere cipher. So you have to preprocess the text file to eliminate all the special characters, numbers, white space and punctuations, as well as convert all upper case letters into lower case letters. The result of preprocessing should be a string of lower case letters. (as shown Figure 1) Then the encipher will use these letter sequences as the plaintext input.

This is the ciphertext which should be used for this assignment: Please make code so to remove white spaces and special characters. as statedd in instructions.

Cipher block chaining (CBC) is a mode of operation for a block cipher (one in which a sequence of bits are encrypted as a single unit or block with a cipher key applied to the entire block). Cipher block chaining uses what is known as an initialization vector (IV) of a certain length. One of its key characteristics is that it uses a chaining mechanism that causes the decryption of a block of ciphertext to depend on all the preceding ciphertext blocks. As a result, the entire validity of all preceding blocks is contained in the immediately previous ciphertext block. A single bit error in a ciphertext block affects the decryption of all subsequent blocks. Rearrangement of the order of the ciphertext blocks causes decryption to become corrupted.

In addition to the letter sequence you generated from the preprocessing. The Vigenere CBC encipher needs a key and an IV. For this assignment, you would allow the user to enter a key (key length ranges from 2 to 10) and an IV with the same length as key. You may want to mandate that the length of IV should be the same as the key. Inputs to the Vigenere CBC decipher should be the same key and IV, as well as the ciphertext. The ciphertext sequence should be generated by the Vigenere CBC encipher.

The easy way to allow the users input is using the command line arguments. For example, assuming the executable of your Vigenere CBC encipher is called V_encipher, plaintext file is called sample.txt, the key is rock and the IV is dark. The Unix command line to run the encipher would look like this:

./V_encipher sample.txt rock dark

Assuming your encipher would save the ciphertext to a file ciphertext.txt and your decipher executable is called V_decipher (the key and the IV are same as the above), the Unix command line to run the decipher would look like this:

./V_decipher ciphertext.txt rock dark

Please make key: play

Please make IV: ball

As mentioned above, you would create two programs: one for the encipher (including the preprocessing) and one for the decipher. The outputs of the encipher program should include the following:

Original text file name

Key

IV

Block size

Plaintext (after preprocessing) printed on the screen

Number of characters in plaintext (before padding)

Ciphertext printed on the screen

Name of ciphertext file (ciphertext saved to a file)

Number of padding characters

The ciphertext file will be used as one of the inputs to the decipher. The outputs of the decipher program should include the following:

Ciphertext file name

Number of characters in ciphertext

Recovered plaintext printed on the screen

Co = E (Po + IV) = (Po + IV + keyword) mod 26 Gj = E (P, + Cj-1)-(P, + Cj-1-keyword) mod 26 Co = E (Po + IV) = (Po + IV + keyword) mod 26 Gj = E (P, + Cj-1)-(P, + Cj-1-keyword) mod 26