Complete the code in c++ for b and c in the image below 3. Encryption AlgorithmThe encryption algorithm shall consist of two parts: (1) substitution, and (2) encryption on blocksof size 4 x 4 characters. The detailed description of the steps is as follows:a)PreprocessingRemove any punctuation and whitespace characters from the input.o Example:Input Text:Output Text: ENCRYPTTHISMESSAGEUSINGTHEALGORITHMDESCRIBEDBELOWb) SubstitutionKey:Input Text:Output Text:Perform a polyalphabetic substitution using the Vigenère cipher on the input file with thekey provided in the key input file.O Example:o Example:Input:WVOGJTXQHUHXICWYYMGHTRKQHQPWKYVGENCRYPT THIS MESSAGE USING THE ALGORITHM DESCRIBED BELOW.LPYSPWGOPageSIMPLEEXAMPLEKEYc) PaddingSteps d) f) are performed on blocks of size 4 x 4 characters formed from the output ofstep b (i.e., substitution). They are parts of AES and as in any block cipher, the input hasto be padded. In this particular case, pad the output from the previous step with A's sothat the length of the message is divisible by 16.ENCRYPTTHISMESSAGEUSINGTHEALGORITHMDESCRIBEDBELOWwVOGJTXQHUHXICWYYMGHTRKQHQPWKYVGLPYSPWGOINTOFOPMOOutput:WVOGJTXQHUHXICWYYMGHTRKQHQPWKYVGLPYSPWGO2>0

One way to encrypt the alphabetic text is with the Vigenere Cipher. Polyalphabetic substitution is used in its simplest form. Any substitution-based cipher that employs several substitution alphabets is said to be polyalphabetic. The original text is encrypted by employing the Vigenère square or Vigenère table. The table has the alphabet printed out 26 times in various rows, with each alphabet being cyclically moved to the left in comparison to the previous alphabet to represent the 26 potential Caesar Ciphers.The cipher switches to an alphabet from a different row at various stages during the encryption process.An ongoing keyword determines which alphabet is used at each stage. Encryption The plaintext(P) and key(K) are added modulo 26. Ei = (Pi + Ki) mod 26 Decryption Di = (Ei - Ki + 26) mod 26 program // C++ code to implement Vigenere Cipher#include<bits/stdc++.h>using namespace std; // This function generates the key in// a cyclic manner until its length isn't// equal to the length of the original text string generateKey(string str, string key){ int x = str.size(); for (int i = 0; ; i++) { if (x == i) i = 0; if (key.size() == str.size()) break; key.push_back(key[i]); } return key;} // This function returns the encrypted text// generated with the help of the keystring cipherText(string str, string key){ string cipher_text; for (int i = 0; i < str.size(); i++) { // converting in range 0-25 char x = (str[i] + key[i]) %26; // convert into alphabets(ASCII) x += 'A'; cipher_text.push_back(x); } return cipher_text;} // Driver program to test the above functionint main(){ string str = "ENCRYPTTHISMESSAGEUSINGTHEALGORITHMDESCRIBEDBELOW"; string keyword = "SIMPLEEXAMPLEKEY"; string key = generateKey(str, keyword); string cipher_text = cipherText(str, key); cout << "Ciphertext: " << cipher_text << "\n"; return 0;}1) In the main function take 2 variables one for the input message and another for the key. 2) In this code keyword and str are the string-type variable that is taken to store the key and input text. 3) Then create a key of the same size as the input pass key, str to a user-defined function generateKey as arguments generateKey(str,keyword) 4) this function will return a key of the same size as our input text. Store it into a new string type variable key. 5)Pass this new key and input text to a user-defined function cipherText(str, key) and store its return text into a variable called cipher_text . 6) Now see about generateKey function=>generateKey(str, keyword) first of all, take the size of the input string into a variable x using size() function Run an infinite for loop inside for loop check condition if the size of the input string is equal to I then assign 0 to i. again one more condition checks if key.size() equals to input string size break the for loop otherwise, make the length of the key equal to the size of the input text by putting key elements one by one into the key. This function generates the key in a cyclic manner until its length isn't equal to the length of the original text cipherText function will take 2 arguments one is the original string another one is the return value of generateKey function. string cipherText(string str, string key) take a variable cipher_text of string type. run a for loop until I become equal to the size of str. convert the range into 0-25 using (char x = (str[i] + key[i]) %26) then convert them into alphabets using (x += 'A') then insert x into cipher text string variable using (cipher_text.push_back(x)) return cipher_text D part can be done using the same logic