Question

use C++

You will implement the following encryption and decryption functions/programs for the Caesar cipher. Provide the following inputs and outputs for each function/program:

EncryptCaesar

• Two inputs:

  • A string of the plaintext to encrypt

  • A key (a number)

    ▪ For the Caesar cipher: This will indicate how many characters to shift (e.g. for a key=3, A=>D, B=>E, ..., X=>A, Y=>B, Z=>C). Note that the shift is circular.

• One output:
  ◦ A string of the ciphertext or codeword

  DecryptCaesar

• Two inputs:
  ◦ A string of the ciphertext to decrypt ◦ The key (a number)

• One output:
  ◦ A string of the plaintext

  Obviously, for this assignment to be successful, the decryption function/program must decrypt the original message which was encrypted by the encryption function/program. Or, for a plaintext P and an encryption function E() and a decryption function D(), P = D( E(P, Key), Key)

Answer 1

• Code Snippet Without Text-

• Code With Text-

//required libraries are included
#include <iostream>
#include <algorithm>
#include <string.h>
#include <map>

using namespace std;

//start of main function
int main()
{   
//declarations and initialisations
string plain_text,cipher_text;
int key_p,key_c,size_plain_text, size_cipher_text;
int value1,value2,j,i;
char value_char;
  
//reference list of characters
char my_list[]={'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'};
  
   cout<<"Enter a Plain String to Encrypt-"<<endl;
   cin>>plain_text;
   cout<<"Enter the Key for Encryption-"<<endl;
   cin>>key_p;
  
   cout<<"Enter a Cipher String to Decrypt-"<<endl;
   cin>>cipher_text;
   cout<<"Enter the Key for Decryption-"<<endl;
   cin>>key_c;
  
   //size of texts are found here
   size_plain_text=plain_text.size();
   size_cipher_text=cipher_text.size();
  
   char encrypted_text[size_plain_text],decrypted_text[size_cipher_text];
  
   //Encryption Loop
   for(i=0;i<size_plain_text;i++)
   {
   //Caesar Encryption Functional Statements
   value1=plain_text[i];
   value1=value1-65;
  
   value1=value1+key_p;
   value1=value1%26;
  
  
   encrypted_text[i]=my_list[value1];
  
   }
  
   //Decryption Loop
   for(j=0;j<size_cipher_text;j++)
   {
  
   //Caesar Decryption Functional Statements
   value2=cipher_text[j];
   value2=value2-65;
  
   value2=value2-key_p;
   if(value2<0)
   {
   value2=26+value2;
   }
  
   decrypted_text[j]=my_list[value2];
  
   }
  
   cout<<"Encrypted Text is: "<<encrypted_text<<endl;
   cout<<"Decrypted Text is: "<<decrypted_text<<endl;
  
   return 0;
}

• Input/Output Snippet-

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