Cryptography/monoalphabetic cipher.cpp at main · learnnshare28/Cryptography · GitHub

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#include<bits/stdc++.h>

using namespace std;

 string sets="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'0''1''2''3''4''5''6''7''8''9' ";

 string encryption(string plaintext,string key)
 {
 	string encrypt_text="";

 	for ( int i=0;i<plaintext.length();i++)
 	{
			//alnum check wheather the character is alphanumeric or not.If the character is alphanumeric
		 // then that character is  encrypted otherwise it remain same throughout the enryption process
	 if(isalnum(plaintext[i]))
 	{
 		for(int j=0;j<sets.length();j++)
 		{

 			if(plaintext.at(i)==sets.at(j))
 			{
 				encrypt_text+=key.at(j);
 				break;
			 }
		}


		 }
		else
	encrypt_text+=char(plaintext[i]);
	 }
	 return encrypt_text;


 }
void decryption(string ciphertext,string key)

 {
 	string decrypt_text="";
 	for (int i=0;i<ciphertext.length();i++)
 	{
			//alnum check wheather the character is alphanumeric or not.If the character is alphanumeric
		 // then that character is  decrypted otherwise it remain same throughout the deryption process
 	if(isalnum(ciphertext[i]))
 	   {
 		for(int j=0;j<key.length();j++)
 		{

 			if(ciphertext.at(i)==key.at(j))
 			{
 				decrypt_text+=sets.at(j);
 				break;
			 }
		 }
		}
		else
			decrypt_text+=char(ciphertext[i]);
	 }
	 cout<<"After decryption cipher text becomes:"<<decrypt_text<<endl;


 }
 int main()
 {
 	string message ,cipher_text;
 	int choice;
 	string key="PQRSTUVWXYZABCDEFGHIJKLMNOpqrstuvwxyzabcdefghijklmno'5''6''7''8''9''0''1''2''3''4' ";

 	cout<<"Enter the message:"<<endl;
 	getline(cin,message);
 	//for display the process of interchanging of characters
 	cout<<"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz 0  1  2  3  4  5  6  7  8  9"<<endl;
 	cout<<"|||||||||||||||||||||||||||||||||||||||||||||||||||| |  |  |  |  |  |  |  |  |  |"<<endl;
 	cout<<key<<endl;

 	while(1)
 	{
 	cout<<"Enter your choice:"<<endl;
 	cout<<"1 for encryption"<<endl<<"2 for decryption"<<endl<<"3 for exit"<<endl;
 	cin>>choice;

 	switch(choice){
 	 case 1:
 		cout<<"Encryption Process Begin"<<endl;
 		cout<<"---------------------------------------------"<<endl;
 		cipher_text=encryption(message,key);
 		cout<<"After encryption process ,plaintext becomes:"<<cipher_text<<endl;
 		break;
 	case 2:
 		cout<<"Decryption Process Begin"<<endl;
 		cout<<"---------------------------------------------"<<endl;
 		cipher_text=encryption(message,key);
 		decryption(cipher_text,key);
		 break;
	case 3:
		exit(0);
		break;
	default:
		cout<<"Invalid entry!!"<<endl;


	 }

	 }
 	return 0;

 }