/* An inelegant program which encrypts and decrypts text using a secret key. Here I am playing the
parts of both Bob and Alice as a demonstration only but usually you would only be either Alice or Bob*/

import java.io.*;  //This is the java input output library

public class NoKeyExchangeEncryption
{
	static String Aencryptdecrypt(String p,int ed)
	{
		String Akey="Umbrellas keep you dry when it is raining outside";   //This phrase is Alice's "key"
		int Akeylength=Akey.length();
		String t="";
		for(int i=0;i<p.length();i++)   //this looks at each character in the plaintext in turn
		{
			int current = p.charAt(i);  //first we read the character into a variable called current
										//since current is an int variable this stores the ASCII
			if(ed==1)
			current = current+Akey.charAt(i%Akeylength);  //we add the current value onto the key value at the same position.
			else											//if the plaintext is longer than the key then we rap-around to the start of the key phrase again

			current = current-Akey.charAt(i%Akeylength);	//if ed=1 we encrypt by adding otherwise we decrypt by subtracting

			t=t+((char)(current));
		}
		return(t);
	}


	static String Bencryptdecrypt(String p,int ed)
	{
		String Bkey="Many hands make light work but not if the bulb is broken";   //This phrase is Bob's "key"
		int Bkeylength=Bkey.length();
		String t="";
		for(int i=0;i<p.length();i++)   //this looks at each character in the plaintext in turn
		{
			int current = p.charAt(i);  //first we read the character into a variable called current
										//since current is an int variable this stores the ASCII
			if(ed==1)
			current = current+Bkey.charAt(i%Bkeylength);  //we add the current value onto the key value at the same position.
			else											//if the plaintext is longer than the key then we rap-around to the start of the key phrase again

			current = current-Bkey.charAt(i%Bkeylength);	//if ed=1 we encrypt by adding otherwise we decrypt by subtracting

			t=t+((char)(current));
		}
		return(t);
	}




	/*This is the main program.*/
	public static void main(String[] args) throws IOException
	{
		BufferedReader in =new BufferedReader(new InputStreamReader(System.in));  //reader for keyboard

		System.out.println("Enter your plaintext: ");
		String s=in.readLine();   // string s now contains the plaintext
		System.out.println();
		System.out.println();
		System.out.println("Send this message to Bob");
		String c1=Aencryptdecrypt(s,1);  //the 1 means encrypt
		System.out.println(c1);
		System.out.println();
		System.out.println();
		String c2=Bencryptdecrypt(c1,1);
		System.out.println("Send this message to Alice");
		System.out.println(c2);
		System.out.println();
		System.out.println();
		String c3=Aencryptdecrypt(c2,2);  //the 2 means decrypt
		System.out.println("Send this message to Bob");
		System.out.println(c3);
		System.out.println();
		System.out.println();
		String c4=Bencryptdecrypt(c3,2);
		System.out.println("The message is:");
		System.out.println();
		System.out.println(c4);
	}
}