// HelloWorldProgram.cs
//

using System;
using System.Collections.Generic;
#if (DEBUG)
using System.Diagnostics;
#endif // #if (DEBUG)
using System.Text;
using BroccoliProducts.Maths;

namespace HelloWorldProgram
{

	/////////////////////////////////////////////////////////////////
	// declaration of Program class

	class HelloWorldProgram
	{

		/////////////////////////////////////////////////////////////
		// main function

		static void Main(string[] args)
		{

			// declaration of local variables
			Random rnd = new Random();
			JumboInteger Temp = null;

			// declare a format for displaying jumbo-integers in hexidecimal
			JumboInteger.eStringFormat fmt = JumboInteger.eStringFormat.Hexidecimal | JumboInteger.eStringFormat.AddSeperators | JumboInteger.eStringFormat.OmitBaseTag;

			// comment in this line to see all number as decimal values instead of hexidecimal
			fmt = JumboInteger.eStringFormat.Decimal;

			// display message
			Console.WriteLine("HelloWorldProgram started...");
			Console.WriteLine("* * *  Generating large prime numbers can take a few minutes.  * * *");

			/////////////////////////////////////////////////////////
			// A - Convert our message into a number

			// the message M
			String strMessage = "Hello World!";
			Console.WriteLine("\nMessage (M) = {0}", strMessage);

			// convert M to an array of bytes
			byte[] bufferPlainText = Encoding.Unicode.GetBytes(strMessage);
			JumboInteger M = new JumboInteger();
			M.SetRaw(bufferPlainText);
			Console.WriteLine("\nMessage (M) as a number\nM = {0}", M.ToString(fmt));

			/////////////////////////////////////////////////////////
			// B - Generate two distinct prime numbers p and q

			// use 512 bit prime numbers 
			// our message is 12*2 bytes (Unicode chars), 192 bits, so 512 bits is more than is needed
			UInt32 uiBits = 512;

			// choose prime number p
			Console.WriteLine("\nChoosing prime number p...");
			JumboInteger p = new JumboInteger();
			p.MakeRandomPrime(uiBits);
			Console.WriteLine("p = {0}", p.ToString(fmt));

			// chose prime number q, which must not be the same as q
			Console.WriteLine("\nChoosing prime number q...");
			JumboInteger q = new JumboInteger();
			while (true)
			{

				// find a prime q
				q.MakeRandomPrime(uiBits);

				// ok, as long as p != q
				if (p != q)
					break;

			}
			Console.WriteLine("q = {0}", q.ToString(fmt) );

			/////////////////////////////////////////////////////////
			// C - Calculate N = p x q
			JumboInteger N = p * q;
			Console.WriteLine("\nN = p * q\nN = {0}", N.ToString(fmt));

			/////////////////////////////////////////////////////////
			// D - choose e and d

			// calculate phi = (p-1) * (q-1)
			JumboInteger phi = (p - 1) * (q - 1);
			Console.WriteLine("\nphi = (p-1) * (q-1)\nphi = {0}", phi.ToString(fmt));

			// calculate the maximum value for e, between 1 and min(64000,N)
			Int32 iMax_e = 64000;
			if (N < 64000)
				iMax_e = N.ToInt32() - 1;

			// loop until a valid e and d are found
			JumboInteger e = new JumboInteger();
			JumboInteger d = new JumboInteger();
			while (true)
			{

				// pick an e between 3 and maximum-e
				e.SetInt32(rnd.Next(3, iMax_e));

				// e must be relatively prime to phi (gcd(phi,e)==1)
				Temp = JumboInteger.Gcd(e, phi);
				if (Temp != 1)
					continue;

				// pick d, so that ed ==1 % phi
				d = JumboInteger.ModularInverse(e, phi);

				// break out of loop
				break;

			} // while-loop
			Console.WriteLine("\ne = {0}", e.ToString(fmt));
			Console.WriteLine("\nd = {0}", d.ToString(fmt));

			/////////////////////////////////////////////////////////
			// E - dump key-pair
			Console.WriteLine("\nPUBLIC KEY [e,N]\nKey = [{0}, {1}]", e.ToString(fmt), N.ToString(fmt));
			Console.WriteLine("\nPRIVATE KEY [d]\nKey = [{0}]", d.ToString(fmt));

			/////////////////////////////////////////////////////////
			// F - calculate cypherText C
			JumboInteger C = M.PowerMod(e, N);
			Console.WriteLine("\nCypher-text (C) as a number\nC = {0}", C.ToString(fmt));

			/////////////////////////////////////////////////////////
			// G - decrypt the cypher-text C into plain-text M2

			// calculate M2 = (C ^ d) % N
			JumboInteger M2 = C.PowerMod(d, N);
			Console.WriteLine("\nDecyphered plain-text (M2) as a number\nM2 = {0}", M2.ToString(fmt));

			// convert M2 into a text string
			String strPlainText = Encoding.Unicode.GetString(M2.ToRaw());
			Console.WriteLine("\nPlain text (M2) = {0}", strPlainText);

			/////////////////////////////////////////////////////////
			// application finished

			Console.WriteLine("\nHelloWorldProgram finished.");
			Console.WriteLine("Click any key to close...");
			while (!Console.KeyAvailable) { }

		}

	}

}