soni4

Practical No : 04
Aim :Write a program to implement RSA algorithm to perform encryption / decryption of a given string.

Input ;

using System;
usingSystem.Collections.Generic;
usingSystem.Linq;
usingSystem.Text;

namespace ConsoleApplication6
{
class Program
    {
static bool IsPrime(intiNumber)
        {
intiCount;
int f = 0;
iCount = 2;
if (iNumber< 2)
return true;
while (iCount<= (iNumber / 2))
            {
if (iNumber % iCount == 0)
                {
                    f = 1;
break;
                }
iCount++;
            }
if (f == 0) return true;
return false;
        }
staticint Multiply(int iNum1, int iNum2)
        {
return iNum1 * iNum2;
        }
staticintfind_E(intiNum)
        {
intiCount = 2;
while (iCount<iNum)
            {
if (iNum % iCount != 0)
returniCount;
iCount++;
            }
return 0;
        }
staticintFind_D(int pie, int e)
        {
int k = 1;
intdvalue = 0;
bool state = true;
while (state)
            {
if ((k * pie + 1) % e == 0)
                {
dvalue = (k * pie + 1) / e;
state = false;
                }
                ++k;
            }
returndvalue;
        }
staticintFind_Text(int iNum1, int iNum2, int iNum3)
        {
intiCount, t;
iCount = 1;
            t = 1;
while (iCount<= iNum2)
            {
                t = t * iNum1;
                t = t % iNum3;
iCount++;
            }
return (t % iNum3);
        }
static void Main(String[] args)
        {
int p, q, n, d, e, pi, pt, ct;
            //clrscr();
Console.WriteLine("------IMPLIMENTATION OF R.S.A ALGORITHM------");
Console.WriteLine("Enter a prime number:");
            p = Convert.ToInt32(Console.ReadLine());
Console.WriteLine("Enter another prime number:");
            q = Convert.ToInt32(Console.ReadLine());
if (IsPrime(p) &&IsPrime(q))
            {
                n = Multiply(p, q);
Console.WriteLine("/*Intermediate Calculation..");
Console.WriteLine("n:" + n);
pi = Multiply(p - 1, q - 1);
Console.WriteLine("pi:" + pi);
                e = find_E(pi);
Console.WriteLine("e:" + e);
                d = Find_D(pi, e);
Console.WriteLine("d:" + d);
Console.WriteLine("*/");
Console.WriteLine();
Console.WriteLine();
Console.WriteLine("----KEYS---");
Console.WriteLine("Public Key:({0},{1})", e, n);
Console.WriteLine("Private Key:(" + d + "," + n + ")");
Console.WriteLine();
Console.WriteLine("----ENCRYPTION----");
Console.WriteLine("Enter the Number to Encrypt");
pt = Convert.ToInt32(Console.ReadLine());
ct = Find_Text(pt, e, n);
pt = Find_Text(ct, d, n);
Console.WriteLine("Cipher Text:" + ct);
Console.WriteLine("----Decryption---");
Console.WriteLine("Plain Text:" + pt);
            }
else
            {
Console.WriteLine("Error! Enter two prime numbers!");
            }
Console.Read();
        }
    }
}