Add RSA Algorithm

ICS/Assignment4/RSAClient.java

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+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.math.BigInteger;
+import java.net.Socket;
+import java.net.UnknownHostException;
+import java.util.Scanner;
+import java.util.Random;
+
+public class RSAClient
+{
+
+	public static int getPublicKey(int phi)
+	{
+		Random r = new Random();
+		int result = r.nextInt(phi-2) + 2;
+		while (BigInteger.valueOf(phi).gcd(BigInteger.valueOf(result)).intValue() != 1) {
+			result = r.nextInt(phi-2) + 2;
+		}
+		return result;
+	}
+
+	public static int getPrivateKey(int phi, int e)
+	{
+		int k = 1;
+		double d = (double) (k * phi + 1) / (double) e;
+		while (Math.floor(d) != d)
+		{
+			k = k + 1;
+			d = (double) (k * phi + 1) / (double) e;
+		}
+		return (int)d;
+	}	
+
+	public static void main(String[] args) throws UnknownHostException, IOException
+	{		
+		Socket soc = new Socket("127.0.0.1",8088);
+		System.out.println("Connected to "+soc.getRemoteSocketAddress());
+		DataInputStream dis = new DataInputStream(soc.getInputStream());
+		DataOutputStream dos = new DataOutputStream(soc.getOutputStream());
+		Scanner sc = new Scanner(System.in);
+
+		System.out.print("Enter first prime number (P): ");
+		int p = sc.nextInt();
+		System.out.print("Enter second prime number (Q): ");
+		int q = sc.nextInt();
+
+		int n = p * q;
+		System.out.println("n: " + n);
+
+		int phi = (p - 1) * (q - 1);
+		System.out.println("Ø(n): " + phi);
+
+		int e = getPublicKey(phi);
+		int d = getPrivateKey(phi, e);
+
+		dos.writeInt(n);
+		dos.writeInt(e);
+
+		System.out.println("Public key {e,n} = { " + e + ", " + n + " }");
+		System.out.println("Private key {d,n} = { " + d + ", " + n + " }");
+
+		System.out.println("Waiting for Ciphertext....");
+		int cipherText = dis.readInt();
+		System.out.println("Received Ciphertext : "+cipherText);
+		BigInteger plainText = BigInteger.valueOf(cipherText).pow(d).mod(BigInteger.valueOf(n));
+
+		System.out.println("Decrypted Plain Text: "+plainText);
+
+		soc.close();
+		sc.close();		
+
+	}
+}

ICS/Assignment4/RSAServer.java

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+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.math.BigInteger;
+import java.net.ServerSocket;
+import java.net.Socket;
+import java.util.Scanner;
+
+public class RSAServer
+{	
+	public static void main(String[] args) throws IOException
+	{
+		ServerSocket server = new ServerSocket(8088);
+		System.out.println("Waiting for connection on port " + server.getLocalPort());
+		Socket soc = server.accept();
+		System.out.println("Accepted connection from " + soc.getRemoteSocketAddress());
+		DataInputStream dis = new DataInputStream(soc.getInputStream());
+		DataOutputStream dos = new DataOutputStream(soc.getOutputStream());
+
+		Scanner sc = new Scanner(System.in);
+		int n = dis.readInt();
+		int e = dis.readInt();
+		System.out.println("n = " + n + " \ne = " + e);
+
+		System.out.println("Public key {e,n} = { " + e + ", " + n + " }");
+
+		System.out.print("Enter plaintext for encryption (Numeric Form): ");
+		int plainText = sc.nextInt();
+
+		BigInteger cipherText = BigInteger.valueOf(plainText).pow(e).mod(BigInteger.valueOf(n));
+		System.out.println("Generated Ciphertext : " + cipherText);
+		dos.writeInt(cipherText.intValue());
+
+		soc.close();
+		server.close();
+		sc.close();
+	}
+}