Fix Predictable pseudorandom number generator security issue

src/main/java/org/wso2/carbon/device/mgt/iot/virtualfirealarm/agent/transport/TransportUtils.java

@@ -36,6 +36,8 @@ import java.net.ServerSocket;
 import java.net.SocketException;
 import java.net.URL;
 import java.nio.charset.StandardCharsets;
+import java.security.NoSuchAlgorithmException;
+import java.security.SecureRandom;
 import java.util.ArrayList;
 import java.util.Enumeration;
 import java.util.HashMap;
@@ -173,28 +175,27 @@ public class TransportUtils {
 	 */
 	public static synchronized int getAvailablePort(int randomAttempts) {
 		ArrayList<Integer> failedPorts = new ArrayList<Integer>(randomAttempts);
-
-		Random randomNum = new Random();
+		try {
+			SecureRandom secureRandom = SecureRandom.getInstance("SHA1PRNG");
 			int randomPort = MAX_PORT_NUMBER;
-
 			while (randomAttempts > 0) {
-			randomPort = randomNum.nextInt(MAX_PORT_NUMBER - MIN_PORT_NUMBER) + MIN_PORT_NUMBER;
-
+				randomPort = secureRandom.nextInt(MAX_PORT_NUMBER - MIN_PORT_NUMBER) + MIN_PORT_NUMBER;
 				if (checkIfPortAvailable(randomPort)) {
 					return randomPort;
 				}
 				failedPorts.add(randomPort);
 				randomAttempts--;
 			}
-
 			randomPort = MAX_PORT_NUMBER;
-
 			while (true) {
 				if (!failedPorts.contains(randomPort) && checkIfPortAvailable(randomPort)) {
 					return randomPort;
 				}
 				randomPort--;
 			}
+		} catch (NoSuchAlgorithmException e) {
+			throw new RuntimeException("SHA1PRNG algorithm could not be found.");
+		}
 	}
 
 

src/main/java/org/wso2/carbon/device/mgt/iot/virtualfirealarm/agent/virtual/VirtualHardwareManager.java

@@ -33,6 +33,8 @@ import javax.sound.sampled.Clip;
 import javax.swing.*;
 import java.io.IOException;
 import java.io.InputStream;
+import java.security.NoSuchAlgorithmException;
+import java.security.SecureRandom;
 
 /**
  * This class use to emulate virtual hardware functionality
@@ -174,19 +176,19 @@ public class VirtualHardwareManager {
     }
 
     private int getRandom(int max, int min, int current, boolean isSmoothed, int svf) {
-
         if (isSmoothed) {
             int offset = (max - min) * svf / 100;
             double mx = current + offset;
             max = (mx > max) ? max : (int) Math.round(mx);
-
             double mn = current - offset;
             min = (mn < min) ? min : (int) Math.round(mn);
         }
-
-        double rnd = Math.random() * (max - min) + min;
-        return (int) Math.round(rnd);
-
+        try {
+            SecureRandom secureRandom = SecureRandom.getInstance("SHA1PRNG");
+            return secureRandom.nextInt(max - min) + min;
+        } catch (NoSuchAlgorithmException e) {
+            throw new RuntimeException("SHA1PRNG algorithm could not be found.");
+        }
     }
 
     private void setAudioSequencer() {