diff --git a/Makefile b/Makefile
index ec38678..cc45507 100644
--- a/Makefile
+++ b/Makefile
@@ -55,7 +55,7 @@ client.o: client.cpp client.h server.h exception.h config.h worker.h auth.h time
 server.o: server.cpp server.h client.h utility.h config.h worker.h auth.h time.h echo.h tun.h tun_dev.h
 	g++ -c server.cpp $(CFLAGS)
 
-auth.o: auth.cpp auth.h sha1.h
+auth.o: auth.cpp auth.h sha1.h utility.h
 	g++ -c auth.cpp $(CFLAGS)
 
 worker.o: worker.cpp worker.h tun.h exception.h time.h echo.h tun_dev.h
diff --git a/auth.cpp b/auth.cpp
index 4063990..2721c7a 100644
--- a/auth.cpp
+++ b/auth.cpp
@@ -19,21 +19,13 @@
 
 #include "auth.h"
 #include "sha1.h"
+#include "utility.h"
 
-#include <stdlib.h>
 #include <arpa/inet.h>
 
-bool Auth::randInitialized = false;
-
 Auth::Auth(const char *passphrase)
 {
 	this->passphrase = passphrase;
-
-	if (!randInitialized)
-	{
-		srand(time(NULL));
-		randInitialized = true;
-	}
 }
 
 Auth::Response Auth::getResponse(const Challenge &challenge) const
@@ -59,7 +51,7 @@ Auth::Challenge Auth::generateChallenge(int length) const
 	challenge.resize(length);
 
 	for (int i = 0; i < length; i++)
-		challenge[i] = rand();
+		challenge[i] = Utility::rand();
 
 	return challenge;
 }
diff --git a/auth.h b/auth.h
index 922d145..ce47638 100644
--- a/auth.h
+++ b/auth.h
@@ -43,8 +43,6 @@ public:
 protected:
 	std::string passphrase;
 	std::string challenge;
-
-	static bool randInitialized;
 };
 
 #endif
diff --git a/utility.cpp b/utility.cpp
index 99bd0b0..bfc1c9e 100644
--- a/utility.cpp
+++ b/utility.cpp
@@ -19,6 +19,8 @@
 
 #include "utility.h"
 
+#include <stdlib.h>
+
 using namespace std;
 
 string Utility::formatIp(uint32_t ip)
@@ -27,3 +29,14 @@ string Utility::formatIp(uint32_t ip)
 	sprintf(buffer, "%d.%d.%d.%d", (ip >> 24) & 0xff, (ip >> 16) & 0xff, (ip >> 8) & 0xff, ip & 0xff);
 	return buffer;
 }
+
+int Utility::rand()
+{
+	static bool init = false;
+	if (!init)
+	{
+		init = true;
+		srand(time(NULL));
+	}
+	return ::rand();
+}
diff --git a/utility.h b/utility.h
index a8d210e..d9b09f7 100644
--- a/utility.h
+++ b/utility.h
@@ -26,6 +26,7 @@ class Utility
 {
 public:
 	static std::string formatIp(uint32_t ip);
+	static int rand();
 };
 
 #endif