diff --git a/.classpath b/.classpath
index 7bdf471..96752de 100644
--- a/.classpath
+++ b/.classpath
@@ -10,7 +10,7 @@
 	<classpathentry kind="lib" path="lib/slf4j-api-1.7.5.jar"/>
 	<classpathentry kind="lib" path="lib/slf4j-log4j12-1.7.5.jar"/>
 	<classpathentry kind="lib" path="lib/devinsy-utils-0.2.0.jar"/>
-	<classpathentry kind="lib" path="lib/commons-codec-1.8.jar"/>
+	<classpathentry kind="lib" path="lib/commons-codec-1.8.jar" sourcepath="lib/commons-codec-1.8-sources.jar"/>
 	<classpathentry kind="con" path="org.eclipse.jst.j2ee.internal.module.container"/>
 	<classpathentry kind="con" path="org.eclipse.jst.server.core.container/org.eclipse.jst.server.tomcat.runtimeTarget/Apache Tomcat v7.0">
 		<attributes>
diff --git a/src/fr/devinsy/kiss4web/SimpleSecurityAgent.java b/src/fr/devinsy/kiss4web/SimpleSecurityAgent.java
index ac83328..e5cd2cd 100644
--- a/src/fr/devinsy/kiss4web/SimpleSecurityAgent.java
+++ b/src/fr/devinsy/kiss4web/SimpleSecurityAgent.java
@@ -7,6 +7,7 @@ import org.apache.commons.codec.digest.DigestUtils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import fr.devinsy.util.StringList;
 
 /**
  *
@@ -59,6 +60,35 @@ public class SimpleSecurityAgent
 		return (result);
 	}
 
+	/**
+	 * This method builds a key from keys and a secret key.
+	 */
+	public String computeAuth(final String... keys)
+	{
+		String result;
+
+		if (keys == null)
+		{
+			result = null;
+		}
+		else
+		{
+			// Add a secret key to the key list.
+			String[] targetKeys = new String[keys.length + 1];
+			for (int keyIndex = 0; keyIndex < keys.length; keyIndex++)
+			{
+				targetKeys[keyIndex] = keys[keyIndex];
+			}
+			targetKeys[keys.length] = this.secretKey;
+
+			//
+			result = md5sum(targetKeys);
+		}
+
+		//
+		return (result);
+	}
+
 	/**
 	 * Check authentication and refresh it (reset countdown).
 	 */
@@ -75,7 +105,7 @@ public class SimpleSecurityAgent
 		{
 			result = false;
 		}
-		else if (auth.equals(computeAuth(accountId, userId, request.getRemoteAddr(), this.secretKey)))
+		else if (auth.equals(computeAuth(accountId, userId, request.getRemoteAddr())))
 		{
 			result = true;
 
@@ -91,6 +121,29 @@ public class SimpleSecurityAgent
 		return (result);
 	}
 
+	/**
+	 * 
+	 * @param source
+	 * @return
+	 */
+	public String md5sumWithSecret(final String source)
+	{
+		String result;
+
+		if (source == null)
+		{
+			result = null;
+		}
+		else
+		{
+			String key = source + this.secretKey;
+			result = md5sum(key);
+		}
+
+		//
+		return result;
+	}
+
 	/**
 	 * 
 	 */
@@ -108,7 +161,7 @@ public class SimpleSecurityAgent
 	{
 		// Refresh cookie.
 		int duration = 60 * 60;
-		String auth = computeAuth(String.valueOf(accountId), userId, request.getRemoteAddr(), this.secretKey);
+		String auth = computeAuth(String.valueOf(accountId), userId, request.getRemoteAddr());
 
 		response.addCookie(CookieHelper.buildCookie(this.authLabel, auth, duration));
 		response.addCookie(CookieHelper.buildCookie(this.accountIdLabel, accountId, duration));
@@ -133,24 +186,26 @@ public class SimpleSecurityAgent
 	/**
 	 * 
 	 */
-	static public String computeAuth(final String key1, final String key2, final String key3, final String key4)
+	static public String md5sum(final String... keys)
 	{
 		String result;
 
-		result = md5sum(key1 + key2 + key3 + key4);
+		if (keys == null)
+		{
+			result = null;
+		}
+		else
+		{
+			//
+			StringList targetKey = new StringList();
+			for (String key : keys)
+			{
+				targetKey.append(key);
+			}
 
-		//
-		return (result);
-	}
-
-	/**
-	 * 
-	 */
-	static String md5sum(final String source)
-	{
-		String result;
-
-		result = DigestUtils.md5Hex(source);
+			//
+			result = DigestUtils.md5Hex(targetKey.toString());
+		}
 
 		//
 		return (result);