diff --git a/src/main/java/envoy/server/processors/LoginCredentialProcessor.java b/src/main/java/envoy/server/processors/LoginCredentialProcessor.java
index 4a7f2c8..9020937 100644
--- a/src/main/java/envoy/server/processors/LoginCredentialProcessor.java
+++ b/src/main/java/envoy/server/processors/LoginCredentialProcessor.java
@@ -3,14 +3,18 @@ package envoy.server.processors;
 import java.io.IOException;
 import java.util.Arrays;
 import java.util.Date;
+import java.util.InputMismatchException;
 import java.util.List;
 import java.util.stream.Collectors;
 
+import javax.persistence.NoResultException;
+
 import envoy.data.Contacts;
 import envoy.data.LoginCredentials;
 import envoy.data.Message.MessageStatus;
 import envoy.data.User;
 import envoy.data.User.UserStatus;
+import envoy.event.HandshakeRejectionEvent;
 import envoy.server.ConnectionManager;
 import envoy.server.ObjectProcessor;
 import envoy.server.data.Message;
@@ -40,7 +44,7 @@ public class LoginCredentialProcessor implements ObjectProcessor<LoginCredential
 		UserStatusChangeProcessor.setWriteProxy(writeProxy);
 		System.out.println(String.format("Received login credentials %s from socket ID %d", input, socketId));
 
-		envoy.server.data.User user = getUser(input);
+		envoy.server.data.User user = getUser(input, writeProxy);
 
 		// Not logged in successfully
 		if (user == null) return;
@@ -72,23 +76,57 @@ public class LoginCredentialProcessor implements ObjectProcessor<LoginCredential
 		}
 	}
 
-	private envoy.server.data.User getUser(LoginCredentials credentials) {
-		envoy.server.data.User user;
+	private envoy.server.data.User getUser(LoginCredentials credentials, ObjectWriteProxy writeProxy) throws IOException {
+		return credentials.isRegistration() ? newUser(credentials) : checkForExistingUser(credentials, writeProxy);
+	}
 
-		if (credentials.isRegistration()) {
-			user = new envoy.server.data.User();
-			user.setName(credentials.getName());
-			user.setLastSeen(new Date());
-			user.setStatus(User.UserStatus.ONLINE);
-			user.setPasswordHash(credentials.getPasswordHash());
-			user.setContacts(PersistenceManager.getPersistenceManager().getContacts(user));
-			persistenceManager.addUser(user);
-		} else {
-			user = persistenceManager.getUserByName(credentials.getName());
-			// TODO: Implement error when user does not exist
-			if (!Arrays.equals(credentials.getPasswordHash(), user.getPasswordHash())) // TODO: Wrong Password Response
+	/**
+	 * @param credentials the input to evaluate
+	 * @param writeProxy  the {@link ObjectWriteProxy} to use if login was not
+	 *                    successful
+	 * @throws IOException if sending the failed login back to the client failed
+	 * @since Envoy Server Standalone v0.1-alpha
+	 */
+	private envoy.server.data.User checkForExistingUser(LoginCredentials credentials, ObjectWriteProxy writeProxy) throws IOException {
+		envoy.server.data.User	user;
+		ConnectionManager		connectionManager	= ConnectionManager.getInstance();
+		long					userId				= credentials.getId();
+		long					socketId			= connectionManager.getSocketId(userId);
+		try {
+			// Checking if user is already online
+			if (connectionManager.isOnline(userId)) {
+				writeProxy.write(socketId, new HandshakeRejectionEvent(HandshakeRejectionEvent.ALREADY_ONLINE));
 				return null;
+			}
+			user = persistenceManager.getUserById(userId);
+			// Evaluating the correctness of the password hash
+			if (!Arrays.equals(credentials.getPasswordHash(), user.getPasswordHash()))
+				throw new InputMismatchException("User " + credentials.getName() + "tried logging in using a wrong password");
+			return user;
+		} catch (NoResultException e) {
+			// Checking if user exists
+			writeProxy.write(socketId, new HandshakeRejectionEvent(HandshakeRejectionEvent.USER_DOES_NOT_EXIST));
+		} catch (InputMismatchException e) {
+			// Checking if the given password hash is correct
+			writeProxy.write(socketId, new HandshakeRejectionEvent(HandshakeRejectionEvent.INCORRECT_PASSWORD));
 		}
+		return null;
+	}
+
+	/**
+	 * @param credentials the credentials upon which to create the new {@link User}
+	 * @return the newly created {@link User}
+	 * @since Envoy Server Standalone v0.1-alpha
+	 */
+	private envoy.server.data.User newUser(LoginCredentials credentials) {
+		envoy.server.data.User user;
+		user = new envoy.server.data.User();
+		user.setName(credentials.getName());
+		user.setLastSeen(new Date());
+		user.setStatus(User.UserStatus.ONLINE);
+		user.setPasswordHash(credentials.getPasswordHash());
+		user.setContacts(PersistenceManager.getPersistenceManager().getContacts(user));
+		persistenceManager.addUser(user);
 		return user;
 	}
 }