Password authentication made stronger. Error messages more informative

org.envirocar.app/res/values/strings_activity_login.xml

@@ -22,16 +22,16 @@
     <string name="action_sign_in_register">Register</string>
     <string name="action_sign_in_short">Sign in</string>
     <string name="error_invalid_email">This email address is invalid.</string>
-    <string name="error_invalid_password">This password is too short.</string>
+    <string name="error_invalid_password">This password is too short.Password must be of atleast 6 characters.</string>
     <string name="error_incorrect_password">This password is incorrect.</string>
     <string name="error_invalid_credentials">Username or password is incorrect</string>
     <string name="error_field_required">This field is required.</string>
     <string name="error_not_connected_to_network">Not connected to network</string>
     <string name="register_progress_signing_in">Registering&#8230;</string>
     <string name="error_passwords_not_matching">The passwords do not match.</string>
-    <string name="error_invalid_username">This username is too short.</string>
+    <string name="error_invalid_username">This username is too short.Username must be  of atleast 6 characters.</string>
     <string name="error_username_contain_special">Special symbol not allowed except underscore</string>
-    <string name="error_field_weak_password">Password must contain at least one uppercase letter, one lowercase letter and one digit</string>
+    <string name="error_field_weak_password">Password must contain at least one uppercase letter, one lowercase letter , one digit and one special character</string>
 
     <string name="error_username_already_in_use">This username is already in use.</string>
     <string name="error_email_already_in_use">This email is already in use.</string>

org.envirocar.app/src/org/envirocar/app/views/login/SignupActivity.java

@@ -81,7 +81,7 @@ public class SignupActivity extends BaseInjectorActivity {
     private static final Logger LOG = Logger.getLogger(SignupActivity.class);
 
     private static final String EMAIL_REGEX = "^[_A-Za-z0-9-\\+]+(\\.[_A-Za-z0-9-]+)*@[A-Za-z0-9-]+(\\.[A-Za-z0-9-]+)*(\\.[A-Za-z]{2,})$";
-    private static final String PASSWORD_REGEX = "^(?=.*?[A-Z])(?=.*?[a-z])(?=.*?[0-9]).{6,}$";
+    private static final String PASSWORD_REGEX = "^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%^&+=])(?=\\S+$).{6,}$";
     private static final String USERNAME_REGEX = "^[A-Za-z0-9_-]{6,}$";
     private static final int CHECK_FORM_DELAY = 750;
     private static Drawable errorPassword;