A new method of lossless Secure Data Aggregation for Wireless Sensor Network is presented. Secure Data Aggregation is achieved using the popular Chinese Remainder theorem. Here, an ‘Augmented Chinese Remainder System’ is introduced that incorporates additional features to enforce a higher level of security to the aggregated data. The scheme provides inbuilt signature verification and eliminates the need for separate data validation algorithms. The method achieves data integrity and authentication simultaneously in addition to lossless data aggregation for the data forwarded from the Cluster Head to the Base Station. The aggregate contains the entire individual data from sensors in the encrypted form and the receiver deaggregates it to get the original data in full without any loss. The Augmented Chinese Remainder System can be extended to secure Multi-level Data Aggregation for WSN.