One of the shortcomings of NFS is that users and systems may be impersonated. Making NFS secure requires assuring that unauthorized users cannot access files stored on secure servers. Secure NFS improves the authentication of NFS requests by using Secure RPC. Secure RPC uses the Data Encryption Standard (DES) and exponential key exchange to verify each NFS RPC request. Section 10.4.6 describes Secure RPC in detail.