NTP authentication is not the same as NTP encryption. NTP (Network Time Protocol) authentication uses symmetric keys such as MD5 or SHA message digests to add a cryptographic checksum (message authentication code) to the request packet. The server uses the shared key to verify that the request came from an authorized client before replying. However, the reply itself is neither authenticated nor encrypted, and no cryptographic proof is included in the server’s response. This means an attacker can still forge replies or replay old responses, because the client has no way to verify that a response came from the legitimate server. In other words, traditional authentication provides only limited protection and does not ensure confidentiality or strong integrity of the time data. If secure time synchronization is needed, modern NTP deployments should use NTS (Network Time Security) where available, as it provides robust encryption and authentication specifically designed for NTP.