Somewhat topical: in case you want authenticated access to NIST NTP servers, you need to send a letter to NIST using the US mail or FAX machine (e-mail is not acceptable).
NIST will reply with a key number and a key value. The reply will be by US mail only, e-mail will never be used.
The office that normally receives US mail and FAX messages currently has limited access, which may result in significant delays in processing requests
NIST will reply with a key number and a key value. The reply will be by US mail only, e-mail will never be used.
The office that normally receives US mail and FAX messages currently has limited access, which may result in significant delays in processing requests
https://www.nist.gov/pml/time-and-frequency-division/time-se...
(things you discover when you implement fedramp)