3.3 KiB
| title | excerpt | date | tags | |
|---|---|---|---|---|
| Configuring NTS in OpenWRT | Obtain time in an authenticated manner | 2024-10-12 |
|
Network Time Security (NTS) is a security extension to the Network Time Protocol (NTP) to provide integrity and authenticity using TLS, and other features. Despite the use of TLS, NTS does not provide confidentiality as the NTP data itself is not encrypted. Other security extension (unrelated to NTP) like DNSSEC also does not provide confidentiality because the DNS data is not encrypted. Even TLS itself is not fully encrypted because Client Hello is still sent in the clear, at least until Encrypted Client Hello is standardised.
Back to OpenWRT, first SSH into the device.
Disable sysntpd so that there is only one NTP client.
service sysntpd stop
service sysntpd disable
Install chrony-nts package, chrony package does not support NTS.
opkg update
opkg install chrony-nts
Disable NTP in chrony.
uci set chrony.@pool[0].disabled='1'
uci set chrony.@dhcp_ntp_server[0].disabled='1'
Add NTS servers, preferably at least two and they are geographically close.
uci set chrony.cloudflare='server'
uci set chrony.cloudflare.hostname='time.cloudflare.com'
uci set chrony.cloudflare.iburst='yes'
uci set chrony.cloudflare.nts='yes'
uci set chrony.netnod='server'
uci set chrony.netnod.hostname='nts.netnod.se'
uci set chrony.netnod.iburst='yes'
uci set chrony.netnod.nts='yes'
Use NTS only.
# Require at least 2 reachable sources
minsources 2
# Use NTS sources only
authselectmode require
# Disable chronyc remote access
cmdport 0
Preserve the config during upgrade.
echo "/var/etc/chrony.d/20-nts.conf" >> /etc/sysupgrade.conf
Commit the changes and restart the daemon.
uci commit chrony
service chronyd restart
Verify the config.
cat /etc/config/chrony
config pool
option hostname '2.openwrt.pool.ntp.org'
option maxpoll '12'
option iburst 'yes'
option disabled 'yes'
config dhcp_ntp_server
option iburst 'yes'
option disabled 'yes'
config server cloudflare
option hostname 'time.cloudflare.com'
option iburst 'yes'
option nts 'yes'
config server netnod
option hostname 'nts.netnod.se'
option iburst 'yes'
option nts 'yes'
config allow
option interface 'lan'
config makestep
option threshold '1.0'
option limit '3'
config nts
option rtccheck 'yes'
option systemcerts 'yes'
cat /var/etc/chrony.d/10-uci.conf
server time.cloudflare.com iburst nts
server nts.netnod.se iburst nts
allow 192.168.1.1/24
makestep 1.0 3
nocerttimecheck 1
chronyc sources
MS Name/IP address Stratum Poll Reach LastRx Last sample
===============================================================================
^* time.cloudflare.com 3 6 17 13 -1188us[-1395us] +/- 11ms
^- nts.netnod.se 2 6 17 13 +229us[ +22us] +/- 85ms
Lastly, highly recommend to hardcode the IP address of the chosen NTP servers into "/etc/hosts", especially when using DNSSEC-validating DNS client, to avoid unresolvable NTS domains when the time is not correct.