= NTS Quick Start Guide
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== Related Links

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== Table of Contents

* link:#introduction[Introduction]
* link:#client[NTS Client Configuration]
* link:#server[NTS Server Configuration]
* link:#verify[Verification]
* link:#refer[References]

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[[introduction]]
== Introduction

NTS is a method for using TLS/SSL to authenticate NTP traffic on the net.
That means that bad guys can't forge packets that will give your
system bogus time.

The RFC hasn't been published yet (December 2019).  Nothing has changed
recently, but there may be minor adjustments when it is finalized.

Note: The NTP Pool does not currently support NTS.

It is strongly suggested that you get a "normal", unauthenticated,
NTP server working before enabling NTS.  This may reduce the time
spent debugging.  See the link:quick.adoc[Client Quick Start Guide].

[[client]]
== NTS Client Configuration

Append the keyword `nts` to the end of your `server` lines.  Do this only for
servers that speak NTS.  If the server uses a port other than 123 for NTS key
exchange, you also need to specify the port number.  As of December 2019, the
following should work:

Public NTP servers supporting NTS:

------------------------------------------------------------
server time.cloudflare.com:1234 nts	# Global, anycast
server nts.ntp.se:4443 nts		# Sweden
------------------------------------------------------------

CloudFlare supports only TLS 1.3.  To use TLS 1.3, you must have OpenSSL 1.1.1
or higher.

Development machines, so there may be gaps in availability:

------------------------------------------------------------
server ntpmon.dcs1.biz nts	# Singapore
server ntp1.glypnod.com nts	# San Francisco
server ntp2.glypnod.com nts	# London
------------------------------------------------------------


Note that you must use the same host name that was used to create
the server's certificate.  IP addresses will not work.

This assumes that the server is using a certificate covered by
your OS/distro's root certificate collection.

NetBSD needs the +mozilla-rootcerts-openssl+ package and `ca /etc/openssl/certs/` added to the +server+ line.

Restart `ntpd`, and skip to link:#verify[Verification], below.

[[server]]
== NTS Server Configuration

Being an NTS server requires a well-formed SSL certificate.  The
easiest way to do this is to use Let's Encrypt.  It needs a FQDN.
Please see the
https://certbot.eff.org/[certbot client site] for instructions.

The following worked on Fedora:

------------------------------------------------------------
$ sudo dnf install certbot

# Install
$ sudo certbot certonly --standalone

# Renew
$ sudo certbot renew
$ sudo killall -HUP ntpd
------------------------------------------------------------

If you already have an SSL certificate for your server, and you are
serving time using the same FQDN, you can reuse that certificate.

Next, add the line:
`nts enable`
to your +{ntpconf}+ file.

Locate the following two files:

* Your certificate private key
* Your certificate chain (i.e. your certificate followed by any intermediate
  CA certificates)

Then add the lines below to your +{ntpconf}+, replacing
with your pathnames.

Example, using Let's Encrypt:

------------------------------------------------------------
nts key /etc/letsencrypt/live/ntp.example.com/privkey.pem
nts cert /etc/letsencrypt/live/ntp.example.com/fullchain.pem
------------------------------------------------------------

Note that `ntpd` must be able to read both files and you want to
make sure that the bad guys can't read your private key.  It may
be simpler to copy those files over to `/etc/ntp/` and adjust
their owner and mode so `ntpd` running as user `ntp` can read them.

You may need to tell your system where to store the keys used
to encrypt cookies.  The default is `/var/lib/ntp/nts-keys`.
Some distros use `/var/db/` rather than `/var/lib/`.

------------------------------------------------------------
nts cookie /var/lib/ntp/nts-keys
------------------------------------------------------------

Again, make sure the bad guys can't read that file.

Restart your server, and skip to link:#verify[Verification], below.


[[verify]]
== Verification

Check your log file.  The current client side NTS implementation
is quite chatty.  The log lines may change, but what you see should be
similar to below.

As a client, you should see lines like this:

------------------------------------------------------------
2019-03-22T08:06:33 ntpd[12915]: DNS: dns_probe: pi3.rellim.com, cast_flags:1, flags:21801
2019-03-22T08:06:33 ntpd[12915]: NTSc: DNS lookup of pi3.rellim.com took 0.003 sec
2019-03-22T08:06:33 ntpd[12915]: NTSc: nts_probe connecting to pi3.rellim.com:ntp => 204.17.205.23:123
2019-03-22T08:06:34 ntpd[12915]: NTSc: Using TLSv1.2, AES256-GCM-SHA384 (256)
2019-03-22T08:06:34 ntpd[12915]: NTSc: certificate subject name: /CN=pi3.rellim.com
2019-03-22T08:06:34 ntpd[12915]: NTSc: certificate issuer name: /C=US/O=Let's Encrypt/CN=Let's Encrypt Authority X3
2019-03-22T08:06:34 ntpd[12915]: NTSc: certificate is valid.
2019-03-22T08:06:34 ntpd[12915]: NTSc: read 880 bytes
2019-03-22T08:06:34 ntpd[12915]: NTSc: Got 8 cookies, length 104, aead=15.
2019-03-22T08:06:34 ntpd[12915]: NTSc: NTS-KE req to pi3.rellim.com took 0.882 sec, OK
------------------------------------------------------------

For initializing a server, you should see lines like this:

------------------------------------------------------------
27 Dec 12:03:47 ntpd[962738]: INIT: OpenSSL 1.1.1d FIPS  10 Sep 2019, 1010104f
27 Dec 12:03:47 ntpd[962738]: NTSs: starting NTS-KE server listening on port 123
27 Dec 12:03:47 ntpd[962738]: NTSs: loaded certificate (chain) from /etc/ntp/fullchain.pem
27 Dec 12:03:47 ntpd[962738]: NTSs: loaded private key from /etc/ntp/privkey.pem
27 Dec 12:03:47 ntpd[962738]: NTSs: Private Key OK
27 Dec 12:03:47 ntpd[962738]: NTSs: OpenSSL security level is 1
27 Dec 12:03:47 ntpd[962738]: NTSs: listen4 worked
27 Dec 12:03:47 ntpd[962738]: NTSs: listen6 worked
27 Dec 12:03:47 ntpd[962738]: NTSc: Using system default root certificates.
------------------------------------------------------------

On a server, each time a client uses TLS to setup cookies,
you should see lines like these.  If all goes well, there is a single
line for each connection.

------------------------------------------------------------
 1 Dec 22:42:21 ntpd[237777]: NTSs: NTS-KE from 192.168.1.71:43560, Using TLSv1.3, TLS_CHACHA20_POLY1305_SHA256 (256), took 0.018 sec
 1 Dec 22:42:56 ntpd[237777]: NTSs: NTS-KE from 192.168.1.61:33930, Using TLSv1.2, ECDHE-RSA-AES256-GCM-SHA384 (256), took 0.075 sec
------------------------------------------------------------

Servers on the big bad internet will get a lot of garbage connections.
The common cases produce a single line.  Less common cases will have additional lines with OpenSSL error data.

------------------------------------------------------------
26 Dec 18:13:55 ntpd[940892]: NTSs: SSL accept from 68.134.33.4:52188 failed: wrong version number, took 0.000 sec
26 Dec 18:24:20 ntpd[940892]: NTSs: SSL accept from 64.139.1.69:56525 failed, took 0.101 sec
26 Dec 18:24:20 ntpd[940892]: NTS: error:14094418:SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca
------------------------------------------------------------

`alert` means the client on the other end encountered troubles and is
reporting them back to the server.

The logging prefix *NTSs* is for the NTS server component.  The *NTSc*
component is for the NTS client part, where you are talking to NTS servers.

=== Check with ntpq

The output of ntpq will be slightly different when NTS is in use,
note the `t` column.  Example:

------------------------------------------------------------
root@ntpmon:/var/www/html/ntp# ntpq -p
     remote                                   refid      st t when poll reach   delay   offset   jitter
*SHM(1)                                  .PPS.            0 l   20   64  377   0.0000   0.0007   0.0281
xSHM(0)                                  .GPS.            0 l   19   64  377   0.0000 233.3966  19.2212
+pi3.rellim.com                          .PPS.            1 8   56   64  371 197.4484   0.0932   0.9660
+kong.rellim.com                         204.17.205.17    2 8   17   64  273 210.7230  -1.3924   0.6086
-ntp1.glypnod.com                        204.123.2.72     2 8   50   64  277 178.5749   3.8921   0.9611
-ntp2.glypnod.com                        17.253.34.253    2 8    -   64  177 185.7582  -2.6534   0.0275
 2407:8000:8001:80::8                    .DNS.           16 u    - 1024    0   0.0000   0.0000   0.0005
-navobs1.wustl.edu                       .GPS.            1 u  105   64  356 221.5282  -2.4354   0.0293
------------------------------------------------------------

The `t` column shows how many cookies your NTS client is holding for the
appropriate servers.  The number should be 8. Lower numbers indicate dropped
packets.  (7 could be a packet in flight.)

The RFC calls for the server to rotate the private key used to
encrypt cookies every 24 hours.  The server also saves the previous
key so old cookies will work for at least 24 hours.  24 hours and 8 cookies
will work for a polling interval of up to 3 hours.  That's much longer
than the default +maxpoll+ of 10 (1024 seconds).

=== Check ntp variables

Try `ntpq -c nts`. This will show various counters related
to NTS.  This feature is under active development, so the
format might change.  An example:

------------------------------------------------------------
root@ntpmon:/var/www/html/ntp# ntpq -c nts
NTS client sends:            7491
NTS client recvs:            6562
NTS client recvs w error:    0
NTS server recvs:            5591
NTS server recvs w error:    38
NTS server sends:            5553
NTS make cookies:            6392
NTS decode cookies:          4734
NTS decode cookies old:      819
NTS decode cookies too old:  0
NTS decode cookies error:    0
NTS KE probes:               8
NTS KE probes_bad:           0
NTS KE serves:               75
NTS KE serves_bad:           56
------------------------------------------------------------


[[refer]]
== References


* https://datatracker.ietf.org/doc/draft-ietf-ntp-using-nts-for-ntp/[Current Status of NTS Draft]
* https://developers.cloudflare.com/time-services/nts/usage/[Cloudflare Public NTS Servers]
* https://www.netnod.se/blog/what-network-time-security-and-why-it-important[Netnod NTS Service]
* https://datatracker.ietf.org/meeting/106/materials/slides-106-ntp-nts-deployment-03.pdf[Deployment Review]

'''''

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