NTP Symmetric Key

NTP’s Symmetric Key File User Manual

This document describes the symmetric key file for the NTP Project’s ntpd program.

This document applies to version 4.2.8p18 of ntp.keys.

Short Table of Contents

1 Description

The name and location of the symmetric key file for ntpd can be specified in a configuration file, by default /etc/ntp.keys.

1.1 Notes about ntp.keys

This document describes the format of an NTP symmetric key file. For a description of the use of this type of file, see the "Authentication Support" section of the ntp.conf(5) page.

ntpd(8) reads its keys from a file specified using the -k command line option or the keys statement in the configuration file. While key number 0 is fixed by the NTP standard (as 56 zero bits) and may not be changed, one or more keys numbered between 1 and 65535 may be arbitrarily set in the keys file.

The key file uses the same comment conventions as the configuration file. Key entries use a fixed format of the form

keyno type key opt_IP_list

where keyno is a positive integer (between 1 and 65535), type is the message digest algorithm, key is the key itself, and opt_IP_list is an optional comma-separated list of IPs where the keyno should be trusted. that are allowed to serve time. Each IP in opt_IP_list may contain an optional /subnetbits specification which identifies the number of bits for the desired subnet of trust. If opt_IP_list is empty, any properly-authenticated message will be accepted.

The key may be given in a format controlled by the type field. The type MD5 is always supported. If ntpd was built with the OpenSSL library then any digest library supported by that library may be specified. However, if compliance with FIPS 140-2 is required the type must be either SHA or SHA1.

What follows are some key types, and corresponding formats:

MD5

The key is 1 to 16 printable characters terminated by an EOL, whitespace, or a # (which is the "start of comment" character).

SHA

SHA1

RMD160

The key is a hex-encoded ASCII string of 40 characters, which is truncated as necessary.

Note that the keys used by the ntpq(8) and ntpdc(8) programs are checked against passwords requested by the programs and entered by hand, so it is generally appropriate to specify these keys in ASCII format.

This section was generated by AutoGen, using the agtexi-cmd template and the option descriptions for the ntp.keys program. This software is released under the NTP license, <http://ntp.org/license>.

1.1.1 ntp.keys Files

/etc/ntp.keys

the default name of the configuration file

1.1.2 ntp.keys See Also

ntp.conf(5), ntpd(1ntpdmdoc), ntpdate(1ntpdatemdoc), ntpdc(1ntpdcmdoc), sntp(1sntpmdoc)

1.1.3 ntp.keys Notes

This document was derived from FreeBSD.