# NTP Symmetric Key

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# 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

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## 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`.

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### 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>.

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#### 1.1.1 ntp.keys Files

`/etc/ntp.keys`

  the default name of the configuration file

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#### 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.