This document describes the format of an NTP symmetric key file.
For a description of the use of this type of file, see the
section of the
reads its keys from a file specified using the
command line option or the
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 65534
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
is a positive integer (between 1 and 65534),
is the message digest algorithm,
is the key itself, and
is an optional comma-separated list of IPs
that are allowed to serve time.
any properly-authenticated server message will be
may be given in a format
controlled by the
is always supported.
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
must be either
What follows are some key types, and corresponding formats:
The key is 1 to 16 printable characters terminated by
(which is the "start of comment" character).
The key is a hex-encoded ASCII string of 40 characters,
which is truncated as necessary.
Note that the keys used by the
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.