ntp.keys - Network Time Protocol (NTP) authentication key file
The NTP standard specifies an extension to allow verification of the
authenticity of received NTP packets and to provide an indication of
authenticity in outgoing packets. This is implemented in xntpd using the
MD5 algorithm to compute the message-digest. The specification allows any
one of possibly 4 billion keys, numbered with 32-bit key identifiers, to be
used to authenticate an association. The servers involved in an associa-
tion must agree on the key and key identifier used to authenticate their
data, though they must each learn the key and key identifier independently.
In MD5, the keys are 64 bits (8 bytes). The xntpd daemon reads its keys
from a file specified using the -k command line option, or the keys state-
ment 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 of the keys
numbered 1 through 15 may be arbitrarily set in the keys file.
One of the keys may be chosen, by way of the configuration file requestkey
statement, to authenticate run time configuration requests made using the
xntpdc(8) program. The latter program obtains the key from the terminal as
a password, so it is generally appropriate to specify the key chosen to be
used for this purpose in ASCII format.
The NTP key file uses the same comment conventions as the configuration
file. Key entries use a fixed format of the form:
keyno type key
In this format:
Is a positive integer.
Is a single character that defines the format the key is given in.
This is always M, representing Message Digest (MD5) on Tru64 UNIX sys-
key Is the key itself. The MD5 algorithm key is a 1-to-8 character ASCII
string. Because of the simple tokenizing routine, you cannot use the
following characters in an ASCII key: " " (space), "#" (number sign),
"", "0, and " ". Note that both the keys and the authentication scheme
(MD5) must be identical between a set of peers sharing the same key
The following sample key file shows two defined NTP keys:
2 M RIrop8KPPvQvYotM # MD5 key as a random ASCII string
14 M sundial # MD5 key as an ASCII string
Conventional name of the key file
Commands: ntpdate(8), ntpq(8), xntpd(8), xntpdc(8)
Network Administration: Services