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<h1 class="settitle">Ntp-keygen User's Manual</h1>
  <div class="shortcontents">
<h2>Short Contents</h2>
<ul>
<a href="#Top">Top</a>
<a href="#Top">NTP Key Generation Program User Manual</a>
</ul>
</div>


<div class="node">
<p><hr>
<a name="Top"></a>Up:&nbsp;<a rel="up" accesskey="u" href="#dir">(dir)</a>
<br>
</div>

<h2 class="unnumbered">Top</h2>

<ul class="menu">
<li><a accesskey="1" href="#Description">Description</a>
<li><a accesskey="2" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>: 	Invoking ntp-keygen
<li><a accesskey="3" href="#Running-the-Program">Running the Program</a>
<li><a accesskey="4" href="#Random-Seed-File">Random Seed File</a>
<li><a accesskey="5" href="#Cryptographic-Data-Files">Cryptographic Data Files</a>
</ul>

<div class="node">
<p><hr>
<a name="Top"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#Description">Description</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#dir">(dir)</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#dir">(dir)</a>
<br>
</div>

<h2 class="unnumbered">NTP Key Generation Program User Manual</h2>

<p>This document describes the use of the NTP Project's <code>ntp-keygen</code>
program, that generates cryptographic data files used by the NTPv4
authentication and identity schemes.
It can generate message digest keys used in symmetric key cryptography and,
if the OpenSSL software
library has been installed, it can generate host keys, sign keys,
certificates, and identity keys and parameters used by the Autokey
public key cryptography.
The message digest keys file is generated in a
format compatible with NTPv3.
All other files are in PEM-encoded
printable ASCII format so they can be embedded as MIME attachments in
mail to other sites.

  <p>This document applies to version 4.2.7p404 of <code>ntp-keygen</code>.

<div class="node">
<p><hr>
<a name="Description"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#Running-the-Program">Running the Program</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#Top">Top</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#Top">Top</a>
<br>
</div>

<!-- node-name,  next,  previous,  up -->
<h3 class="section">Description</h3>

<p>This program generates cryptographic data files used by the NTPv4
authentication and identity schemes. It can generate message digest
keys used in symmetric key cryptography and, if the OpenSSL software
library has been installed, it can generate host keys, sign keys,
certificates, and identity keys and parameters used by the Autokey
public key cryptography. The message digest keys file is generated in a
format compatible with NTPv3. All other files are in PEM-encoded
printable ASCII format so they can be embedded as MIME attachments in
mail to other sites.

  <p>When used to generate message digest keys, the program produces a file
containing ten pseudo-random printable ASCII strings suitable for the
MD5 message digest algorithm included in the distribution.
If the
OpenSSL library is installed, it produces an additional ten hex-encoded
random bit strings suitable for the SHA1 and other message digest
algorithms.
The message digest keys file must be distributed and stored
using secure means beyond the scope of NTP itself.
Besides the keys
used for ordinary NTP associations, additional keys can be defined as
passwords for the ntpq and ntpdc utility programs.

  <p>The remaining generated files are compatible with other OpenSSL
applications and other Public Key Infrastructure (PKI) resources.
Certificates generated by this program are compatible with extant
industry practice, although some users might find the interpretation of
X509v3 extension fields somewhat liberal.
However, the identity keys
are probably not compatible with anything other than Autokey.

  <p>Some files used by this program are encrypted using a private password.
The <code>-p</code> option specifies the password for local encrypted files and the
<code>-q</code> option the password for encrypted files sent to remote sites.
If no password is specified, the host name returned by the Unix
<code>gethostname()</code> function, normally the DNS name of the host, is used.

  <p>The <kbd>pw</kbd> option of the <code>crypto</code> configuration command
specifies the read password for previously encrypted local files.
This must match the local password used by this program.
If not specified, the host name is used.
Thus, if files are generated by this program without password,
they can be read back by ntpd without password, but only on the same
host.

  <p>Normally, encrypted files for each host are generated by that host and
used only by that host, although exceptions exist as noted later on
this page.
The symmetric keys file, normally called <code>ntp.keys</code>, is
usually installed in <code>/etc</code>.
Other files and links are usually installed
in <code>/usr/local/etc</code>, which is normally in a shared filesystem in
NFS-mounted networks and cannot be changed by shared clients.
The location of the keys directory can be changed by the keysdir
configuration command in such cases.
Normally, this is in <code>/etc</code>.

  <p>This program directs commentary and error messages to the standard
error stream <code>stderr</code> and remote files to the standard output stream
<code>stdout</code> where they can be piped to other applications or redirected to
files.
The names used for generated files and links all begin with the
string <code>ntpkey</code> and include the file type,
generating host and filestamp,
as described in the <a href="#Cryptographic-Data-Files">Cryptographic Data Files</a> section below.

<div class="node">
<p><hr>
<a name="Running-the-Program"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#Random-Seed-File">Random Seed File</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#Description">Description</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#Top">Top</a>
<br>
</div>

<!-- node-name,  next,  previous,  up -->
<h3 class="section">Running the Program</h3>

<p>To test and gain experience with Autokey concepts, log in as root and
change to the keys directory, usually <code>/usr/local/etc</code>.
When run for the
first time, or if all files with names beginning <code>ntpkey</code>] have been
removed, use the <code>ntp-keygen</code> command without arguments to generate a
default RSA host key and matching RSA-MD5 certificate with expiration
date one year hence.
If run again without options, the program uses the
existing keys and parameters and generates only a new certificate with
new expiration date one year hence.

  <p>Run the command on as many hosts as necessary.
Designate one of them as the trusted host (TH) using <code>ntp-keygen</code>
with the <code>-T</code> option and configure
it to synchronize from reliable Internet servers.
Then configure the other hosts to synchronize to the TH directly or indirectly.
A certificate trail is created when Autokey asks the immediately
ascendant host towards the TH to sign its certificate, which is then
provided to the immediately descendant host on request.
All group hosts should have acyclic certificate trails ending on the TH.

  <p>The host key is used to encrypt the cookie when required and so must be
RSA type.
By default, the host key is also the sign key used to encrypt signatures.
A different sign key can be assigned using the <code>-S</code> option
and this can be either RSA or DSA type.
By default, the signature
message digest type is MD5, but any combination of sign key type and
message digest type supported by the OpenSSL library can be specified
using the <code>-c</code> option.

  <p>The rules say cryptographic media should be generated with proventic
filestamps, which means the host should already be synchronized before
this program is run.
This of course creates a chicken-and-egg problem
when the host is started for the first time.
Accordingly, the host time
should be set by some other means, such as eyeball-and-wristwatch, at
least so that the certificate lifetime is within the current year.
After that and when the host is synchronized to a proventic source, the
certificate should be re-generated.

  <p>Additional information on trusted groups and identity schemes is on the
Autokey Public-Key Authentication page.

<div class="node">
<p><hr>
<a name="ntp_002dkeygen-Invocation"></a>
<br>
</div>

<h3 class="section">Invoking ntp-keygen</h3>

<p><a name="index-ntp_002dkeygen-1"></a><a name="index-Create-a-NTP-host-key-2"></a>

  <p>This program generates cryptographic data files used by the NTPv4
authentication and identification schemes.
It generates MD5 key files used in symmetric key cryptography.
In addition, if the OpenSSL software library has been installed,
it generates keys, certificate and identity files used in public key
cryptography.
These files are used for cookie encryption,
digital signature and challenge/response identification algorithms
compatible with the Internet standard security infrastructure.

  <p>All files are in PEM-encoded printable ASCII format,
so they can be embedded as MIME attachments in mail to other sites
and certificate authorities.
By default, files are not encrypted.

  <p>When used to generate message digest keys, the program produces a file
containing ten pseudo-random printable ASCII strings suitable for the
MD5 message digest algorithm included in the distribution.
If the OpenSSL library is installed, it produces an additional ten
hex-encoded random bit strings suitable for the SHA1 and other message
digest algorithms.
The message digest keys file must be distributed and stored
using secure means beyond the scope of NTP itself.
Besides the keys used for ordinary NTP associations, additional keys
can be defined as passwords for the
<code>ntpq(1ntpqmdoc)</code>
and
<code>ntpdc(1ntpdcmdoc)</code>
utility programs.

  <p>The remaining generated files are compatible with other OpenSSL
applications and other Public Key Infrastructure (PKI) resources.
Certificates generated by this program are compatible with extant
industry practice, although some users might find the interpretation of
X509v3 extension fields somewhat liberal.
However, the identity keys are probably not compatible with anything
other than Autokey.

  <p>Some files used by this program are encrypted using a private password.
The
<code>-p</code>
option specifies the password for local encrypted files and the
<code>-q</code>
option the password for encrypted files sent to remote sites.
If no password is specified, the host name returned by the Unix
<code>gethostname()</code>
function, normally the DNS name of the host is used.

  <p>The
<kbd>pw</kbd>
option of the
<kbd>crypto</kbd>
configuration command specifies the read
password for previously encrypted local files.
This must match the local password used by this program.
If not specified, the host name is used.
Thus, if files are generated by this program without password,
they can be read back by
<kbd>ntpd</kbd>
without password but only on the same host.

  <p>Normally, encrypted files for each host are generated by that host and
used only by that host, although exceptions exist as noted later on
this page.
The symmetric keys file, normally called
<kbd>ntp.keys</kbd>,
is usually installed in
<span class="file">/etc</span>.
Other files and links are usually installed in
<span class="file">/usr/local/etc</span>,
which is normally in a shared filesystem in
NFS-mounted networks and cannot be changed by shared clients.
The location of the keys directory can be changed by the
<kbd>keysdir</kbd>
configuration command in such cases.
Normally, this is in
<span class="file">/etc</span>.

  <p>This program directs commentary and error messages to the standard
error stream
<kbd>stderr</kbd>
and remote files to the standard output stream
<kbd>stdout</kbd>
where they can be piped to other applications or redirected to files.
The names used for generated files and links all begin with the
string
<kbd>ntpkey</kbd>
and include the file type, generating host and filestamp,
as described in the
Cryptographic Data Files
section below.

<h5 class="subsubsection">Running the Program</h5>

<p>To test and gain experience with Autokey concepts, log in as root and
change to the keys directory, usually
<span class="file">/usr/local/etc</span>
When run for the first time, or if all files with names beginning with
<kbd>ntpkey</kbd>
have been removed, use the
<code>ntp-keygen</code>
command without arguments to generate a
default RSA host key and matching RSA-MD5 certificate with expiration
date one year hence.
If run again without options, the program uses the
existing keys and parameters and generates only a new certificate with
new expiration date one year hence.

  <p>Run the command on as many hosts as necessary.
Designate one of them as the trusted host (TH) using
<code>ntp-keygen</code>
with the
<code>-T</code>
option and configure it to synchronize from reliable Internet servers.
Then configure the other hosts to synchronize to the TH directly or
indirectly.
A certificate trail is created when Autokey asks the immediately
ascendant host towards the TH to sign its certificate, which is then
provided to the immediately descendant host on request.
All group hosts should have acyclic certificate trails ending on the TH.

  <p>The host key is used to encrypt the cookie when required and so must be
RSA type.
By default, the host key is also the sign key used to encrypt
signatures.
A different sign key can be assigned using the
<code>-S</code>
option and this can be either RSA or DSA type.
By default, the signature
message digest type is MD5, but any combination of sign key type and
message digest type supported by the OpenSSL library can be specified
using the
<code>-c</code>
option.
The rules say cryptographic media should be generated with proventic
filestamps, which means the host should already be synchronized before
this program is run.
This of course creates a chicken-and-egg problem
when the host is started for the first time.
Accordingly, the host time
should be set by some other means, such as eyeball-and-wristwatch, at
least so that the certificate lifetime is within the current year.
After that and when the host is synchronized to a proventic source, the
certificate should be re-generated.

  <p>Additional information on trusted groups and identity schemes is on the
Autokey Public-Key Authentication
page.

  <p>The
<code>ntpd(1ntpdmdoc)</code>
configuration command
<code>crypto</code> <code>pw</code> <kbd>password</kbd>
specifies the read password for previously encrypted files.
The daemon expires on the spot if the password is missing
or incorrect.
For convenience, if a file has been previously encrypted,
the default read password is the name of the host running
the program.
If the previous write password is specified as the host name,
these files can be read by that host with no explicit password.

  <p>File names begin with the prefix
<code>ntpkey_</code>
and end with the postfix
<kbd>_hostname.filestamp</kbd>,
where
<kbd>hostname</kbd>
is the owner name, usually the string returned
by the Unix gethostname() routine, and
<kbd>filestamp</kbd>
is the NTP seconds when the file was generated, in decimal digits.
This both guarantees uniqueness and simplifies maintenance
procedures, since all files can be quickly removed
by a
<code>rm</code> <code>ntpkey*</code>
command or all files generated
at a specific time can be removed by a
<code>rm</code>
<kbd>*filestamp</kbd>
command.
To further reduce the risk of misconfiguration,
the first two lines of a file contain the file name
and generation date and time as comments.

  <p>All files are installed by default in the keys directory
<span class="file">/usr/local/etc</span>,
which is normally in a shared filesystem
in NFS-mounted networks.
The actual location of the keys directory
and each file can be overridden by configuration commands,
but this is not recommended.
Normally, the files for each host are generated by that host
and used only by that host, although exceptions exist
as noted later on this page.

  <p>Normally, files containing private values,
including the host key, sign key and identification parameters,
are permitted root read/write-only;
while others containing public values are permitted world readable.
Alternatively, files containing private values can be encrypted
and these files permitted world readable,
which simplifies maintenance in shared file systems.
Since uniqueness is insured by the hostname and
file name extensions, the files for a NFS server and
dependent clients can all be installed in the same shared directory.

  <p>The recommended practice is to keep the file name extensions
when installing a file and to install a soft link
from the generic names specified elsewhere on this page
to the generated files.
This allows new file generations to be activated simply
by changing the link.
If a link is present, ntpd follows it to the file name
to extract the filestamp.
If a link is not present,
<code>ntpd(1ntpdmdoc)</code>
extracts the filestamp from the file itself.
This allows clients to verify that the file and generation times
are always current.
The
<code>ntp-keygen</code>
program uses the same timestamp extension for all files generated
at one time, so each generation is distinct and can be readily
recognized in monitoring data.

<h5 class="subsubsection">Running the program</h5>

<p>The safest way to run the
<code>ntp-keygen</code>
program is logged in directly as root.
The recommended procedure is change to the keys directory,
usually
<span class="file">/usr/local/etc</span>,
then run the program.
When run for the first time,
or if all
<code>ntpkey</code>
files have been removed,
the program generates a RSA host key file and matching RSA-MD5 certificate file,
which is all that is necessary in many cases.
The program also generates soft links from the generic names
to the respective files.
If run again, the program uses the same host key file,
but generates a new certificate file and link.

  <p>The host key is used to encrypt the cookie when required and so must be RSA type.
By default, the host key is also the sign key used to encrypt signatures.
When necessary, a different sign key can be specified and this can be
either RSA or DSA type.
By default, the message digest type is MD5, but any combination
of sign key type and message digest type supported by the OpenSSL library
can be specified, including those using the MD2, MD5, SHA, SHA1, MDC2
and RIPE160 message digest algorithms.
However, the scheme specified in the certificate must be compatible
with the sign key.
Certificates using any digest algorithm are compatible with RSA sign keys;
however, only SHA and SHA1 certificates are compatible with DSA sign keys.

  <p>Private/public key files and certificates are compatible with
other OpenSSL applications and very likely other libraries as well.
Certificates or certificate requests derived from them should be compatible
with extant industry practice, although some users might find
the interpretation of X509v3 extension fields somewhat liberal.
However, the identification parameter files, although encoded
as the other files, are probably not compatible with anything other than Autokey.

  <p>Running the program as other than root and using the Unix
<code>su</code>
command
to assume root may not work properly, since by default the OpenSSL library
looks for the random seed file
<code>.rnd</code>
in the user home directory.
However, there should be only one
<code>.rnd</code>,
most conveniently
in the root directory, so it is convenient to define the
<code>$RANDFILE</code>
environment variable used by the OpenSSL library as the path to
<code>/.rnd</code>.

  <p>Installing the keys as root might not work in NFS-mounted
shared file systems, as NFS clients may not be able to write
to the shared keys directory, even as root.
In this case, NFS clients can specify the files in another
directory such as
<span class="file">/etc</span>
using the
<code>keysdir</code>
command.
There is no need for one client to read the keys and certificates
of other clients or servers, as these data are obtained automatically
by the Autokey protocol.

  <p>Ordinarily, cryptographic files are generated by the host that uses them,
but it is possible for a trusted agent (TA) to generate these files
for other hosts; however, in such cases files should always be encrypted.
The subject name and trusted name default to the hostname
of the host generating the files, but can be changed by command line options.
It is convenient to designate the owner name and trusted name
as the subject and issuer fields, respectively, of the certificate.
The owner name is also used for the host and sign key files,
while the trusted name is used for the identity files.

  <p>All files are installed by default in the keys directory
<span class="file">/usr/local/etc</span>,
which is normally in a shared filesystem
in NFS-mounted networks.
The actual location of the keys directory
and each file can be overridden by configuration commands,
but this is not recommended.
Normally, the files for each host are generated by that host
and used only by that host, although exceptions exist
as noted later on this page.

  <p>Normally, files containing private values,
including the host key, sign key and identification parameters,
are permitted root read/write-only;
while others containing public values are permitted world readable.
Alternatively, files containing private values can be encrypted
and these files permitted world readable,
which simplifies maintenance in shared file systems.
Since uniqueness is insured by the hostname and
file name extensions, the files for a NFS server and
dependent clients can all be installed in the same shared directory.

  <p>The recommended practice is to keep the file name extensions
when installing a file and to install a soft link
from the generic names specified elsewhere on this page
to the generated files.
This allows new file generations to be activated simply
by changing the link.
If a link is present, ntpd follows it to the file name
to extract the filestamp.
If a link is not present,
<code>ntpd(1ntpdmdoc)</code>
extracts the filestamp from the file itself.
This allows clients to verify that the file and generation times
are always current.
The
<code>ntp-keygen</code>
program uses the same timestamp extension for all files generated
at one time, so each generation is distinct and can be readily
recognized in monitoring data.

<h5 class="subsubsection">Running the program</h5>

<p>The safest way to run the
<code>ntp-keygen</code>
program is logged in directly as root.
The recommended procedure is change to the keys directory,
usually
<span class="file">/usr/local/etc</span>,
then run the program.
When run for the first time,
or if all
<code>ntpkey</code>
files have been removed,
the program generates a RSA host key file and matching RSA-MD5 certificate file,
which is all that is necessary in many cases.
The program also generates soft links from the generic names
to the respective files.
If run again, the program uses the same host key file,
but generates a new certificate file and link.

  <p>The host key is used to encrypt the cookie when required and so must be RSA type.
By default, the host key is also the sign key used to encrypt signatures.
When necessary, a different sign key can be specified and this can be
either RSA or DSA type.
By default, the message digest type is MD5, but any combination
of sign key type and message digest type supported by the OpenSSL library
can be specified, including those using the MD2, MD5, SHA, SHA1, MDC2
and RIPE160 message digest algorithms.
However, the scheme specified in the certificate must be compatible
with the sign key.
Certificates using any digest algorithm are compatible with RSA sign keys;
however, only SHA and SHA1 certificates are compatible with DSA sign keys.

  <p>Private/public key files and certificates are compatible with
other OpenSSL applications and very likely other libraries as well.
Certificates or certificate requests derived from them should be compatible
with extant industry practice, although some users might find
the interpretation of X509v3 extension fields somewhat liberal.
However, the identification parameter files, although encoded
as the other files, are probably not compatible with anything other than Autokey.

  <p>Running the program as other than root and using the Unix
<code>su</code>
command
to assume root may not work properly, since by default the OpenSSL library
looks for the random seed file
<code>.rnd</code>
in the user home directory.
However, there should be only one
<code>.rnd</code>,
most conveniently
in the root directory, so it is convenient to define the
<code>$RANDFILE</code>
environment variable used by the OpenSSL library as the path to
<code>/.rnd</code>.

  <p>Installing the keys as root might not work in NFS-mounted
shared file systems, as NFS clients may not be able to write
to the shared keys directory, even as root.
In this case, NFS clients can specify the files in another
directory such as
<span class="file">/etc</span>
using the
<code>keysdir</code>
command.
There is no need for one client to read the keys and certificates
of other clients or servers, as these data are obtained automatically
by the Autokey protocol.

  <p>Ordinarily, cryptographic files are generated by the host that uses them,
but it is possible for a trusted agent (TA) to generate these files
for other hosts; however, in such cases files should always be encrypted.
The subject name and trusted name default to the hostname
of the host generating the files, but can be changed by command line options.
It is convenient to designate the owner name and trusted name
as the subject and issuer fields, respectively, of the certificate.
The owner name is also used for the host and sign key files,
while the trusted name is used for the identity files.
seconds.
seconds.

  <p>s Trusted Hosts and Groups
Each cryptographic configuration involves selection of a signature scheme
and identification scheme, called a cryptotype,
as explained in the
<a href="#Authentication-Options">Authentication Options</a>
section of
<code>ntp.conf(5)</code>.
The default cryptotype uses RSA encryption, MD5 message digest
and TC identification.
First, configure a NTP subnet including one or more low-stratum
trusted hosts from which all other hosts derive synchronization
directly or indirectly.
Trusted hosts have trusted certificates;
all other hosts have nontrusted certificates.
These hosts will automatically and dynamically build authoritative
certificate trails to one or more trusted hosts.
A trusted group is the set of all hosts that have, directly or indirectly,
a certificate trail ending at a trusted host.
The trail is defined by static configuration file entries
or dynamic means described on the
<a href="#Automatic-NTP-Configuration-Options">Automatic NTP Configuration Options</a>
section of
<code>ntp.conf(5)</code>.

  <p>On each trusted host as root, change to the keys directory.
To insure a fresh fileset, remove all
<code>ntpkey</code>
files.
Then run
<code>ntp-keygen</code>
<code>-T</code>
to generate keys and a trusted certificate.
On all other hosts do the same, but leave off the
<code>-T</code>
flag to generate keys and nontrusted certificates.
When complete, start the NTP daemons beginning at the lowest stratum
and working up the tree.
It may take some time for Autokey to instantiate the certificate trails
throughout the subnet, but setting up the environment is completely automatic.

  <p>If it is necessary to use a different sign key or different digest/signature
scheme than the default, run
<code>ntp-keygen</code>
with the
<code>-S</code> <kbd>type</kbd>
option, where
<kbd>type</kbd>
is either
<code>RSA</code>
or
<code>DSA</code>.
The most often need to do this is when a DSA-signed certificate is used.
If it is necessary to use a different certificate scheme than the default,
run
<code>ntp-keygen</code>
with the
<code>-c</code> <kbd>scheme</kbd>
option and selected
<kbd>scheme</kbd>
as needed.
f
<code>ntp-keygen</code>
is run again without these options, it generates a new certificate
using the same scheme and sign key.

  <p>After setting up the environment it is advisable to update certificates
from time to time, if only to extend the validity interval.
Simply run
<code>ntp-keygen</code>
with the same flags as before to generate new certificates
using existing keys.
However, if the host or sign key is changed,
<code>ntpd(1ntpdmdoc)</code>
should be restarted.
When
<code>ntpd(1ntpdmdoc)</code>
is restarted, it loads any new files and restarts the protocol.
Other dependent hosts will continue as usual until signatures are refreshed,
at which time the protocol is restarted.

<h5 class="subsubsection">Identity Schemes</h5>

<p>As mentioned on the Autonomous Authentication page,
the default TC identity scheme is vulnerable to a middleman attack.
However, there are more secure identity schemes available,
including PC, IFF, GQ and MV described on the
"Identification Schemes"
page
(maybe available at
<code>http://www.eecis.udel.edu/%7emills/keygen.html</code>).
These schemes are based on a TA, one or more trusted hosts
and some number of nontrusted hosts.
Trusted hosts prove identity using values provided by the TA,
while the remaining hosts prove identity using values provided
by a trusted host and certificate trails that end on that host.
The name of a trusted host is also the name of its sugroup
and also the subject and issuer name on its trusted certificate.
The TA is not necessarily a trusted host in this sense, but often is.

  <p>In some schemes there are separate keys for servers and clients.
A server can also be a client of another server,
but a client can never be a server for another client.
In general, trusted hosts and nontrusted hosts that operate
as both server and client have parameter files that contain
both server and client keys.
Hosts that operate
only as clients have key files that contain only client keys.

  <p>The PC scheme supports only one trusted host in the group.
On trusted host alice run
<code>ntp-keygen</code>
<code>-P</code>
<code>-p</code> <kbd>password</kbd>
to generate the host key file
<span class="file">ntpkey_RSAkey_</span><kbd>alice.filestamp</kbd>
and trusted private certificate file
<span class="file">ntpkey_RSA-MD5_cert_</span><kbd>alice.filestamp</kbd>.
Copy both files to all group hosts;
they replace the files which would be generated in other schemes.
On each host bob install a soft link from the generic name
<span class="file">ntpkey_host_</span><kbd>bob</kbd>
to the host key file and soft link
<span class="file">ntpkey_cert_</span><kbd>bob</kbd>
to the private certificate file.
Note the generic links are on bob, but point to files generated
by trusted host alice.
In this scheme it is not possible to refresh
either the keys or certificates without copying them
to all other hosts in the group.

  <p>For the IFF scheme proceed as in the TC scheme to generate keys
and certificates for all group hosts, then for every trusted host in the group,
generate the IFF parameter file.
On trusted host alice run
<code>ntp-keygen</code>
<code>-T</code>
<code>-I</code>
<code>-p</code> <kbd>password</kbd>
to produce her parameter file
<span class="file">ntpkey_IFFpar_</span><kbd>alice.filestamp</kbd>,
which includes both server and client keys.
Copy this file to all group hosts that operate as both servers
and clients and install a soft link from the generic
<span class="file">ntpkey_iff_</span><kbd>alice</kbd>
to this file.
If there are no hosts restricted to operate only as clients,
there is nothing further to do.
As the IFF scheme is independent
of keys and certificates, these files can be refreshed as needed.

  <p>If a rogue client has the parameter file, it could masquerade
as a legitimate server and present a middleman threat.
To eliminate this threat, the client keys can be extracted
from the parameter file and distributed to all restricted clients.
After generating the parameter file, on alice run
<code>ntp-keygen</code>
<code>-e</code>
and pipe the output to a file or mail program.
Copy or mail this file to all restricted clients.
On these clients install a soft link from the generic
<span class="file">ntpkey_iff_</span><kbd>alice</kbd>
to this file.
To further protect the integrity of the keys,
each file can be encrypted with a secret password.

  <p>For the GQ scheme proceed as in the TC scheme to generate keys
and certificates for all group hosts, then for every trusted host
in the group, generate the IFF parameter file.
On trusted host alice run
<code>ntp-keygen</code>
<code>-T</code>
<code>-G</code>
<code>-p</code> <kbd>password</kbd>
to produce her parameter file
<span class="file">ntpkey_GQpar_</span><kbd>alice.filestamp</kbd>,
which includes both server and client keys.
Copy this file to all group hosts and install a soft link
from the generic
<span class="file">ntpkey_gq_</span><kbd>alice</kbd>
to this file.
In addition, on each host bob install a soft link
from generic
<span class="file">ntpkey_gq_</span><kbd>bob</kbd>
to this file.
As the GQ scheme updates the GQ parameters file and certificate
at the same time, keys and certificates can be regenerated as needed.

  <p>For the MV scheme, proceed as in the TC scheme to generate keys
and certificates for all group hosts.
For illustration assume trish is the TA, alice one of several trusted hosts
and bob one of her clients.
On TA trish run
<code>ntp-keygen</code>
<code>-V</code> <kbd>n</kbd>
<code>-p</code> <kbd>password</kbd>,
where
<kbd>n</kbd>
is the number of revokable keys (typically 5) to produce
the parameter file
<span class="file">ntpkeys_MVpar_</span><kbd>trish.filestamp</kbd>
and client key files
<span class="file">ntpkeys_MVkeyd_</span><kbd>trish.filestamp</kbd>
where
<kbd>d</kbd>
is the key number (0 &lt;
<kbd>d</kbd>
&lt;
<kbd>n</kbd>).
Copy the parameter file to alice and install a soft link
from the generic
<span class="file">ntpkey_mv_</span><kbd>alice</kbd>
to this file.
Copy one of the client key files to alice for later distribution
to her clients.
It doesn't matter which client key file goes to alice,
since they all work the same way.
Alice copies the client key file to all of her cliens.
On client bob install a soft link from generic
<span class="file">ntpkey_mvkey_</span><kbd>bob</kbd>
to the client key file.
As the MV scheme is independent of keys and certificates,
these files can be refreshed as needed.

<h5 class="subsubsection">Command Line Options</h5>

     <dl>
<dt><code>-c</code> <kbd>scheme</kbd><dd>Select certificate message digest/signature encryption scheme.
The
<kbd>scheme</kbd>
can be one of the following:
. Cm RSA-MD2 , RSA-MD5 , RSA-SHA , RSA-SHA1 , RSA-MDC2 , RSA-RIPEMD160 , DSA-SHA ,
or
<code>DSA-SHA1</code>.
Note that RSA schemes must be used with a RSA sign key and DSA
schemes must be used with a DSA sign key.
The default without this option is
<code>RSA-MD5</code>.
<br><dt><code>-d</code><dd>Enable debugging.
This option displays the cryptographic data produced in eye-friendly billboards.
<br><dt><code>-e</code><dd>Write the IFF client keys to the standard output.
This is intended for automatic key distribution by mail.
<br><dt><code>-G</code><dd>Generate parameters and keys for the GQ identification scheme,
obsoleting any that may exist.
<br><dt><code>-g</code><dd>Generate keys for the GQ identification scheme
using the existing GQ parameters.
If the GQ parameters do not yet exist, create them first.
<br><dt><code>-H</code><dd>Generate new host keys, obsoleting any that may exist.
<br><dt><code>-I</code><dd>Generate parameters for the IFF identification scheme,
obsoleting any that may exist.
<br><dt><code>-i</code> <kbd>name</kbd><dd>Set the suject name to
<kbd>name</kbd>.
This is used as the subject field in certificates
and in the file name for host and sign keys.
<br><dt><code>-M</code><dd>Generate MD5 keys, obsoleting any that may exist.
<br><dt><code>-P</code><dd>Generate a private certificate.
By default, the program generates public certificates.
<br><dt><code>-p</code> <kbd>password</kbd><dd>Encrypt generated files containing private data with
<kbd>password</kbd>
and the DES-CBC algorithm.
<br><dt><code>-q</code><dd>Set the password for reading files to password.
<br><dt><code>-S</code> <code>[RSA | DSA]</code><dd>Generate a new sign key of the designated type,
obsoleting any that may exist.
By default, the program uses the host key as the sign key.
<br><dt><code>-s</code> <kbd>name</kbd><dd>Set the issuer name to
<kbd>name</kbd>.
This is used for the issuer field in certificates
and in the file name for identity files.
<br><dt><code>-T</code><dd>Generate a trusted certificate.
By default, the program generates a non-trusted certificate.
<br><dt><code>-V</code> <kbd>nkeys</kbd><dd>Generate parameters and keys for the Mu-Varadharajan (MV) identification scheme.
</dl>

<h5 class="subsubsection">Random Seed File</h5>

<p>All cryptographically sound key generation schemes must have means
to randomize the entropy seed used to initialize
the internal pseudo-random number generator used
by the library routines.
The OpenSSL library uses a designated random seed file for this purpose.
The file must be available when starting the NTP daemon and
<code>ntp-keygen</code>
program.
If a site supports OpenSSL or its companion OpenSSH,
it is very likely that means to do this are already available.

  <p>It is important to understand that entropy must be evolved
for each generation, for otherwise the random number sequence
would be predictable.
Various means dependent on external events, such as keystroke intervals,
can be used to do this and some systems have built-in entropy sources.
Suitable means are described in the OpenSSL software documentation,
but are outside the scope of this page.

  <p>The entropy seed used by the OpenSSL library is contained in a file,
usually called
<code>.rnd</code>,
which must be available when starting the NTP daemon
or the
<code>ntp-keygen</code>
program.
The NTP daemon will first look for the file
using the path specified by the
<code>randfile</code>
subcommand of the
<code>crypto</code>
configuration command.
If not specified in this way, or when starting the
<code>ntp-keygen</code>
program,
the OpenSSL library will look for the file using the path specified
by the
.Ev RANDFILE
environment variable in the user home directory,
whether root or some other user.
If the
.Ev RANDFILE
environment variable is not present,
the library will look for the
<code>.rnd</code>
file in the user home directory.
If the file is not available or cannot be written,
the daemon exits with a message to the system log and the program
exits with a suitable error message.

<h5 class="subsubsection">Cryptographic Data Files</h5>

<p>All other file formats begin with two lines.
The first contains the file name, including the generated host name
and filestamp.
The second contains the datestamp in conventional Unix date format.
Lines beginning with # are considered comments and ignored by the
<code>ntp-keygen</code>
program and
<code>ntpd(1ntpdmdoc)</code>
daemon.
Cryptographic values are encoded first using ASN.1 rules,
then encrypted if necessary, and finally written PEM-encoded
printable ASCII format preceded and followed by MIME content identifier lines.

  <p>The format of the symmetric keys file is somewhat different
than the other files in the interest of backward compatibility.
Since DES-CBC is deprecated in NTPv4, the only key format of interest
is MD5 alphanumeric strings.
Following hte heard the keys are
entered one per line in the format
<pre class="example">     <kbd>keyno</kbd> <kbd>type</kbd> <kbd>key</kbd>
</pre>
  <p>where
<kbd>keyno</kbd>
is a positive integer in the range 1-65,535,
<kbd>type</kbd>
is the string MD5 defining the key format and
<kbd>key</kbd>
is the key itself,
which is a printable ASCII string 16 characters or less in length.
Each character is chosen from the 93 printable characters
in the range 0x21 through 0x7f excluding space and the
#
character.

  <p>Note that the keys used by the
<code>ntpq(1ntpqmdoc)</code>
and
<code>ntpdc(1ntpdcmdoc)</code>
programs
are checked against passwords requested by the programs
and entered by hand, so it is generally appropriate to specify these keys
in human readable ASCII format.

  <p>The
<code>ntp-keygen</code>
program generates a MD5 symmetric keys file
<span class="file">ntpkey_MD5key_</span><kbd>hostname.filestamp</kbd>.
Since the file contains private shared keys,
it should be visible only to root and distributed by secure means
to other subnet hosts.
The NTP daemon loads the file
<span class="file">ntp.keys</span>,
so
<code>ntp-keygen</code>
installs a soft link from this name to the generated file.
Subsequently, similar soft links must be installed by manual
or automated means on the other subnet hosts.
While this file is not used with the Autokey Version 2 protocol,
it is needed to authenticate some remote configuration commands
used by the
<code>ntpq(1ntpqmdoc)</code>
and
<code>ntpdc(1ntpdcmdoc)</code>
utilities.

  <p>This section was generated by <strong>AutoGen</strong>,
using the <code>agtexi-cmd</code> template and the option descriptions for the <code>ntp-keygen</code> program.
This software is released under the NTP license, &lt;http://ntp.org/license&gt;.

<ul class="menu">
<li><a accesskey="1" href="#ntp_002dkeygen-usage">ntp-keygen usage</a>:                   ntp-keygen help/usage (<span class="option">--help</span>)
<li><a accesskey="2" href="#ntp_002dkeygen-imbits">ntp-keygen imbits</a>:                  imbits option (-b)
<li><a accesskey="3" href="#ntp_002dkeygen-certificate">ntp-keygen certificate</a>:             certificate option (-c)
<li><a accesskey="4" href="#ntp_002dkeygen-cipher">ntp-keygen cipher</a>:                  cipher option (-C)
<li><a accesskey="5" href="#ntp_002dkeygen-id_002dkey">ntp-keygen id-key</a>:                  id-key option (-e)
<li><a accesskey="6" href="#ntp_002dkeygen-gq_002dparams">ntp-keygen gq-params</a>:               gq-params option (-G)
<li><a accesskey="7" href="#ntp_002dkeygen-host_002dkey">ntp-keygen host-key</a>:                host-key option (-H)
<li><a accesskey="8" href="#ntp_002dkeygen-iffkey">ntp-keygen iffkey</a>:                  iffkey option (-I)
<li><a accesskey="9" href="#ntp_002dkeygen-ident">ntp-keygen ident</a>:                   ident option (-i)
<li><a href="#ntp_002dkeygen-lifetime">ntp-keygen lifetime</a>:                lifetime option (-l)
<li><a href="#ntp_002dkeygen-md5key">ntp-keygen md5key</a>:                  md5key option (-M)
<li><a href="#ntp_002dkeygen-modulus">ntp-keygen modulus</a>:                 modulus option (-m)
<li><a href="#ntp_002dkeygen-pvt_002dcert">ntp-keygen pvt-cert</a>:                pvt-cert option (-P)
<li><a href="#ntp_002dkeygen-pvt_002dpasswd">ntp-keygen pvt-passwd</a>:              pvt-passwd option (-p)
<li><a href="#ntp_002dkeygen-get_002dpvt_002dpasswd">ntp-keygen get-pvt-passwd</a>:          get-pvt-passwd option (-q)
<li><a href="#ntp_002dkeygen-sign_002dkey">ntp-keygen sign-key</a>:                sign-key option (-S)
<li><a href="#ntp_002dkeygen-subject_002dname">ntp-keygen subject-name</a>:            subject-name option (-s)
<li><a href="#ntp_002dkeygen-trusted_002dcert">ntp-keygen trusted-cert</a>:            trusted-cert option (-T)
<li><a href="#ntp_002dkeygen-mv_002dparams">ntp-keygen mv-params</a>:               mv-params option (-V)
<li><a href="#ntp_002dkeygen-mv_002dkeys">ntp-keygen mv-keys</a>:                 mv-keys option (-v)
<li><a href="#ntp_002dkeygen-config">ntp-keygen config</a>:                  presetting/configuring ntp-keygen
<li><a href="#ntp_002dkeygen-exit-status">ntp-keygen exit status</a>:             exit status
<li><a href="#ntp_002dkeygen-Usage">ntp-keygen Usage</a>:                   Usage
<li><a href="#ntp_002dkeygen-Notes">ntp-keygen Notes</a>:                   Notes
<li><a href="#ntp_002dkeygen-Bugs">ntp-keygen Bugs</a>:                    Bugs
</ul>

<div class="node">
<p><hr>
<a name="ntp_002dkeygen-usage"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-imbits">ntp-keygen imbits</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">ntp-keygen help/usage (<span class="option">--help</span>)</h4>

<p><a name="index-ntp_002dkeygen-help-3"></a>
This is the automatically generated usage text for ntp-keygen.

  <p>The text printed is the same whether selected with the <code>help</code> option
(<span class="option">--help</span>) or the <code>more-help</code> option (<span class="option">--more-help</span>).  <code>more-help</code> will print
the usage text by passing it through a pager program.
<code>more-help</code> is disabled on platforms without a working
<code>fork(2)</code> function.  The <code>PAGER</code> environment variable is
used to select the program, defaulting to <span class="file">more</span>.  Both will exit
with a status code of 0.

<pre class="example">ntp-keygen (ntp) - Create a NTP host key - Ver. 4.2.7p403
Usage:  ntp-keygen [ -&lt;flag&gt; [&lt;val&gt;] | --&lt;name&gt;[{=| }&lt;val&gt;] ]...
  Flg Arg Option-Name    Description
   -b Num imbits         identity modulus bits
                                - it must be in the range:
                                  256 to 2048
   -c Str certificate    certificate scheme
   -C Str cipher         privatekey cipher
   -d no  debug-level    Increase debug verbosity level
                                - may appear multiple times
   -D Num set-debug-level Set the debug verbosity level
                                - may appear multiple times
   -e no  id-key         Write IFF or GQ identity keys
   -G no  gq-params      Generate GQ parameters and keys
   -H no  host-key       generate RSA host key
   -I no  iffkey         generate IFF parameters
   -i Str ident          set Autokey group name
   -l Num lifetime       set certificate lifetime
   -M no  md5key         generate MD5 keys
   -m Num modulus        modulus
                                - it must be in the range:
                                  256 to 2048
   -P no  pvt-cert       generate PC private certificate
   -p Str pvt-passwd     output private password
   -q Str get-pvt-passwd input private password
   -S Str sign-key       generate sign key (RSA or DSA)
   -s Str subject-name   set host and optionally group name
   -T no  trusted-cert   trusted certificate (TC scheme)
   -V Num mv-params      generate &lt;num&gt; MV parameters
   -v Num mv-keys        update &lt;num&gt; MV keys
      opt version        output version information and exit
   -? no  help           display extended usage information and exit
   -! no  more-help      extended usage information passed thru pager
   -&gt; opt save-opts      save the option state to a config file
   -&lt; Str load-opts      load options from a config file
                                - disabled as '--no-load-opts'
                                - may appear multiple times

Options are specified by doubled hyphens and their name or by a single
hyphen and the flag character.


The following option preset mechanisms are supported:
 - reading file $HOME/.ntprc
 - reading file ./.ntprc
 - examining environment variables named NTP_KEYGEN_*

Please send bug reports to:  &lt;http://bugs.ntp.org, bugs@ntp.org&gt;

exit 0
</pre>
  <div class="node">
<p><hr>
<a name="ntp_002dkeygen-imbits"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-certificate">ntp-keygen certificate</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-usage">ntp-keygen usage</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">imbits option (-b)</h4>

<p><a name="index-ntp_002dkeygen_002dimbits-4"></a>
This is the &ldquo;identity modulus bits&rdquo; option.
This option takes a number argument <span class="file">imbits</span>.

<p class="noindent">This option has some usage constraints.  It:
     <ul>
<li>must be compiled in by defining <code>AUTOKEY</code> during the compilation.
</ul>

  <p>The number of bits in the identity modulus.  The default is 256.
<div class="node">
<p><hr>
<a name="ntp_002dkeygen-certificate"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-cipher">ntp-keygen cipher</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-imbits">ntp-keygen imbits</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">certificate option (-c)</h4>

<p><a name="index-ntp_002dkeygen_002dcertificate-5"></a>
This is the &ldquo;certificate scheme&rdquo; option.
This option takes a string argument <span class="file">scheme</span>.

<p class="noindent">This option has some usage constraints.  It:
     <ul>
<li>must be compiled in by defining <code>AUTOKEY</code> during the compilation.
</ul>

  <p>scheme is one of
RSA-MD2, RSA-MD5, RSA-SHA, RSA-SHA1, RSA-MDC2, RSA-RIPEMD160,
DSA-SHA, or DSA-SHA1.

  <p>Select the certificate message digest/signature encryption scheme.
Note that RSA schemes must be used with a RSA sign key and DSA
schemes must be used with a DSA sign key.  The default without
this option is RSA-MD5.
<div class="node">
<p><hr>
<a name="ntp_002dkeygen-cipher"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-id_002dkey">ntp-keygen id-key</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-certificate">ntp-keygen certificate</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">cipher option (-C)</h4>

<p><a name="index-ntp_002dkeygen_002dcipher-6"></a>
This is the &ldquo;privatekey cipher&rdquo; option.
This option takes a string argument <span class="file">cipher</span>.

<p class="noindent">This option has some usage constraints.  It:
     <ul>
<li>must be compiled in by defining <code>AUTOKEY</code> during the compilation.
</ul>

  <p>Select the cipher which is used to encrypt the files containing
private keys.  The default is three-key triple DES in CBC mode,
equivalent to "<code>-C des-ede3-cbc".  The openssl tool lists ciphers
available in "openssl -h" output.
</code><div class="node">
<p><hr>
<a name="ntp_002dkeygen-id_002dkey"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-gq_002dparams">ntp-keygen gq-params</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-cipher">ntp-keygen cipher</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">id-key option (-e)</h4>

<p><a name="index-ntp_002dkeygen_002did_002dkey-7"></a>
This is the &ldquo;write iff or gq identity keys&rdquo; option.

<p class="noindent">This option has some usage constraints.  It:
     <ul>
<li>must be compiled in by defining <code>AUTOKEY</code> during the compilation.
</ul>

  <p>Write the IFF or GQ client keys to the standard output.  This is
intended for automatic key distribution by mail.
<div class="node">
<p><hr>
<a name="ntp_002dkeygen-gq_002dparams"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-host_002dkey">ntp-keygen host-key</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-id_002dkey">ntp-keygen id-key</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">gq-params option (-G)</h4>

<p><a name="index-ntp_002dkeygen_002dgq_002dparams-8"></a>
This is the &ldquo;generate gq parameters and keys&rdquo; option.

<p class="noindent">This option has some usage constraints.  It:
     <ul>
<li>must be compiled in by defining <code>AUTOKEY</code> during the compilation.
</ul>

  <p>Generate parameters and keys for the GQ identification scheme,
obsoleting any that may exist.
<div class="node">
<p><hr>
<a name="ntp_002dkeygen-host_002dkey"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-iffkey">ntp-keygen iffkey</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-gq_002dparams">ntp-keygen gq-params</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">host-key option (-H)</h4>

<p><a name="index-ntp_002dkeygen_002dhost_002dkey-9"></a>
This is the &ldquo;generate rsa host key&rdquo; option.

<p class="noindent">This option has some usage constraints.  It:
     <ul>
<li>must be compiled in by defining <code>AUTOKEY</code> during the compilation.
</ul>

  <p>Generate new host keys, obsoleting any that may exist.
<div class="node">
<p><hr>
<a name="ntp_002dkeygen-iffkey"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-ident">ntp-keygen ident</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-host_002dkey">ntp-keygen host-key</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">iffkey option (-I)</h4>

<p><a name="index-ntp_002dkeygen_002diffkey-10"></a>
This is the &ldquo;generate iff parameters&rdquo; option.

<p class="noindent">This option has some usage constraints.  It:
     <ul>
<li>must be compiled in by defining <code>AUTOKEY</code> during the compilation.
</ul>

  <p>Generate parameters for the IFF identification scheme, obsoleting
any that may exist.
<div class="node">
<p><hr>
<a name="ntp_002dkeygen-ident"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-lifetime">ntp-keygen lifetime</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-iffkey">ntp-keygen iffkey</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">ident option (-i)</h4>

<p><a name="index-ntp_002dkeygen_002dident-11"></a>
This is the &ldquo;set autokey group name&rdquo; option.
This option takes a string argument <span class="file">group</span>.

<p class="noindent">This option has some usage constraints.  It:
     <ul>
<li>must be compiled in by defining <code>AUTOKEY</code> during the compilation.
</ul>

  <p>Set the optional Autokey group name to name.  This is used in
the file name of IFF, GQ, and MV client parameters files.  In
that role, the default is the host name if this option is not
provided.  The group name, if specified using <code>-i/--ident</code> or
using <code>-s/--subject-name</code> following an '<code>}' character,
is also a part of the self-signed host certificate's subject and
issuer names in the form host
  <p>'crypto ident' or 'server ident' configuration in
ntpd's configuration file.
</code><div class="node">
<p><hr>
<a name="ntp_002dkeygen-lifetime"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-md5key">ntp-keygen md5key</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-ident">ntp-keygen ident</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">lifetime option (-l)</h4>

<p><a name="index-ntp_002dkeygen_002dlifetime-12"></a>
This is the ``set certificate lifetime'' option.
This option takes a number argument <span class="file">lifetime</span>.

<p class="noindent">This option has some usage constraints.  It:
     <ul>
<li>must be compiled in by defining <code>AUTOKEY</code> during the compilation.
</ul>

  <p>Set the certificate expiration to lifetime days from now.
<div class="node">
<p><hr>
<a name="ntp_002dkeygen-md5key"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-modulus">ntp-keygen modulus</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-lifetime">ntp-keygen lifetime</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">md5key option (-M)</h4>

<p><a name="index-ntp_002dkeygen_002dmd5key-13"></a>
This is the ``generate md5 keys'' option.
Generate MD5 keys, obsoleting any that may exist.
<div class="node">
<p><hr>
<a name="ntp_002dkeygen-modulus"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-pvt_002dcert">ntp-keygen pvt-cert</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-md5key">ntp-keygen md5key</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">modulus option (-m)</h4>

<p><a name="index-ntp_002dkeygen_002dmodulus-14"></a>
This is the ``modulus'' option.
This option takes a number argument <span class="file">modulus</span>.

<p class="noindent">This option has some usage constraints.  It:
     <ul>
<li>must be compiled in by defining <code>AUTOKEY</code> during the compilation.
</ul>

  <p>The number of bits in the prime modulus.  The default is 512.
<div class="node">
<p><hr>
<a name="ntp_002dkeygen-pvt_002dcert"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-pvt_002dpasswd">ntp-keygen pvt-passwd</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-modulus">ntp-keygen modulus</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">pvt-cert option (-P)</h4>

<p><a name="index-ntp_002dkeygen_002dpvt_002dcert-15"></a>
This is the ``generate pc private certificate'' option.

<p class="noindent">This option has some usage constraints.  It:
     <ul>
<li>must be compiled in by defining <code>AUTOKEY</code> during the compilation.
</ul>

  <p>Generate a private certificate.  By default, the program generates
public certificates.
<div class="node">
<p><hr>
<a name="ntp_002dkeygen-pvt_002dpasswd"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-get_002dpvt_002dpasswd">ntp-keygen get-pvt-passwd</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-pvt_002dcert">ntp-keygen pvt-cert</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">pvt-passwd option (-p)</h4>

<p><a name="index-ntp_002dkeygen_002dpvt_002dpasswd-16"></a>
This is the ``output private password'' option.
This option takes a string argument <span class="file">passwd</span>.

<p class="noindent">This option has some usage constraints.  It:
     <ul>
<li>must be compiled in by defining <code>AUTOKEY</code> during the compilation.
</ul>

  <p>Encrypt generated files containing private data with the specified
password and the cipher selected with <code>-C/--cipher</code>.
<div class="node">
<p><hr>
<a name="ntp_002dkeygen-get_002dpvt_002dpasswd"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-sign_002dkey">ntp-keygen sign-key</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-pvt_002dpasswd">ntp-keygen pvt-passwd</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">get-pvt-passwd option (-q)</h4>

<p><a name="index-ntp_002dkeygen_002dget_002dpvt_002dpasswd-17"></a>
This is the ``input private password'' option.
This option takes a string argument <span class="file">passwd</span>.

<p class="noindent">This option has some usage constraints.  It:
     <ul>
<li>must be compiled in by defining <code>AUTOKEY</code> during the compilation.
</ul>

  <p>Set the password for reading files to the specified password.
<div class="node">
<p><hr>
<a name="ntp_002dkeygen-sign_002dkey"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-subject_002dname">ntp-keygen subject-name</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-get_002dpvt_002dpasswd">ntp-keygen get-pvt-passwd</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">sign-key option (-S)</h4>

<p><a name="index-ntp_002dkeygen_002dsign_002dkey-18"></a>
This is the ``generate sign key (rsa or dsa)'' option.
This option takes a string argument <span class="file">sign</span>.

<p class="noindent">This option has some usage constraints.  It:
     <ul>
<li>must be compiled in by defining <code>AUTOKEY</code> during the compilation.
</ul>

  <p>Generate a new sign key of the designated type, obsoleting any
that may exist.  By default, the program uses the host key as the
sign key.
<div class="node">
<p><hr>
<a name="ntp_002dkeygen-subject_002dname"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-trusted_002dcert">ntp-keygen trusted-cert</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-sign_002dkey">ntp-keygen sign-key</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">subject-name option (-s)</h4>

<p><a name="index-ntp_002dkeygen_002dsubject_002dname-19"></a>
This is the ``set host and optionally group name'' option.
This option takes a string argument <span class="file">host@group</span>.

<p class="noindent">This option has some usage constraints.  It:
     <ul>
<li>must be compiled in by defining <code>AUTOKEY</code> during the compilation.
</ul>

  <p>Set the Autokey host name, and optionally, group name specified
following an '<code>}' character.  The host name is used in the file
name of generated host and signing certificates, without the
group name.  The host name, and if provided, group name are used
in host
  <p>fields.  Specifying '-s
  <p>leaving the host name unchanged while appending
  <p>subject and issuer fields, as with -i group.  The group name, or
if not provided, the host name are also used in the file names
of IFF, GQ, and MV client parameter files.
</code><div class="node">
<p><hr>
<a name="ntp_002dkeygen-trusted_002dcert"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-mv_002dparams">ntp-keygen mv-params</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-subject_002dname">ntp-keygen subject-name</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">trusted-cert option (-T)</h4>

<p><a name="index-ntp_002dkeygen_002dtrusted_002dcert-20"></a>
This is the ``trusted certificate (tc scheme)'' option.

<p class="noindent">This option has some usage constraints.  It:
     <ul>
<li>must be compiled in by defining <code>AUTOKEY</code> during the compilation.
</ul>

  <p>Generate a trusted certificate.  By default, the program generates
a non-trusted certificate.
<div class="node">
<p><hr>
<a name="ntp_002dkeygen-mv_002dparams"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-mv_002dkeys">ntp-keygen mv-keys</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-trusted_002dcert">ntp-keygen trusted-cert</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">mv-params option (-V)</h4>

<p><a name="index-ntp_002dkeygen_002dmv_002dparams-21"></a>
This is the ``generate &lt;num&gt; mv parameters'' option.
This option takes a number argument <span class="file">num</span>.

<p class="noindent">This option has some usage constraints.  It:
     <ul>
<li>must be compiled in by defining <code>AUTOKEY</code> during the compilation.
</ul>

  <p>Generate parameters and keys for the Mu-Varadharajan (MV)
identification scheme.
<div class="node">
<p><hr>
<a name="ntp_002dkeygen-mv_002dkeys"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-config">ntp-keygen config</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-mv_002dparams">ntp-keygen mv-params</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">mv-keys option (-v)</h4>

<p><a name="index-ntp_002dkeygen_002dmv_002dkeys-22"></a>
This is the ``update &lt;num&gt; mv keys'' option.
This option takes a number argument <span class="file">num</span>.

<p class="noindent">This option has some usage constraints.  It:
     <ul>
<li>must be compiled in by defining <code>AUTOKEY</code> during the compilation.
</ul>

  <p>This option has no <span class="samp">doc</span> documentation.

<div class="node">
<p><hr>
<a name="ntp_002dkeygen-config"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-exit-status">ntp-keygen exit status</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-mv_002dkeys">ntp-keygen mv-keys</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">presetting/configuring ntp-keygen</h4>

<p>Any option that is not marked as <i>not presettable</i> may be preset by
loading values from configuration ("rc" or "ini") files, and values from environment variables named <code>NTP-KEYGEN</code> and <code>NTP-KEYGEN_&lt;OPTION_NAME&gt;</code>.  <code>&lt;OPTION_NAME&gt;</code> must be one of
the options listed above in upper case and segmented with underscores.
The <code>NTP-KEYGEN</code> variable will be tokenized and parsed like
the command line.  The remaining variables are tested for existence and their
values are treated like option arguments.

<p class="noindent"><code>libopts</code> will search in 2 places for configuration files:
     <ul>
<li>$HOME
<li>$PWD
</ul>
  The environment variables <code>HOME</code>, and <code>PWD</code>
are expanded and replaced when <span class="file">ntp-keygen</span> runs.
For any of these that are plain files, they are simply processed.
For any that are directories, then a file named <span class="file">.ntprc</span> is searched for
within that directory and processed.

  <p>Configuration files may be in a wide variety of formats.
The basic format is an option name followed by a value (argument) on the
same line.  Values may be separated from the option name with a colon,
equal sign or simply white space.  Values may be continued across multiple
lines by escaping the newline with a backslash.

  <p>Multiple programs may also share the same initialization file.
Common options are collected at the top, followed by program specific
segments.  The segments are separated by lines like:
<pre class="example">    [NTP-KEYGEN]
</pre>
  <p class="noindent">or by
<pre class="example">    &lt;?program ntp-keygen&gt;
</pre>
  <p class="noindent">Do not mix these styles within one configuration file.

  <p>Compound values and carefully constructed string values may also be
specified using XML syntax:
<pre class="example">    &lt;option-name&gt;
       &lt;sub-opt&gt;...&amp;lt;...&amp;gt;...&lt;/sub-opt&gt;
    &lt;/option-name&gt;
</pre>
  <p class="noindent">yielding an <code>option-name.sub-opt</code> string value of
<pre class="example">    "...&lt;...&gt;..."
</pre>
  <p><code>AutoOpts</code> does not track suboptions.  You simply note that it is a
hierarchicly valued option.  <code>AutoOpts</code> does provide a means for searching
the associated name/value pair list (see: optionFindValue).

  <p>The command line options relating to configuration and/or usage help are:

<h5 class="subsubheading">version (-)</h5>

<p>Print the program version to standard out, optionally with licensing
information, then exit 0.  The optional argument specifies how much licensing
detail to provide.  The default is to print just the version.  The licensing infomation may be selected with an option argument.
Only the first letter of the argument is examined:

     <dl>
<dt><span class="samp">version</span><dd>Only print the version.  This is the default.
<br><dt><span class="samp">copyright</span><dd>Name the copyright usage licensing terms.
<br><dt><span class="samp">verbose</span><dd>Print the full copyright usage licensing terms.
</dl>

<div class="node">
<p><hr>
<a name="ntp_002dkeygen-exit-status"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-Usage">ntp-keygen Usage</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-config">ntp-keygen config</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">ntp-keygen exit status</h4>

<p>One of the following exit values will be returned:
     <dl>
<dt><span class="samp">0 (EXIT_SUCCESS)</span><dd>Successful program execution.
<br><dt><span class="samp">1 (EXIT_FAILURE)</span><dd>The operation failed or the command syntax was not valid.
<br><dt><span class="samp">66 (EX_NOINPUT)</span><dd>A specified configuration file could not be loaded.
<br><dt><span class="samp">70 (EX_SOFTWARE)</span><dd>libopts had an internal operational error.  Please report
it to autogen-users@lists.sourceforge.net.  Thank you.
</dl>
  <div class="node">
<p><hr>
<a name="ntp_002dkeygen-Usage"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-Notes">ntp-keygen Notes</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-exit-status">ntp-keygen exit status</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">ntp-keygen Usage</h4>

<div class="node">
<p><hr>
<a name="ntp_002dkeygen-Notes"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#ntp_002dkeygen-Bugs">ntp-keygen Bugs</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-Usage">ntp-keygen Usage</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">ntp-keygen Notes</h4>

<div class="node">
<p><hr>
<a name="ntp_002dkeygen-Bugs"></a>Previous:&nbsp;<a rel="previous" accesskey="p" href="#ntp_002dkeygen-Notes">ntp-keygen Notes</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#ntp_002dkeygen-Invocation">ntp-keygen Invocation</a>
<br>
</div>

<h4 class="subsection">ntp-keygen Bugs</h4>

<div class="node">
<p><hr>
<a name="Random-Seed-File"></a>Next:&nbsp;<a rel="next" accesskey="n" href="#Cryptographic-Data-Files">Cryptographic Data Files</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#Running-the-Program">Running the Program</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#Top">Top</a>
<br>
</div>

<!-- node-name,  next,  previous,  up -->
<h3 class="section">Random Seed File</h3>

<p>All cryptographically sound key generation schemes must have means to
randomize the entropy seed used to initialize the internal
pseudo-random number generator used by the OpenSSL library routines.
If a site supports ssh, it is very likely that means to do this are
already available.
The entropy seed used by the OpenSSL library is contained in a file,
usually called <code>.rnd</code>, which must be available when
starting the <code>ntp-keygen</code> program or <code>ntpd</code> daemon.

  <p>The OpenSSL library looks for the file using the path specified by the
<code>RANDFILE</code> environment variable in the user home directory, whether root
or some other user.
If the <code>RANDFILE</code> environment variable is not
present, the library looks for the <code>.rnd</code> file in the user home
directory.
Since both the <code>ntp-keygen</code> program and <code>ntpd</code> daemon must run
as root, the logical place to put this file is in <code>/.rnd</code> or
<code>/root/.rnd</code>.
If the file is not available or cannot be written, the program exits
with a message to the system log.

<div class="node">
<p><hr>
<a name="Cryptographic-Data-Files"></a>Previous:&nbsp;<a rel="previous" accesskey="p" href="#Random-Seed-File">Random Seed File</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#Top">Top</a>
<br>
</div>

<!-- node-name,  next,  previous,  up -->
<h3 class="section">Cryptographic Data Files</h3>

<p>File and link names are in the <code>form ntpkey_key_name.fstamp</code>,
where <code>key</code> is the key or parameter type,
<code>name</code> is the host or group name and
<code>fstamp</code> is the filestamp (NTP seconds) when the file was created).
By convention, key names in generated file names include both upper and
lower case characters, while key names in generated link names include
only lower case characters. The filestamp is not used in generated link
names.

  <p>The key name is a string defining the cryptographic key type.
Key types include public/private keys host and sign, certificate cert
and several challenge/response key types.
By convention, client files used for
challenges have a par subtype, as in the IFF challenge IFFpar, while
server files for responses have a key subtype, as in the GQ response
GQkey.

  <p>All files begin with two nonencrypted lines. The first line contains
the file name in the format <code>ntpkey_key_host.fstamp</code>.
The second line contains the datestamp in conventional Unix date format.
Lines beginning with <code>#</code> are ignored.

  <p>The remainder of the file contains cryptographic data encoded first
using ASN.1 rules, then encrypted using the DES-CBC algorithm with
given password and finally written in PEM-encoded printable ASCII text
preceded and followed by MIME content identifier lines.

  <p>The format of the symmetric keys file, ordinarily named <code>ntp.keys</code>,
is somewhat different than the other files in the interest of backward
compatibility.
Ordinarily, the file is generated by this program, but
it can be constructed and edited using an ordinary text editor.

<pre class="example">    # ntpkey_MD5key_hms.local.3564038757
    # Sun Dec  9 02:45:57 2012

     1 MD5 "]!ghT%O;3)WJ,/Nc:&gt;I  # MD5 key
     2 MD5 lu+H^tF46BKR-6~pV_5  # MD5 key
     3 MD5 :lnoVsE%Yz*avh%EtNC  # MD5 key
     4 MD5 |fdZrf0sF~^V  # MD5 key
     5 MD5 IyAG&gt;O"y"LmCRS!*bHC  # MD5 key
     6 MD5 "&gt;e\A  # MD5 key
     7 MD5 c9x=M'CfLxax9v)PV-si  # MD5 key
     8 MD5 E|=jvFVov?Bn|Ev=&amp;aK\  # MD5 key
     9 MD5 T!c4UT&amp;`(m$+m+B6,`Q0  # MD5 key
    10 MD5 JVF/1=)=IFbHbJQz..Cd  # MD5 key
    11 SHA1 6dea311109529e436c2b4fccae9bc753c16d1b48  # SHA1 key
    12 SHA1 7076f373d86c4848c59ff8046e49cb7d614ec394  # SHA1 key
    13 SHA1 5f48b1b60591eb01b7cf1d33b7774f08d20262d3  # SHA1 key
    14 SHA1 eed5ab9d9497319ec60cf3781d52607e76720178  # SHA1 key
    15 SHA1 f283562611a04c964da8126296f5f8e58c3f85de  # SHA1 key
    16 SHA1 1930da171297dd63549af50b29449de17dcf341f  # SHA1 key
    17 SHA1 fee892110358cd4382322b889869e750db8e8a8f  # SHA1 key
    18 SHA1 b5520c9fadd7ad3fd8bfa061c8821b65d029bb37  # SHA1 key
    19 SHA1 8c74fb440ec80f453ec6aaa62b9baed0ab723b92  # SHA1 key
    20 SHA1 6bc05f734306a189326000970c19b3910f403795  # SHA1 key
</pre>
  <p>Figure 1. Typical Symmetric Key File

  <p>Figure 1 shows a typical symmetric keys file used by the reference
implementation.
Each line of the file contains three fields, first an
integer between 1 and 65534, inclusive, representing the key identifier
used in the server and peer configuration commands.
Next is the key type for the message digest algorithm,
which in the absence of the
OpenSSL library must be MD5 to designate the MD5 message digest
algorithm.
If the OpenSSL library is installed, the key type can be any
message digest algorithm supported by that library.
However, if
compatibility with FIPS 140-2 is required, the key type must be either
SHA or SHA1.
The key type can be changed using an ASCII text editor.

  <p>An MD5 key consists of a printable ASCII string less than or equal to
16 characters and terminated by whitespace or a # character.
An OpenSSL
key consists of a hex-encoded ASCII string of 40 characters, which is
truncated as necessary.

  <p>Note that the keys used by the <code>ntpq</code> and <code>ntpdc</code> programs are
checked against passwords requested by the programs and entered by hand,
so it
is generally appropriate to specify these keys in human readable ASCII
format.

  <p>The <code>ntp-keygen</code> program generates a MD5 symmetric keys file
<code>ntpkey_MD5key_hostname.filestamp</code>.
Since the file contains private
shared keys, it should be visible only to root and distributed by
secure means to other subnet hosts.
The NTP daemon loads the file <code>ntp.keys</code>, so <code>ntp-keygen</code>
installs a soft link from this name to the generated file.
Subsequently, similar soft links must be installed by
manual or automated means on the other subnet hosts.
While this file is
not used with the Autokey Version 2 protocol, it is needed to
authenticate some remote configuration commands used by the <code>ntpq</code> and
<code>ntpdc</code> utilities.

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