NetBSD/dist/ntp/html/genkeys.htm

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2000-04-22 18:51:59 +04:00
<html><head><title>
<tt>ntp_genkeys</tt> - generate public and private keys
</title></head><body><h3>
<tt>ntp_genkeys</tt> - generate public and private keys
</h3><hr>
<h4>Synopsis</h4>
<tt>ntp_genkeys</tt>
<H4>Description</H4>
<p>The cryptographic values used by the <tt>autokey</tt> scheme are
incorporated as a set of four files generated by the
<tt>ntp_genkeys</tt> program, including <tt>ntp.keys</tt> containing the
DES/MD5 private keys, <tt>ntpkey</tt> containing the RSA private key,
<tt>ntpkey_<i>host</i></tt> containing the RSA public key, where
<tt><i>host</i></tt> is the DNS name of the generating machine, and
<tt>ntpkey_dh</tt> containing the parameters for the Diffie-Hellman key-
agreement algorithm. The files contain cryptographic values generated by
the algorithms of the <tt>rsaref20</tt> package and are in printable
ASCII format. Since the algorythms are seeded by the system clock, each
run of this program will produce a different outcome. There are no
options or frills of any sort, although a number of options would seem
to be appropriate.
<p>The <tt>ntp.keys</tt> file contains 16 MD5 keys. Each key consists of
16 characters randomized over the ASCII 95-character printing subset.
The file is read by the daemon at the location specified by the
<tt>keys</tt> configuration file command and made visible only to root.
An additional key consisting of a easily remembered password should be
added by hand for use with the <tt>ntpq</tt> and <tt>ntpdc</tt>
programs. The file must be distributed by secure means to other servers
and clients sharing the same security compartment. While the key
identifiers for MD5 and DES keys must be in the range 1-65534,
inclusive, the <tt>ntp_genkeys</tt> program uses only the identifiers
from 1 to 16. The key identifier for each association is specified as
the key argument in the <tt>server</tt> or peer configuration file
command.
<p>The <tt>ntpkey</tt> file contains the RSA private key. It is read by
the daemon at the location specified by the <tt>privatekey</tt> argument
of the <tt>crypto</tt> configuration file command and made visible only
to root. This file is useful only to the machine that generated it and
never shared with any other daemon or application program.
<p>The <tt>ntpkey_<i>host</i></tt> file contains the RSA public key,
where <tt><i>host</i></tt> is the DNS name of the host that generated
it. The file is read by the daemon at the location specified by the
<tt>publickey</tt> argument to the <tt>server</tt> or <tt>peer</tt>
configuration file command. This file can be widely distributed and
stored without using secure means, since the data are public values.
<p>The <tt>ntp_dh</tt> file contains two Diffie-Hellman parameters: the
prime modulus and the generator. The file is read by the daemon at the
location specified by the <tt>dhparams</tt> argument of the
<tt>crypto</tt> configuration file command. The file can be distributed
by insecure means to other servers and clients sharing the same key
agreement compartment, since the data are public values.
<p>The file formats begin with two lines, the first containing the
generating system DNS name and the second the datestamp. Lines beginning
with <tt>#</tt> are considered comments and ignored by the daemon. In
the <tt>ntp.keys</tt> file, the next 16 lines contain the MD5 keys in
order. If necessary, this file can be further customized by an ordinary
text editor. The format is described in the following section. In the
<tt>ntpkey</tt> and <tt>ntpkey_<i>host</i></tt> files, the next line
contains the modulus length in bits followed by the key as a PEM encoded
string. In the <tt>ntpkey_dh</tt> file, the next line contains the prime
length in bytes followed by the prime as a PEM encoded string, and the
next and final line contains the generator length in bytes followed by
the generator as a PEM encoded string.
<p>Note: See the file <tt>./source/rsaref.h</tt> in the
<tt>rsaref20</tt> package for explanation of return values, if
necessary.
<H4>Private Key File Format</H4>
In the case of DES, the keys are 56 bits long with, depending on type,
a parity check on each byte. In the case of MD5, the keys are 64 bits (8
bytes). <TT>ntpd</TT> reads its keys from a file specified using the
<TT>-k</TT> command line option or the <TT>keys</TT> 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 of the keys numbered 1
through 15 may be arbitrarily set in the keys file.
<P>The key file uses the same comment conventions as the configuration
file. Key entries use a fixed format of the form
<P><I><TT>keyno type key</TT></I>
<P>where <I><TT>keyno</TT></I> is a positive integer,
<I><TT>type</TT></I> is a single character which defines the key format,
and <I><TT>key</TT></I> is the key itself.
<P>The key may be given in one of three different formats, controlled by
the <I><TT>type</TT></I> character. The three key types, and
corresponding formats, are listed following.
<DL>
<DT><TT>S</TT></DT>
<DD>The key is a 64-bit hexadecimal number in the format specified in
the DES specification; that is, the high order seven bits of each octet
are used to form the 56-bit key while the low order bit of each octet is
given a value such that odd parity is maintained for the octet. Leading
zeroes must be specified (i.e., the key must be exactly 16 hex digits
long) and odd parity must be maintained. Hence a zero key, in standard
format, would be given as <TT>0101010101010101</TT>.</DD>
<DT><TT>N</TT></DT>
<DD>The key is a 64-bit hexadecimal number in the format specified in
the NTP standard. This is the same as the DES format, except the bits in
each octet have been rotated one bit right so that the parity bit is now
the high order bit of the octet. Leading zeroes must be specified and
odd parity must be maintained. A zero key in NTP format would be
specified as <TT>8080808080808080</TT>.</DD>
<DT><TT>A</TT></DT>
<DD>The key is a 1-to-8 character ASCII string. A key is formed from
this by using the low order 7 bits of each ASCII character in the
string, with zeroes added on the right when necessary to form a full
width 56-bit key, in the same way that encryption keys are formed from
Unix passwords.</DD>
<DT><TT>M</TT></DT>
<DD>The key is a 1-to-8 character ASCII string, using the MD5
authentication scheme. Note that both the keys and the authentication
schemes (DES or MD5) must be identical between a set of peers sharing
the same key number.</DD>
</DL>
<p>Note that the keys used by the <TT>ntpq</TT> and <TT>ntpdc</TT>
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.
<h4>Files</h4>
The RSA Laboratories package <tt>rsaref20</tt> of cryptographic routines
is necessary in order to build and use this program.
<h4>Bugs</h4>
It can take quite a while to generate the RSA public/private key pair
and Diffie-Hellman parameters, from a few seconds on a modern
workstation to several minutes on older machines.
2000-04-22 20:46:49 +04:00
<hr><a href=index.htm>Home</a><address><a
2000-04-22 18:51:59 +04:00
href=mailto:mills@udel.edu> David L. Mills &lt;mills@udel.edu&gt;</a>
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