182 lines
7.6 KiB
HTML
182 lines
7.6 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
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<html>
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<head>
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<meta name="generator" content="HTML Tidy, see www.w3.org">
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<title>ntp-genkeys - generate public and private keys</title>
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</head>
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<body>
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<h3><tt>ntp-genkeys</tt> - generate public and private keys</h3>
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<img align="left" src="pic/alice23.gif" alt="gif"><a href=
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"http://www.eecis.udel.edu/~mills/pictures.htm">from <i>Alice's
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Adventures in Wonderland</i>, Lewis Carroll</a>
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<p>Alice holds the key.<br clear="left">
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</p>
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<hr>
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<h4>Synopsis</h4>
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<tt>ntp-genkeys</tt>
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<h4>Description</h4>
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<p>This program generates random keys used by either or both the
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NTPv3/NTPv4 symmetric key or the NTPv4 public key (Autokey)
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cryptographic authentication schemes. By default the program
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generates the <tt>ntp.keys</tt> file containing 16 random symmetric
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keys. In addition, if the <tt>rsaref20</tt> package is configured
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for the software build, the program generates cryptographic values
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used by the Autokey scheme. These values are incorporated as a set
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of three files, <tt>ntpkey</tt> containing the RSA private key,
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<tt>ntpkey_<i>host</i></tt> containing the RSA public key, where
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<tt><i>host</i></tt> is the DNS name of the generating machine, and
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<tt>ntpkey_dh</tt> containing the parameters for the Diffie-Hellman
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key-agreement algorithm. All files and are in printable ASCII
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format. A timestamp in NTP seconds is appended to each. Since the
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algorithms are seeded by the system clock, each run of this program
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produces a different file and file name.</p>
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<p>The <tt>ntp.keys</tt> file contains 16 MD5 keys. Each key
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consists of 16 characters randomized over the ASCII 95-character
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printing subset. The file is read by the daemon at the location
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specified by the <tt>keys</tt> configuration file command and made
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visible only to root. An additional key consisting of a easily
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remembered password should be added by hand for use with the <tt>
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ntpq</tt> and <tt>ntpdc</tt> programs. The file must be distributed
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by secure means to other servers and clients sharing the same
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security compartment. While the key identifiers for MD5 and DES
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keys must be in the range 1-65534, inclusive, the <tt>
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ntp-genkeys</tt> program uses only the identifiers from 1 to 16.
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The key identifier for each association is specified as the key
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argument in the <tt>server</tt> or peer configuration file
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command.</p>
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<p>The <tt>ntpkey</tt> file contains the RSA private key. It is
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read by the daemon at the location specified by the <tt>
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privatekey</tt> argument of the <tt>crypto</tt> configuration file
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command and made visible only to root. This file is useful only to
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the machine that generated it and never shared with any other
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daemon or application program.</p>
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<p>The <tt>ntpkey_<i>host</i></tt> file contains the RSA public
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key, where <tt><i>host</i></tt> is the DNS name of the host that
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generated it. The file is read by the daemon at the location
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specified by the <tt>publickey</tt> argument to the <tt>server</tt>
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or <tt>peer</tt> configuration file command. This file can be
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widely distributed and stored without using secure means, since the
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data are public values.</p>
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<p>The <tt>ntp_dh</tt> file contains two Diffie-Hellman parameters:
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the prime modulus and the generator. The file is read by the daemon
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at the location specified by the <tt>dhparams</tt> argument of the
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<tt>crypto</tt> configuration file command. The file can be
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distributed by insecure means to other servers and clients sharing
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the same key agreement compartment, since the data are public
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values.</p>
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<p>The file formats begin with two lines, the first containing the
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generating system DNS name and the second the datestamp. Lines
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beginning with <tt>#</tt> are considered comments and ignored by
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the daemon. In the <tt>ntp.keys</tt> file, the next 16 lines
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contain the MD5 keys in order. If necessary, this file can be
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further customized by an ordinary text editor. The format is
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described in the following section. In the <tt>ntpkey</tt> and <tt>
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ntpkey_<i>host</i></tt> files, the next line contains the modulus
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length in bits followed by the key as a PEM encoded string. In the
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<tt>ntpkey_dh</tt> file, the next line contains the prime length in
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bytes followed by the prime as a PEM encoded string, and the next
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and final line contains the generator length in bytes followed by
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the generator as a PEM encoded string.</p>
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<p>Note: See the file <tt>./source/rsaref.h</tt> in the <tt>
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rsaref20</tt> package for explanation of return values, if
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necessary.</p>
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<h4>Symmetric Key File Format</h4>
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In the case of DES, the keys are 56 bits long with, depending on
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type, a parity check on each byte. In the case of MD5, the keys are
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64 bits (8 bytes). <tt>ntpd</tt> reads its keys from a file
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specified using the <tt>-k</tt> command line option or the <tt>
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keys</tt> statement in the configuration file. While key number 0
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is fixed by the NTP standard (as 56 zero bits) and may not be
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changed, one or more of the keys numbered 1 through 15 may be
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arbitrarily set in the keys file.
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<p>The key file uses the same comment conventions as the
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configuration file. Key entries use a fixed format of the form</p>
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<p><i><tt>keyno type key</tt></i></p>
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<p>where <i><tt>keyno</tt></i> is a positive integer, <i><tt>
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type</tt></i> is a single character which defines the key format,
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and <i><tt>key</tt></i> is the key itself.</p>
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<p>The key may be given in one of three different formats,
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controlled by the <i><tt>type</tt></i> character. The three key
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types, and corresponding formats, are listed following.</p>
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<dl>
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<dt><tt>S</tt></dt>
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<dd>The key is a 64-bit hexadecimal number in the format specified
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in the DES specification; that is, the high order seven bits of
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each octet are used to form the 56-bit key while the low order bit
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of each octet is given a value such that odd parity is maintained
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for the octet. Leading zeroes must be specified (i.e., the key must
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be exactly 16 hex digits long) and odd parity must be maintained.
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Hence a zero key, in standard format, would be given as <tt>
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0101010101010101</tt>.</dd>
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<dt><tt>N</tt></dt>
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<dd>The key is a 64-bit hexadecimal number in the format specified
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in the NTP standard. This is the same as the DES format, except the
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bits in each octet have been rotated one bit right so that the
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parity bit is now the high order bit of the octet. Leading zeroes
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must be specified and odd parity must be maintained. A zero key in
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NTP format would be specified as <tt>8080808080808080</tt>.</dd>
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<dt><tt>A</tt></dt>
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<dd>The key is a 1-to-8 character ASCII string. A key is formed
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from this by using the low order 7 bits of each ASCII character in
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the string, with zeroes added on the right when necessary to form a
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full width 56-bit key, in the same way that encryption keys are
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formed from Unix passwords.</dd>
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<dt><tt>M</tt></dt>
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<dd>The key is a 1-to-8 character ASCII string, using the MD5
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authentication scheme. Note that both the keys and the
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authentication schemes (DES or MD5) must be identical between a set
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of peers sharing the same key number.</dd>
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</dl>
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<p>Note that the keys used by the <tt>ntpq</tt> and <tt>ntpdc</tt>
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programs are checked against passwords requested by the programs
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and entered by hand, so it is generally appropriate to specify
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these keys in ASCII format.</p>
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<h4>Files</h4>
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The RSA Laboratories package <tt>rsaref20</tt> of cryptographic
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routines is necessary in order to build and use this program.
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<h4>Bugs</h4>
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It can take quite a while to generate the RSA public/private key
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pair and Diffie-Hellman parameters, from a few seconds on a modern
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workstation to several minutes on older machines.
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<hr>
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<a href="index.htm"><img align="left" src="pic/home.gif" alt=
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"gif"></a>
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<address><a href="mailto:mills@udel.edu">David L. Mills
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<mills@udel.edu></a></address>
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</body>
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</html>
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