ntp/util/ntp-keygen.texi

\input texinfo    @c -*-texinfo-*-
@c %**start of header
@setfilename ntp-keygen.info
@settitle Ntp-keygen User's Manual
@include ../sntp/include/version.texi
@paragraphindent 2
@c %**end of header

@ifinfo
This file documents the use of the NTP Project's @code{ntp-keygen}
program, which generates various keys for @code{ntpd},
@end ifinfo

@direntry
* ntp-keygen: (ntp-keygen).                   NTP Key Generation
@end direntry

@titlepage
@title NTP Key Generation User's Manual
@subtitle ntp-keygen, version @value{VERSION}, @value{UPDATED}
@c @author Max @email{foo@ntp.org}
@end titlepage

@c @page
@c @vskip 0pt plus 1filll

@shortcontents

@menu
* Description::
* ntp-keygen Invocation::	Invoking ntp-keygen
* Running the Program::
* Random Seed File::
* Cryptographic Data Files::
@end menu

@node Top, Description, (dir), (dir)
@top NTP Key Generation Program User Manual

This document describes the use of the NTP Project's @code{ntp-keygen}
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.

This document applies to version @value{VERSION} of @code{ntp-keygen}.

@node Description, Running the Program, Top, Top
@comment  node-name,  next,  previous,  up
@section Description

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.

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.

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.

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

The @kbd{pw} option of the @code{crypto} 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.

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}, is
usually installed in @code{/etc}.
Other files and links are usually installed
in @code{/usr/local/etc}, 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}.

This program directs commentary and error messages to the standard
error stream @code{stderr} and remote files to the standard output stream
@code{stdout} 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} and include the file type,
generating host and filestamp,
as described in the @ref{Cryptographic Data Files} section below.

@node Running the Program, Random Seed File, Description, Top
@comment  node-name,  next,  previous,  up
@section Running the Program

To test and gain experience with Autokey concepts, log in as root and
change to the keys directory, usually @code{/usr/local/etc}.
When run for the
first time, or if all files with names beginning @code{ntpkey}] have been
removed, use the @code{ntp-keygen} 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.

Run the command on as many hosts as necessary.
Designate one of them as the trusted host (TH) using @code{ntp-keygen}
with the @code{-T} 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.

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} 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} 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.

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

@include invoke-ntp-keygen.texi

@node Random Seed File, Cryptographic Data Files, Running the Program, Top
@comment  node-name,  next,  previous,  up
@section Random Seed File

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}, which must be available when
starting the @code{ntp-keygen} program or @code{ntpd} daemon.

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

@node Cryptographic Data Files,  , Random Seed File, Top
@comment  node-name,  next,  previous,  up
@section Cryptographic Data Files

File and link names are in the @code{form ntpkey_key_name.fstamp},
where @code{key} is the key or parameter type,
@code{name} is the host or group name and
@code{fstamp} 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.

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.

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

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.

The format of the symmetric keys file, ordinarily named @code{ntp.keys},
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.

@example
# ntpkey_MD5key_hms.local.3564038757
# Sun Dec  9 02:45:57 2012

 1 MD5 "]!ghT%O;3)WJ,/Nc:>I  # MD5 key
 2 MD5 lu+H^tF46BKR-6~p{V_5  # MD5 key
 3 MD5 :lnoVsE%Y}z*avh%EtNC  # MD5 key
 4 MD5 |fdZrf0sF~@PHZ;w-i^V  # MD5 key
 5 MD5 IyAG>O"}y"LmCRS!*bHC  # MD5 key
 6 MD5 ">e\A@>hT/661ri52,,H  # MD5 key
 7 MD5 c9x=M'CfLxax9v)PV-si  # MD5 key
 8 MD5 E|=jvFVov?Bn|Ev=&aK\  # MD5 key
 9 MD5 T!c4UT&`(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
@end example

                  Figure 1. Typical Symmetric Key File

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.

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.

Note that the keys used by the @code{ntpq} and @code{ntpdc} 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.

The @code{ntp-keygen} program generates a MD5 symmetric keys file
@code{ntpkey_MD5key_hostname.filestamp}.
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}, so @code{ntp-keygen}
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} and
@code{ntpdc} utilities.