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ntp-keygen(8)							 ntp-keygen(8)

NAME
       ntp-keygen - generate public and private keys

SYNOPSIS
       ntp-keygen  [ -deGgHIMPT ] [ -c [RSA-MD2 | RSA-MD5 | RSA-SHA | RSA-SHA1
       | RSA-MDC2 | RSA-RIPEMD160 | DSA-SHA | DSA-SHA1 ] ] [ -C cipher ] [  -i
       name  ] [ -m modulus ] [ -p password ] [ -q password ] [ -S [ RSA | DSA
       ] ] [ -s name ] [ -v nkeys ] [ -V nkeys ]

DESCRIPTION
       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	 soft‐
       ware  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 identi‐
       fication algorithms compatible with the Internet standard security  in‐
       frastructure.

       By  default,  files  are	 not  encrypted by ntp-keygen. The -p password
       option specifies the write password and -q  password  option  the  read
       password for previously encrypted files. The ntp-keygen program prompts
       for the password if it reads an encrypted  file	and  the  password  is
       missing	or incorrect. If an encrypted file is read successfully and no
       write password is specified, the read password is  used	as  the	 write
       password by default.

       The  ntpd  configuration	 command crypto pw password 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.

       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.  File names begin with the prefix ntpkey_ and end with the
       postfix _hostname.filestamp,  where  hostname  is  usually  the	string
       returned	 by  the  Unix gethostname() routine, and filestamp is the NTP
       seconds when the file was generated, in decimal digits. This both guar‐
       antees  uniqueness  and	simplifies  maintenance	 procedures, since all
       files can be quickly removed by a rm ntpkey* command or all files  gen‐
       erated at a specific time can be removed by a rm *filestamp 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.

       All  files are installed by default in the keys directory /etc/ntp. 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.

       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.

       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, ntpd extracts the filestamp from
       the file itself. This allows clients to verify that the file and gener‐
       ation  times  are  always current. The ntp-keygen program uses the same
       extension for all files generated at one time, so  each	generation  is
       distinct and can be readily recognized in monitoring data.

RUNNING THE PROGRAM
       The  safest  way to run the ntp-keygen program is logged in directly as
       root. The recommended procedure is change to the keys  directory,  usu‐
       ally /etc/ntp, then run the program. When run for the first time, or if
       all ntpkey 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.

       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	 algo‐
       rithms.	However,  the scheme specified in the certificate must be com‐
       patible 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.

       Private/public key files and certificates  are  compatible  with	 other
       OpenSSL	applications and very likely other libraries as well. Certifi‐
       cates 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.

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

       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  /etc	 using	the  keysdir  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.

       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.

TRUSTED HOSTS AND GROUPS
       Each  cryptographic  configuration  involves  selection	of a signature
       scheme and identification scheme, called a cryptotype, as explained  in
       the  Authentication  Options  page.  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 cer‐
       tificates. These hosts will automatically and dynamically build author‐
       itative	certificate  trails  to	 one  or more trusted hosts. A trusted
       group is the set of all hosts that have, directly or indirectly, a cer‐
       tificate trail ending at a trusted host. The trail is defined by static
       configuration file entries or dynamic means described on the  Automatic
       NTP Configuration Options page.

       On each trusted host as root, change to the keys directory. To insure a
       fresh fileset, remove all ntpkey files. Then run ntp-keygen -T to  gen‐
       erate  keys  and a trusted certificate. On all other hosts do the same,
       but leave off the -T 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 instanti‐
       ate  the	 certificate  trails throughout the subnet, but setting up the
       environment is completely automatic.

       If it is necessary to use a different sign key or different digest/sig‐
       nature scheme than the default, run ntp-keygen with the -S type option,
       where type is either RSA or DSA. 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 ntp-keygen with the -c	scheme
       option  and selected scheme as needed. If ntp-keygen is run again with‐
       out these options, it generates a new certificate using the same scheme
       and sign key.

       After setting up the environment it is advisable to update certificates
       from time to time, if only to extend the validity interval. Simply  run
       ntp-keygen  with	 the same flags as before to generate new certificates
       using existing keys. However, if the host or sign key is changed,  ntpd
       should be restarted. When ntpd 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.

IDENTITY SCHEMES
       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. 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.

       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  non‐
       trusted	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.

       The  PC	scheme supports only one trusted host in the group. On trusted
       host alice run ntp-keygen -P -p password to generate the host key  file
       ntpkey_RSAkey_alice.filestamp and trusted private certificate file ntp‐
       key_RSA-MD5_cert_alice.filestamp. 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 ntpkey_host_bob
       to  the host key file and soft link ntpkey_cert_bob to the private cer‐
       tificate 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.

       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 ntp-
       keygen -T -I -p password to  produce  her  parameter  file  ntpkey_IFF‐
       par_alice.filestamp,  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 ntpkey_iff_alice 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.

       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 ntp-keygen -e 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 ntpkey_iff_alice  to  this
       file.  To  further  protect the integrity of the keys, each file can be
       encrypted with a secret password.

       For the GQ scheme proceed as in the TC scheme to generate keys and cer‐
       tificates  for  all  group  hosts,  then	 for every trusted host in the
       group, generate the IFF parameter file. On trusted host alice run  ntp-
       keygen	-T   -G	 -p  password  to  produce  her	 parameter  file  ntp‐
       key_GQpar_alice.filestamp, which includes both server and client	 keys.
       Copy  this  file	 to  all  group hosts and install a soft link from the
       generic ntpkey_gq_alice to this file. In addition,  on  each  host  bob
       install	a soft link from generic ntpkey_gq_bob 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.

       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 ntp-keygen -V n -p password, where	n  is  the  number  of
       revokable  keys	(typically  5)	to  produce  the  parameter  file ntp‐
       keys_MVpar_trish.filestamp    and     client	key	files	  ntp‐
       keys_MVkeyd_trish.filestamp where d is the key number (0 < d < n). Copy
       the parameter file to alice and install a soft link  from  the  generic
       ntpkey_mv_alice 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 clients. On client bob install a soft
       link  from  generic  ntpkey_mvkey_bob to the client key file. As the MV
       scheme is independent of keys and  certificates,	 these	files  can  be
       refreshed as needed.

COMMAND LINE OPTIONS
       -c  [ RSA-MD2 | RSA-MD5 | RSA-SHA | RSA-SHA1 | RSA-MDC2 | RSA-RIPEMD160
       | DSA-SHA | DSA-SHA1 ]
	       Select 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.

       -C cipher
	       Select the cipher which is used to encrypt the files containing
	       private keys. The default is DES in CBC mode, equivalent to "-C
	       des-cbc".  The openssl tool lists ciphers available in "openssl
	       -h" output.

       -d      Enable debugging. This option displays the  cryptographic  data
	       produced in eye-friendly billboards.

       -e      Write  the  IFF	client	keys  to  the standard output. This is
	       intended for automatic key distribution by mail.

       -G      Generate parameters and keys for the GQ identification  scheme,
	       obsoleting any that may exist.

       -g      Generate keys for the GQ identification scheme using the exist‐
	       ing GQ parameters. If the GQ parameters do not yet exist,  cre‐
	       ate them first.

       -H      Generate new host keys, obsoleting any that may exist.

       -I      Generate parameters for the IFF identification scheme, obsolet‐
	       ing any that may exist.

       -i name Set the subject name to name. This is used as the subject field
	       in certificates and in the file name for host and sign keys.

       -M      Generate MD5 keys, obsoleting any that may exist.

       -m modulus
	       Set  prime  modulus  size in bits (256 - 2048). Default size is
	       512.

       -P      Generate a private certificate. By default, the program	gener‐
	       ates public certificates.

       -p password
	       Encrypt	generated  files containing private data with password
	       and the DES-CBC algorithm.

       -q password
	       Set the password for reading files to password.

       -S [ RSA | DSA ]
	       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.

       -s name Set the issuer name to name. This is used for the issuer	 field
	       in certificates and in the file name for identity files.

       -T      Generate	 a trusted certificate. By default, the program gener‐
	       ates a non-trusted certificate.

       -V nkeys
	       Generate parameters and keys for the Mu-Varadharajan (MV) iden‐
	       tification scheme.

RANDOM SEED FILE
       All  cryptographically  sound key generation schemes must have means to
       randomize the entropy seed used to initialize the internal  pseudo-ran‐
       dom  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 ntp-keygen program. If a
       site supports OpenSSL or its companion OpenSSH, it is very likely  that
       means to do this are already available.

       It  is  important  to  understand that entropy must be evolved for each
       generation, for otherwise the random  number  sequence  would  be  pre‐
       dictable. 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.

       The entropy seed used by the OpenSSL library is contained  in  a	 file,
       usually called .rnd, which must be available when starting the NTP dae‐
       mon or the ntp-keygen program. The NTP daemon will first look  for  the
       file  using the path specified by the randfile subcommand of the crypto
       configuration command. If not specified in this way, or	when  starting
       the  ntp-keygen	program,  the  OpenSSL	library will look for the file
       using the path specified by the RANDFILE environment  variable  in  the
       user  home  directory, whether root or some other user. If the RANDFILE
       environment variable is not present, the library will look for the .rnd
       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.

CRYPTOGRAPHIC DATA FILES
       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 begin‐
       ning with # are considered comments and ignored by the ntp-keygen  pro‐
       gram  and  ntpd	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.

       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  alphanu‐
       meric  strings.	Following the header the keys are entered one per line
       in the format

       keyno type key

       where keyno is a positive integer in the range 1-65,535,	 type  is  the
       string  MD5 defining the key format and key is the key itself, which is
       a printable ASCII string 16 characters or less in length. Each  charac‐
       ter  is	chosen	from  the  93  printable  characters in the range 0x21
       through 0x7f excluding space and the '#' character.

       Note that the keys used by the ntpq  and	 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  ntp-keygen	program	 generates  a  MD5  symmetric  keys  file ntp‐
       key_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 ntp.keys, so  ntp-
       keygen  installs a soft link from this name to the generated file. Sub‐
       sequently, 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 ntpq and ntpdc utilities.

BUGS
       It  can	take quite a while to generate some cryptographic values, from
       one to several minutes with modern architectures such as UltraSPARC and
       up to tens of minutes to an hour with older architectures such as SPARC
       IPC.

SEE ALSO
       ntpd(8), ntp_auth(5)

       Primary source of documentation: /usr/share/doc/ntp-*

       This file was automatically generated from HTML source.

								 ntp-keygen(8)
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