Manual Pages for UNIX Darwin command on man ntp-keygen

NTPKEYGEN(8) BSD System Manager's Manual NTPKEYGEN(8)

NAME

nnttpp-kkeeyyggeenn - generate public and private keys

SYNOPSIS

nnttpp-kkeeyyggeenn [-ddeeGGggHHIIMMnnPPTT]

[-ii name] [-pp password] [-SS -{{RRSSAA | -DDSSAA}}] [-ss name] [-vv keys]

DESCRIPTION

This program generates cryptographic data files used by the NTPv4 authen-

tication 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 encryp-

tion, digital signature and challenge/response identification algorithms compatible with the Internet standard security infrastructure.

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. 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 pass-

word if it reads an encrypted file and the password is missing or incor-

rect. 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.

File names begin with the prefix ntpkey and end with the postfix host-

name.filestamp, where hostname is the owner name, usually the string

returned by the Unix gethostname() routine, and filestamp is the NTP sec-

onds 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 rm ntpkey* command or all files generated at a spe-

cific 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 /usr/local/etc,

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. 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 spec-

ified 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 generation times are

always current. The ntp-keygen 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. RRuunnnniinngg tthhee pprrooggrraamm

The safest way to run the ntp-keygen program is logged in directly as

root. The recommended procedure is change to the keys directory, usually /ust/local/etc, 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 neces-

sary 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 sup-

ported 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. 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 interpreta-

tion of X509v3 extension fields somewhat liberal. However, the identifi-

cation 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. However, 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 proto-

col. 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 gener-

ating the files, but can be changed by command line options. It is conve-

nient 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. TTrruusstteedd HHoossttss aanndd GGrroouuppss 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 certificates.

These hosts will automatically and dynamically build authoritative cer-

tificate trails to one or more trusted hosts. A trusted group is the set

of all hosts that have, directly or indirectly, a certificate trail end-

ing 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 gener-

ate 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 work-

ing 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.

If it is necessary to use a different sign key or different digest/signa-

ture 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 without

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. IIddeennttiittyy SScchheemmeess

As mentioned on the Autonomous Authentication page, the default TC iden-

tity 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 cer-

tificate. 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 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. 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

ntpkeyRSAkeyalice.filestamp and trusted private certificate file ntp-

keyRSA-MD5certalice.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 ntpkeyhostbob to the host key file and soft link ntpkeycertbob 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.

For the IFF 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

-I -p password to produce her parameter file ntpkeyIFF-

paralice.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 ntpkeyiffalice to this file. If

there are no hosts restricted to operate only as clients, there is noth-

ing further to do. As the IFF scheme is independent of keys and certifi-

cates, these files can be refreshed as needed.

If a rogue client has the parameter file, it could masquerade as a legit-

imate 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 ntpkeyiffalice to this file. To further protect

the integrity of the keys, each file can be encrypted with a secret pass-

word.

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-

keyGQparalice.filestamp, which includes both server and client keys. Copy this file to all group hosts and install a soft link from the generic ntpkeygqalice to this file. In addition, on each host bob install a soft link from generic ntpkeygqbob 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 cer-

tificates 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-

keysMVpartrish.filestamp and client key files ntp-

keysMVkeydtrish.filestamp where d is the key number (0 < d < n). Copy

the parameter file to alice and install a soft link from the generic ntp-

keymvalice 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 ntpkeymvkeybob to the client key file. As the MV scheme is independent of keys and certificates, these files can be refreshed as needed. OOPPTTIIOONNSS

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.

-dd Enable debugging. This option displays the cryptographic data

produced in eye-friendly billboards.

-ee Write the IFF client keys to the standard output. This is

intended for automatic key distribution by mail.

-GG Generate parameters and keys for the GQ identification scheme,

obsoleting any that may exist.

-gg Generate keys for the GQ identification scheme using the existing

GQ parameters. If the GQ parameters do not yet exist, create them first.

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

-II Generate parameters for the IFF identification scheme, obsoleting

any that may exist.

-ii name

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

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

-PP Generate a private certificate. By default, the program generates

public certificates.

-pp password

Encrypt generated files containing private data with password and

the DES-CBC algorithm.

-qq Set the password for reading files to password.

-SS 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.

-ss name

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

-TT Generate a trusted certificate. By default, the program generates

a non-trusted certificate.

-vv nkeys

Generate parameters and keys for the Mu-Varadharajan (MV) identi-

fication scheme. RRaannddoomm SSeeeedd FFiillee 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 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 gen-

eration, 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.

The entropy seed used by the OpenSSL library is contained in a file, usu-

ally called .rnd, which must be available when starting the NTP daemon 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 speci-

fied 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 suit-

able error message. CCrryyppttooggrraapphhiicc DDaattaa FFiilleess All other file formats begin with two lines. The first contains the file

name, including the generated host name and filestamp. The second con-

tains the datestamp in conventional Unix date format. Lines beginning

with # are considered comments and ignored by the ntp-keygen program 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 alphanumeric

strings. Following the herd the keys are entered one per line in the for-

mat 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 character 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 for-

mat.

The ntp-keygen program generates a MD5 symmetric keys file ntp-

keyMD5keyhostname.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. Subse-

quently, 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 con-

figuration commands used by the ntpq and ntpdc utilities.

BUGS

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. BSD October 13, 2003 BSD