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ssh-server-config — SSH Tectia Server configuration file format
The SSH Tectia Server configuration file ssh-server-config.xml
is a valid XML file.
On Unix, the configuration related files are stored in the following directories:
/etc/ssh2/ contains the ssh-server-config.xml file
/etc/ssh2/ssh-tectia/auxdata/ssh-server-ng contains the XML DTD.
On Windows, the configuration related files are stored in the following directories:
"C:\Program Files\SSH Communications Security\SSH Tectia\SSH Tectia Server" contains the ssh-server-config.xml file
"C:\Program Files\SSH Communications Security\SSH Tectia\SSH Tectia AUX\ssh-server-ng" contains the XML DTD.
If the configuration file cannot be found or some of the elements are
missing, hardcoded default values are used. You can view the default values
in the ssh-server-config-default.xml file that is stored in
the same directory with the configuration file.
The ssh-server-config.xml configuration file is
divided in four blocks:
general server parameters (params)
connection rules and encryption methods (connections)
authentication rules and methods (authentication-methods)
service rules (services)
In the connections and authentication-methods
blocks, different selectors can be used to set
access rules to users based on the user parameters such as user name or
location. Users can be divided to groups dynamically, for example, based
on the authentication method they use to log in. In the
services block, each group can then be allowed or denied
services such as tunneling, file transfer, and terminal access.
The server configuration file is a valid XML file and starts with the
Document Type Declaration (DTD) inside the DOCTYPE element.
Both the DOCTYPE declaration and the DTD are mandatory;
should they be missing, the server will not be able to parse the
configuration properly.
The root element in the configuration file is secsh-server.
It can include params, connections,
authentication-methods, and services elements.
These elements in turn can include more elements according to the configuration
file syntax, see Appendix A.
An example of an empty configuration file is shown below:
<!DOCTYPE secsh-server SYSTEM
"../auxdata/ssh-server-ng/ssh-server-ng-config-1.dtd">
<secsh-server>
<params />
<connections>
<connection />
</connections>
<authentication-methods />
<services>
<rule />
</services>
</secsh-server>![[Note]](images/note.gif) | Note |
|---|---|
It is not mandatory to include all elements in the configuration file.
If an element is missing, the equivalent default values shown in the
|
params BlockThe params block defines the general server
parameters, such as the location of the host key file, the listen
address, logging, connection limits, and certificate validation
settings.
This element selects the cryptographic library mode to be used.
Either the standard version (standard) or the FIPS 140-2
certified version (fips) of the crypto library can be
used. The library name is given as a value of the mode
attribute. By default, standard crypto libraries are used.
<crypto-lib mode="standard" />
In the FIPS mode, the cryptographic operations are performed
according to the rules of the FIPS 140-2 standard. The FIPS library
includes the
3des-cbc,
aes128-cbc,
aes192-cbc,
and
aes256-cbc ciphers and the
hmac-sha1 MAC.
| Note |
|---|---|
Setting the FIPS mode does not prevent using algorithms from crypto plugins. For example, CryptiCore can be used even when the main crypto library is set in the FIPS mode. To enforce that only FIPS-compliant algorithms are used, disable the non-FIPS algorithms from the configuration. See also cipher and mac. |
For a list of platforms on which the FIPS library has been validated or tested, see SSH Tectia Client/Server Product Description.
This element contains miscellaneous settings. It has the following
attributes: proxy-scheme, xauth-path,
x11-listen-address, pam-account-checking-only,
resolve-client-hostname,
ignore-aix-rlogin, ignore-aix-login,
record-ptyless-sessions, user-config-dir,
default-path, windows-logon-type,
windows-terminal-mode, ignore-nisplus-no-permission, and
quiet-login.
The proxy-scheme attribute
defines rules for HTTP or SOCKS proxy servers that SSH Tectia Server uses when a
client forwards a connection (local tunnel).
The format of the attribute value is a sequence of rules
delimited by semicolons (;). Each rule has a format
that resembles the URL format. In a rule, the connection type is
given first. The type can be direct,
socks, socks4, socks5, or
http-connect (socks is a synonym for
socks4). This is followed by the server address and
port. If the port is not given, the default ports 1080 for SOCKS and
80 for HTTP are used.
After the address, zero or more conditions delimited by commas (,) are given. The conditions can specify IP addresses or DNS names.
direct:///[cond[,cond]...] socks://server/[cond[,cond]...] socks4://server/[cond[,cond]...] socks5://server/[cond[,cond]...] http-connect://server/[cond[,cond]...]
The IP address/port conditions have an address pattern and an optional port range:
ip_pattern[:port_range]
The ip_pattern may have one of the following forms:
a single IP address x.x.x.x
an IP address range of the form x.x.x.x-y.y.y.y
an IP sub-network mask of the form x.x.x.x/y
The DNS name conditions consist of a hostname which may be a regular expression containing the characters "*" and "?" and a port range:
name_pattern[:port_range]
An example proxy-scheme is shown below. It causes
the server to access the callback address and the ssh.com
domain directly, access *.example with HTTP CONNECT, and
all other destinations with SOCKS4.
"direct:///127.0.0.0/8,*.ssh.com; http-connect://http-proxy.ssh.com:8080/*.example; socks://fw.ssh.com:1080/"
The xauth-path attribute
contains a path to a supplementary XAuth binary used with X11
forwarding on Unix platforms.
On Unix, the x11-listen-address attribute can be
used to configure on what kind of address the x11 listener (used in X11
forwarding) is created. Possible values are:
localhost (default) - sets the DISPLAY
environment variable to 127.0.0.1:<screen>, where
<screen> is the tunneled screen number, typically
10.0. This means that the x11 listener is bound to a loopback address;
this setting should be sufficient for most use cases.
any - sets the DISPLAY environment variable to
<address:screen>, where <address>
is the interface to which the SSH session is bound (typically the first
network interface) and the <screen> is the tunneled
screen number, typically 10.0. This setting will bind the X11 listener to
the 0.0.0.0 (wildcard) interface thereby allowing connections to the proxy
from other hosts. Use this setting on HPUX systems, if you need to tunnel
older X11 applications (such as hpterm).
When x11-listen-address=any, the SO_REUSEADDR
socket option will be left non-set in order to prevent the possibility of
session hijacking on some operating systems by other users binding to the
same port with a more specific address.
On Unix, the pam-account-checking-only attribute
can be used to define that only PAM will be used to check if the user is
allowed to login (for example, the account is not locked). Generally, PAM
can be used during authentication or in PAM account or session management
via the pam-calls-with-commands setting.
Possible values for the pam-account-checking-only
attribute are:
yes - only PAM is used to check the user account
and SSH Tectia Server will not try to independently verify whether the account
has been locked or otherwise disabled, if either PAM authentication has
succeeded or if pam-calls-with-commands is set.
no (default) - the normal system checks will be used
to determine whether the user is allowed to login, regardless of the result
of PAM authentication or the pam-calls-with-commands setting.
The resolve-client-hostname attribute can be used
to define whether SSH Tectia Server should try to resolve the client host name
from the client IP address during connection setup.
| Note |
|---|---|
This attribute does not affect the resolution of TCP tunnel endpoints and SSH Tectia Server will try to resolve the client host name when creating a TCP tunnel. |
Possible values for the resolve-client-hostname
attribute are:
yes (default) - DNS lookups are used to resolve the
client host name at connection time
no - client host name resolution is not attempted,
but the IP address is used as the returned client host name. This is useful
when you know that the DNS cannot be reached, and the query would cause just
additional delay in logging in.
The ignore-aix-rlogin attribute defines whether the
server should ignore the remote login restriction on AIX.
Possible values are:
yes - SSH Tectia Server will ignore these operating
system settings:
the rlogin restriction flag
the unable to login at this time flags (e.g. logintimes)
no (default)
The ignore-aix-login attribute defines whether the
server should ignore the local login restriction on AIX.
Possible values are:
yes - SSH Tectia Server will ignore these operating
system settings:
the login restriction flag
the unable to login at this time flags (e.g. logintimes)
no (default)
The record-ptyless-sessions attribute can be used
to control whether sessions without PTYs are recorded as user logins in
the operating system. Sessions without PTYs are for example remote
commands and SFTP sessions. By default, all sessions are recorded.
However, some system utilities (such as finger on Solaris) do not allow
sessions without PTYs to be recorded because these sessions do not have a
valid TTY name. On these systems, only real shell logins should be
recorded and others turned off by setting
record-ptyless-sessions=no.
The value must be yes or no.
The default is yes.
The user-config-dir attribute can be used to
specify a directory where user-specific configuration data is to be found,
if the data is not stored in the default location. With this setting, the
administrator can control those options that are usually controlled by the
user. SSH Tectia Server expects Tectia-style directory structure under the given directory,
for example, the /authorized_keys directory, and the
/authorization file, if they are being used.
For user-config-dir, the default is %D/.ssh2.
The directory path can include pattern strings which will be expanded by
SSH Tectia Server. The following pattern strings can be used:
%D or %homedir% is the user's
home directory
%U or %username% is the user's
login name
For Windows domain users, these strings are substituted differently:
%U is expanded to domain.username
%username% is expanded to domain\username
%IU or %userid% is the user's
user ID (uid) (Unix only)
%IG or %groupid% is the user's
group ID (gid) (Unix only)
On Unix, the default-path attribute can be used to
define the default PATH value for the user environment. This path will
be applied after connection to a server unless anything else is defined
in the system settings. Alternatively, the default environment can be set
by using the environment variable PATH.
On Windows, the windows-logon-type attribute can be used to define
what kind of user logon methods for the local host are accepted by SSH Tectia Server.
The defined logon type affects password authentication.
This attribute takes values batch, interactive, network,
and network-cleartext. The default value is
interactive.
For example, to enable accounts that do not have the access right to log on locally, make the following setting:
<settings windows-logon-type="network" />
For information on the attribute values, refer to Microsoft documentation on the Windows logon types.
On Windows, the windows-terminal-mode attribute can be
used to define the mode of operation of a terminal session on the server
side. This attribute takes values console and
stream.
If set to console (default), the server
reads the screen buffer in a loop and detects modifications based on
current cursor location. If set to stream, the server
reads the stdout and stderr of cmd.exe as a stream of
data, while providing basic facilities for command-line editing.
On Linux and Solaris, the ignore-nisplus-no-permission
attribute can be used to define whether SSH Tectia Server should ignore it if NIS+
gives no permission to the user during authentication. The value can be
yes or no. The default is no.
When set to yes, and when the user to authenticate
is not root, the server will ignore it if the NIS+ returns *NP* when
querying for shadow password. *NP* indicates no permission to read the
password information.
| Note |
|---|---|
When NIS+ returns *NP*, the user will NOT be able to use password authentication or the keyboard-interactive with password authentication to authenticate the session. However, the keyboard-interactive with PAM is possible. |
The quiet-login attribute can be used to define
whether to suppress the messages about last login, password expiry,
messages of the day and other such information during login. This can be
useful in case third-party applications are used to launch a shell, and the
messages are useless or even confusing to the applications. The attribute
value can be yes or no. The default is
no.
Example of the settings element and its attributes:
<settings proxy-scheme="direct:///10.0.0.0/8,localhost;socks5://fw.example.com:1080/" xauth-path="/usr/X11R6/bin/xauth" ignore-aix-rlogin="no" ignore-aix-login="no" record-ptyless-sessions="yes" user-config-dir="%D/.ssh2" default-path="" windows-logon-type="interactive" windows-terminal-mode="console" ignore-nisplus-no-permission="no" quiet-login="no" />
Example of the settings needed when you want to suppress any messages of the day (MOTDs), last-login messages or warnings about password expiration:
<settings xauth-path="/usr/X11R6/bin/xauth" windows-logon-type="interactive" quiet-login="yes" />
This element can be used to define defaults for PAM account management and session management with the following attributes:
The pam-calls-with-commands attribute
defines whether PAM Account Management (pam_acct_mgmt) and PAM Session
Management (pam_session_mgmt) are enabled when the user executes shells,
remote commands and subsystems. The values are yes and
no. The default is no, which disables
PAM session and account management. This setting has no effect on
platforms which do not support PAM.
Enabling pam-calls-with-commands will enforce the
PAM restrictions on session and account management regardless of the
authentication method that is used to connect to the server. Note that
this requires either a PAM configuration file for the service
ssh-server-g3 or the use of the service-name
attribute to specify the service used by PAM.
The service-name attribute can be used
to instruct PAM about which configuration it should use. When defined,
this setting will override the factory setting which is
ssh-server-g3. Note that it is possible to define
different service names for user session management and for
authentication by defining different values for the
service-name attribute in the
pluggable-authentication-modules element and in the
submethod-pam element.
Attribute dll-path can be used to
define the location of the PAM library, if the library is not in the
default library path of the operating system.
If the PAM library is not in the default library path then the
dll-path attribute is needed both here in
pluggable-authentication-modules and in the
authentication-methods setting
submethod-pam.
The settings made in pluggable-authentication-modules
can be overriden locally by adding PAM-related settings also to the
authentication-methods block.
Under the auth-keyboard-interactive element you can define
the submethod-pam element with attributes
service-name and dll-path.
With the following example configuration, the factory settings are
overriden by defining sshd2 as the service for PAM
(in the pluggable-authentication-modules setting).
This service will be used by ssh-user-exec, for
example. To make the PAM submethod to use the ssh-server-g3
service, it is specified with the service-name in the
submethod-pam setting.
<params>
<pluggable-authentication-modules service-name="sshd2"/>
</params>
<!-- ... -->
<authentication-methods>
<authentication action="allow" name="allow-default">
<auth-keyboard-interactive>
<submethod-pam service-name="ssh-server-g3" />
</auth-keyboard-interactive>
</authentication>
</authentication-methods>
This element defines the location of the private host key and optionally the location of the public key and/or certificate. The elements inside the element must be given in the right order (private key before public).
Inside one hostkey element either the public key
or the certificate can be given, not both.
Giving the public key in the configuration file is not mandatory. It will be derived from the private key if it is not found otherwise. However, specifying the public key will decrease the start-up time for the software, as deriving the public key is a fairly slow operation.
The private element gives the path to the private key file as a value of the
file attribute.
The key file should be located on a local drive. Network
or mapped drives should not be used, as the server program may
not have proper access rights for them. The default is
hostkey, in the /etc/ssh2
directory on Unix and in the
"C:\Program Files\SSH Communications Security\SSH Tectia\SSH Tectia Server" directory on Windows.
On Unix, the private key file should be readable and writable only
by root. The private key directory should be writable
only by root.
On Windows, the key file and directory should have full permissions for the Administrators group and the SYSTEM account and no other permissions.
This element gives the path to the public key file as a value
of the file attribute.
The key file should be located on a local drive. Network or mapped drives should not be used, as the server program may not have proper access rights for them.
Alternatively, the public key can be specified as a base64-encoded ASCII element.
This element gives the path to the X.509 user certificate file as
a value of the file attribute.
Alternatively, the certificate can be specified as a base64-encoded ASCII element.
This element defines an external host key. The
type must be given as an attribute. The currently
supported types are none, software,
entrust, mscapi, pkcs11,
and pkcs12.
The init-info for the external key can also be given.
Sample hostkey elements are shown below:
<hostkey>
<private file="/etc/ssh2/hostkey_dsa" />
<public file="/etc/ssh2/hostkey_dsa.pub" />
</hostkey>
<hostkey>
<private file="/etc/ssh2/hostcert_rsa" />
<x509-certificate file="/etc/ssh2/hostcert_rsa.crt" />
</hostkey>
<hostkey>
<externalkey type="entrust"
init-info="profile-file(/etc/ssh2/hostcertprofile.epf)" />
</hostkey>
For PKCS#12, the <hostkey> settings are as follows:
<hostkey>
<externalkey type="software"
init-info="key_file(/etc/ssh2/server-cert.p12)
key_passphrase_file(/etc/ssh2/my-passphrase)" />
</hostkey>
In the PKCS#12 sample output, the hostkey setting reads the
PKCS#12 file server-cert.p12 and if it needs a passphrase
to open it, it will read the my-passphrase file and use the
contents as the passphrase. The file can also contain additional
certificates but they are ignored in SSH Tectia Server.
In the init-info string, the following keywords are
supported:
directory(<directory_name>) - defines the directory
to be polled for the keys. All files in the named directory are added to
sshexternalkey. Note however, that this option lacks control
over the actual server key and certificate.
polling_interval_ms(<time_ms>) - defines the polling
interval for the option above.
key_files(<key_spec>) - defines that multiple
comma-separated files are read. Loose grouping between files is expected so
that public key, private key and certificate are assumed to be parts of the
same key. Supported in SSH Tectia Server.
key_file(<file_name>) - defines that one key file
is read. The same as key_files with one parameter.
key_passphrase(<passphrase>) - if a private key or
certificate container is password-protected, the command tries to open it
with the supplied passphrase first. In case the passphrase is not valid,
the authentication callback is called normally. In the server, that means a
failure to open the file as the server does not have an interactive prompt.
key_passphrase_file(<filename>) - defines that
instead of giving the passphrase in the configuration file directly, it can be
written to a separate file. This option is useful if server configuration file
needs to be more widely readable. The private key and passphrase can still be
with root access only.
This element is used to specify where the Secure Shell server
listens for connections. The element has three attributes:
id, address, and port.
The id must be given as an attribute. The value must be
unique. The value must begin with a letter, it can contain alphanumeric
characters or underscore characters but no any whitespaces. Also the
port and network interface address can be given.
The default port for listeners is 22.
Several listeners can be created to the same IP address to different ports. Each must have an unique ID. If the address is not specified, the server will listen to the given port on all interfaces.
Sample listener elements are shown below:
<listener id="internet" address="192.0.2.62" /> <listener id="intranet" address="10.0.0.1" /> <listener id="admin-private" port="222" />
On Windows, you can add this optional domain-policy setting to
define how SSH Tectia Server will handle user names when a user logs in without
specifying the prefix (indicating local or domain user). This setting
defines where the server will look for the user account, and how it will
fill in the missing prefix part.
The windows-domain-precedence element defines a
comma-separated list of trusted domains and special values
%default% and %local%.
The list is read in order, and the first domain that has an account for the
user name will be used to log in the user and the rest will be ignored. If
the user name is not found in any of the specified domains, the user account
is assumed not to exist.
Value %local% means that a user
without a specified prefix will be treated as a local user
(username → localmachine_name\username).
Value %default% means that a user
without a specified prefix will be treated as a domain user, and the domain
name is expected to be the default domain of the local machine
(username → defaultdomain_name\username).
If this setting is not defined in the SSH Tectia Server configuration, and a user logs in without specifying the prefix, SSH Tectia Server first checks if the given user name is valid in the default domain where the local machine exists. If no match is found, for example because the machine is standalone, the user will be treated as a local user.
A sample domain-policy setting is shown below:
<domain-policy windows-domain-precedence="%local%, %default%, domainA, domainB" />
This element changes the logging settings that define the
log event severities and logging facilities. The element contains
one or more log-events elements.
This element sets the severity and facility of different logging events. The events have reasonable default values, which are used if no explicit logging settings are made. This setting allows customizing the default values.
For the events, facility and
severity can be set as attributes. The events
itself should be listed inside the log-events
element.
The facility can be normal, daemon,
user, auth, local0,
local1, local2, local3,
local4, local5, local6,
local7, or discard. Setting the
facility to discard causes the server to ignore
the specified log events.
On Windows, only the normal and
discard facilities are used.
The severity can be informational,
notice, warning, error,
critical, security-success, or
security-failure.
Any events that are not specifically defined in the
configuration file use the default values. The defaults
can be overridden for all remaining events by giving an empty
log-events element after all other definitions
and setting a severity value for it.
For a complete list of log events, see Appendix C.
The following example sets the facility of the
Auth_method_failure event to auth and the
severity to notice. It also sets the facility of the
Server_reconfig_started and Server_starting
events to discard (the events will not be logged). All other
events use the default settings.
<logging>
<log-events facility="auth" severity="notice">
Auth_method_failure
</log-events>
<log-events facility="discard">
Server_reconfig_started Server_starting
</log-events>
</logging>
This element sets the maximum number of connections and processes the server will handle. SSH Tectia Server uses a distributed architecture where the master server process launches several servant server processes that handle the actual connections.
The max-processes attribute defines the maximum
number of servant processes the master server will launch. The value
range is 1-40. The default value is 40.
The max-connections attribute defines the
maximum number of client connections allowed per servant. The value
range is 1-256. The default value is 256.
This setting is useful in systems with low resources. The server has to be restarted to use the changed setting.
A sample limits element is shown below:
<limits max-connections="256" max-processes="40" />
This element contains the CA certificates used in validation of the
host-based and public-key authentication certificates. The element can
have the following attributes: http-proxy-url,
socks-server-url, cache-size,
max-crl-size, external-search-timeout,
max-ldap-response-length, and ldap-idle-timeout.
The http-proxy-url attribute
defines a HTTP proxy and the socks-server-url
attribute defines a SOCKS proxy for making LDAP or OCSP queries for
certificate validity.
The address of the proxy is given as the value of the attribute. The
format of the address is
socks://username@socks_server:port/network/netmask,network/netmask
... (with a SOCKS proxy) or
http://username@proxy_server:port/network/netmask,network/netmask
... (with an HTTP proxy).
For example, by setting socks-server-url to
"socks://mylogin@socks.ssh.com:1080/192.168.0.0/16,10.100.23.0/24",
the host socks.ssh.com and port 1080
are used as your SOCKS server for connections outside of
networks 192.168.0.0 (16-bit domain) and
10.100.23.0 (8-bit domain). Those networks are
connected directly.
The cache-size attribute defines the maximum size
(in megabytes) of in-memory cache for the certificates and CRLs. The
allowed value range is 1 to 512; and the default value is 35 MB.
The max-crl-size attribute defines the maximum size
(in megabytes) of CRLs accepted. Processing large CRLs can consume a
considerable amount of memory and processing power, so in some environments
its advisable to limit their size. The allowed value range is 1 to 512; and
the default value is 11 MB.
The external-search-timeout attribute defines the
time limit (in seconds) for external HTTP and LDAP searches for CRLs and
certificates. The allowed value range is 1 to 3600 seconds; and the
default value is 60 seconds.
The max-ldap-response-length attribute defines the
maximum size (in megabytes) of LDAP responses accepted. The allowed value
range is 1 to 512; and the default value is 11 MB.
The ldap-idle-timeout attribute defines an idle
timeout for LDAP connections. The validation engine retains LDAP
connections and reuses them in forthcoming searches. The connection is
closed only after the LDAP idle timeout has been reached. The allowed
value range is 1 to 3600 seconds; and the default idle timeout is 30
seconds.
The cert-validation element can contain
sub-elements. You can use maximum one each of
elements cert-cache-file,
crl-auto-update, and dod-pki, and
multiple instances of the other elements.
The validity of a received certificate is checked separately
using each of the defined ca-certificate elements in
turn until they are exhausted (in which case the authentication
fails), or a positive result is achieved. If the certificate is
valid, the connections and authentication-methods
elements determine whether the certificate allows the user to log in
(of course, the correct signature generated by a matching private
key is always required in addition to everything else).
This element specifies an LDAP server address and
port used for fetching CRLs and/or subordinate CA
certificates based on the issuer name of the certificate being
validated. Several LDAP servers can be specified by using
several ldap-server elements.
CRLs are automatically retrieved from the CRL distribution point defined in the certificate to be verified if the point exists.
The default value for port is 389.
This element specifies an OCSP (Online Certificate Status
Protocol) responder service address in URL format
(url). Several OCSP responders can be specified by
using several ocsp-responder elements.
For the OCSP validation to succeed, both the end-entity
certificate and the OCSP responder certificate must be issued by the
same CA. If the certificate has an Authority Info
Access extension with an OCSP Responder URL, it is only used
if there are no configured OCSP responders. It is not used if any
OCSP responders have been configured.
The validity-period in seconds for the OCSP
data can be optionally defined. During this time, new OCSP
queries for the same certificate are not made but the old result
is used.
If an OCSP responder is defined in the configuration file or in the certificate, it is tried first; only if it fails, traditional CRL checking is tried, and if that fails, the certificate validation returns a failure.
This element specifies the name of the file
where the certificates and CRLs are stored when the SSH Tectia Server
service is stopped, and read back in when the service is restarted.
On Unix, the cache file should be writable only by
root.
On Windows, the cache file should be writable only by the Administrators group and the SYSTEM account.
This element turns on automatic updating of certificate
revocation lists. When it is on, SSH Tectia Server periodically tries to
download the new CRL before the old one has expired. The
update-before attribute can be used to specify how many
seconds before the expiration the update takes place. The
minimum-interval sets a limit for the maximum update
frequency. The default minimum interval is 30 seconds.
This element instructs SSH Tectia Server to periodically download a CRL from
the specified url. The url can be an LDAP or
HTTP URL, or it can refer to a local file. The file format must be either
binary DER or base64, PEM is not supported.
To download CRLs from the local file system, define the file URL in this format:
file:///absolute/path/name
To download CRLs from an LDAP, define the LDAP URL in this format:
ldap://ldap.server.com:389/CN=Root%20CA,
OU=certification%20authorities,DC=company,
DC=com?certificaterevocationlistUse the interval attribute to specify how often
the CRL is downloaded. The default is 3600 (seconds).
This element defines whether the certificates are required to
be compliant with the DoD PKI (US Department of Defense Public-Key
Infrastructure). In practice, this means that the Digital
Signature bit must be set in the Key Usage of the certificate. The
enable attribute can have a value of yes
or no. The default is no.
This element enables user authentication using
certificates. It can have four attributes: name,
file, disable-crls, and use-expired-crls.
The name attribute must contain the name of the CA.
The element must either contain the path to the X.509 CA
certificate file as a value of the file attribute,
or include the certificate as a base64-encoded ASCII
element.
CRL checking can be disabled by setting the
disable-crls attribute to
yes. The default is no.
| Note |
|---|---|
CRL usage should only be disabled for testing purposes. Otherwise it is highly recommended to always use CRLs. |
Expired CRLs can be used by setting a numeric value (in
seconds) for the use-expired-crls
attribute. The default is 0 (do not use expired CRLs).
A sample cert-validation element is shown below:
<cert-validation http-proxy-url="http://proxy.example.com:800">
<ldap-server address="ldap.example.com" port="389" />
<ocsp-responder validity-period="60" url="http://ca.example.com/ocsp-1/" />
<cert-cache-file file="/var/cert-cache.dat" />
<crl-auto-update update-before="30" minimum-interval="600" />
<crl-prefetch interval="1800" url="http://ca.example.com/default.crl" />
<dod-pki enable="no" />
<ca-certificate name="exa-ca1" file="/etc/ssh2/exa-ca1.crt" />
<ca-certificate name="exa-ca2" file="/etc/ssh2/exa-ca2.crt"
use-expired-crls="3600" />
<ca-certificate name="testonly-ca" file="/etc/ssh2/testonly-ca.crt"
disable-crls="yes" />
</cert-validation>
connections BlockThe connections block defines the basic rules for
allowing and denying connections. The connections block
includes one or more connection elements.
If a user does not match to any selectors in the
connection elements, the connection is allowed with server
default connection settings.
Each connection element specifies either an allow
or deny rule for connections. The element can have three attributes:
name, action, and tcp-keepalive.
The word allow or deny is given as a
value of the action attribute. By default, if the
action attribute is omitted, the connection is
allowed.
The name attribute can be used to give an identifier to
the connection rule. The value must be a valid XML name beginning with a
letter and containing alphanumeric characters or the underscore character
without any whitespace. The identifier can be used, for example, in
auditing.
The tcp-keepalive attribute defines whether the
system should send keepalive messages to the other side. If they
are sent, a broken connection or crash of one of the machines will
be properly noticed. However, this means that connections will die
if the route is down temporarily, and this can be annoying in some
situations. On the other hand, if keepalive messages are not sent,
sessions may hang indefinitely on the server, leaving "ghost" users
and consuming server resources. The value must be yes
or no. The default is no (do not send
keepalives).
The connection element can include one or more
selectors, a rekey setting, and cipher and MAC definitions.
The selectors define to which connections this connection rule
applies to. Only the interface and ip
selector attributes can be used in the connections
block. Other information, for example the user name, is not yet available
at this stage of the connection. Do not define any other selector
attributes, as their matching process would end in error and terminate
the connection attempt.
See Using Selectors in Configuration File.
This selector matches to the listener interface id or
address and/or port. At least one
attribute must be given. If the id is defined, the
others MUST NOT be given. If the id is not defined,
either or both of address and port may
be given.
This selector matches to an IP address or FQDN
(fully qualified domain name) of the client. Either
address or fqdn can be given, not
both.
The address can be in one of the following formats:
a single IP address x.x.x.x
an IP address range of the form x.x.x.x-y.y.y.y
an IP sub-network mask of the form x.x.x.x/y
The fqdn attribute matches to an FQDN pattern
(case-insensitive). The attribute can include a comma-separated
list of allowed FQDN patterns. These patterns may also contain "*"
and "?" globbing characters.
This element specifies the number of seconds
or transferred bytes after which the key exchange
is done again.
If a value for both seconds and
bytes is specified, rekeying is done whenever one of
the values is reached, after which the counters are reset.
The defaults are 3600 seconds (1 hour) and
1000000000 bytes (~1 GB). The value 0 (zero) turns
rekey requests off. This does not prevent the client from
requesting rekeys.
This element selects a cipher name allowed by
the server for data encryption. The supported ciphers are
3des-cbc,
aes128-cbc,
aes192-cbc,
aes256-cbc,
aes128-ctr,
aes192-ctr,
aes256-ctr,
arcfour,
blowfish-cbc,
twofish-cbc,
twofish128-cbc,
twofish192-cbc,
twofish256-cbc,
crypticore128@ssh.com,
seed-cbc@ssh.com,
and
none (no encryption).
Multiple ciphers can be specified by using multiple
cipher elements. By default, the server allows
3des-cbc,
aes128-cbc,
aes192-cbc,
aes256-cbc,
aes128-ctr,
aes192-ctr,
aes256-ctr,
seed-cbc@ssh.com, and
crypticore128@ssh.com (on Windows and Linux x86).
The ciphers that can operate in the FIPS mode are
3des-cbc,
aes128-cbc,
aes192-cbc,
and
aes256-cbc.
Normally when a specified cipher is not found on the server,
the configuration file reading fails and the server will not
restart. The cipher element may optionally take an
allow-missing attribute, which can have a value of
yes or no. If a value of yes
is given for this attribute and a specified cipher is not found
during configuration reading (for example, CryptiCore on Solaris),
the server logs a warning to the syslog but will restart normally. The
default is no (a missing cipher is treated as fatal
error and the server configuration reading fails).
Setting the allow-missing attribute to
yes is useful when you want to use the same
ssh-server-config.xml file on multiple servers and only
some of the servers have, for example, CryptiCore available.
SSH Tectia Server for Linux on IBM System z automatically uses hardware acceleration with the IBM-provided
cryptographic hardware CPACF, if it is available. Hardware acceleration
is used with the following ciphers:
3des-cbc,
aes128-cbc,
aes192-cbc, and
aes256-cbc.
This element selects a MAC name allowed by the server for
data integrity verification. The supported MAC algorithms are
hmac-md5,
hmac-md5-96,
hmac-sha1,
hmac-sha1-96,
crypticore-mac@ssh.com,
and
none (no data integrity verification).
The hmac-sha1 algorithm can operate in the FIPS mode.
Multiple MACs can be specified by using multiple mac
elements. By default, the server allows
hmac-md5,
hmac-sha1, and
crypticore-mac@ssh.com (on Windows and Linux x86).
Normally when a specified MAC is not found on the server,
the configuration file reading fails and the server will not
restart. The mac element may optionally take an
allow-missing attribute, which can have a value of
yes or no. If a value of yes
is given for this attribute and a specified MAC is not found
during configuration reading (for example, CryptiCore on Solaris),
the server logs a warning to the syslog but will restart normally. The
default is no (a missing MAC is treated as fatal
error and the server configuration reading fails).
Setting the allow-missing attribute to
yes is useful when you want to use the same
ssh-server-config.xml file on multiple servers and only
some of the servers have, for example, CryptiCore available.
SSH Tectia Server for Linux on IBM System z automatically uses hardware acceleration with the IBM-provided
cryptographic hardware CPACF, if it is available. Hardware acceleration
is used with the following MACs:
hmac-sha1,
hmac-sha1-96, and
hmac-sha1-256.
A sample connection element that allows connections
from a specified IP address range is shown below:
<connection name="conn1" action="allow" tcp-keepalive="yes">
<selector>
<ip address="192.168.0.42-192.168.0.82" />
</selector>
<rekey seconds="600" bytes="500000000" />
<cipher name="crypticore128@ssh.com" />
<mac name="crypticore-mac@ssh.com" />
</connection>
A sample connection element that denies all
connections is shown below. As the element does not contain any
selectors, it matches always. This can be used as the last element
in the connections element to deny all connections that
were not explicitly allowed by the previous elements. (By default,
non-matching connections would be allowed.)
<connection action="deny" />
authentication-methods BlockThe authentication-methods block defines the
authentication methods that are allowed and required by the server. It
can have one attribute: login-grace-time. It can contain a
banner-message and an auth-file-modes element
and multiple authentication elements.
The login-grace-time attribute is
used to specify a time after which the server disconnects if the user
has not successfully logged in. If the value is set to 0,
there is no time limit. The default is 600
(seconds).
The authentication methods that are on the same level under one
authentication element are considered allowed (one of them
must succeed).
Several authentication methods can be set as required by nesting the
authentication elements inside each other.
The server allows by default public-key, keyboard-interactive, and password authentication (one of them must succeed).
If the authentication-methods element is empty or
missing from the ssh-server-config.xml file, the server does
not allow any authentication methods and the configuration is essentially
defunctional.
However, if you put inside authentication-methods an
authentication element with no authentication methods
defined, the matching users will be allowed to log in without
authentication. This can be used in combination with selectors and/or
nested authentication methods, but should never be used as the only
authentication element.
![[Caution]](images/caution.gif) | Caution |
|---|---|
Consider carefully before putting an empty
|
This element specifies the path to the message that is sent to
the client before authentication. The path is given as a value of
the file attribute. Alternatively, the banner message
can be given as the contents of the banner-message element.
Note, however, that the client is not obliged to show this message.
<banner-message file="/etc/ssh2/banner-message"> This is the server banner message. If file attribute is set, this inlined text is ignored, and the file is read instead (like in this example). </banner-message>
This element specifies whether SSH Tectia Server on Unix platforms should check permissions and ownership of the user's key files used for public-key authentication.
The word yes or no is given as a
value of the strict attribute. If set to
yes, the permissions and ownership of the
.ssh2 directory, the .ssh2/authorization
file (if used), the .ssh2/authorized_keys directory (if
used), and the keys listed in the authorization file or
present in the authorized_keys directory are
checked.
This is normally desirable because novices sometimes
accidentally leave their directory or files world-writable, in which
case anyone can edit the authorization and key files. The default is
yes.
The mask-bits attribute can be
used to specify the forbidden permission bits in octal format. The
default is 022 (group and others must not have the write
permission).
The ownership of the checked files and directories must be either root or the user.
<auth-file-modes strict="yes" mask-bits="022" />
Each authentication element specifies a chain of
authentication methods. It can include one or more selectors and
different authentication methods. It may also include other
authentication elements.
Defining nesting authentication elements within each other
sets the child elements as required (all must be passed
for the authentication to be successful). Setting multiple authentication
methods at the same level sets them as optional (one
of the methods must be passed for the authentication to be
successful).
The authentication elements are read in top-down order.
For elements on the same level, the first matching element is used and the
remaining elements are ignored. If the element has nested child elements,
they are matched next using the same procedure.
In the authentication element, the action
attribute takes values allow or deny.
The allow value means that users who match a selector will be
allowed into the system. The deny value means that access
will be denied from users who match a selector.
By default, if the action attribute is omitted,
authentication is allowed.
If an authentication chain ends in a deny action, or if
the user does not match to any selectors in the authentication
elements, the user is not allowed to log in.
| Note |
|---|---|
Note that the behavior has changed in SSH Tectia Server 5.1. In SSH Tectia Server 5.0, a non-matching user was allowed the default authentication methods. |
In a nested chain of authentication elements, it is
possible, for example, to set the parent method to deny authentication and
a child element with a selector to allow authentication. If the user
matches the selector and successfully completes the authentication
method(s), login is allowed.
For more information on using authentication chains, see Configuring User Authentication Chains.
The authentication element can take a
repeat-block attribute. This can be used when the
authentication element contains a nested element with
certificate selectors.
Set the value of repeat-block to yes when
you expect the user to have several certificates of which only some allow
login (that is, match the selectors in the child authentication element).
In this case, SSH Tectia Server will try all offered certificates until a match is
found.
If repeat-block is set to no (the
default), SSH Tectia Server will try to match only the first certificate offered by
the client.
The authentication element can additionally take a
set-group attribute, which sets a
group for the users that pass the particular authentication chain. The
group definition can be later used in the services
element.
If set-group is used here, it overrides any
group definitions in the services
element.
See the section called “The services Block”.
The authentication name can be optionally given as an
attribute. The value of name must be a valid XML name
beginning with a letter and containing alphanumeric characters or the
underscore character without any whitespace. The authentication name
can be used, for example, in auditing.
| Caution |
|---|---|
Consider carefully before putting an empty
|
The selectors define to which connections this authentication
method applies to. All selectors can be used in the
authentication-methods block.
See Using Selectors in Configuration File.
This selector defines the information that needs to be matched
in the specified field of user certificates used
in public-key authentication. The information to match is specified in
attribute pattern or regexp (regular
expression). Do not define both in the same selector!
Using this selector requires that the parent element in
the authentication chain contains an auth-publickey
element.
The field can be either ca-list,
issuer-name, subject-name,
serial-number, altname-email,
altname-upn, altname-ip,
altname-fqdn, or extended-key-usage.
The format of the pattern depends on the type of the
field. The ca-list field contains a list of CA
names separated by commas. The names that are defined in the
ca-certificate element are used.
The issuer-name and subject-name
fields contain distinguished names, serial-number
a positive integer. The altname-fqdn
field contains a hostname and altname-ip an IP
address or a range. The altname-email field
contains an email address and altname-upn the
principal name.
The extended-key-usage setting can be used to
define the allowed key purposes for certificates. The main purpose of this
option is to prevent authentication with wrong certificate types, for
example a user certificate should not be accepted for host-based
authentication. In the extended-key-usage field,
add a comma-separated list of standard names or numerical OIDs that
specify which certificate key purposes will be accepted:
Standard name OID Description
------------------------------------------------------------------------------
serverAuth 1.3.6.1.5.5.7.3.1 TLS WWW server authentication
clientAuth 1.3.6.1.5.5.7.3.2 TLS WWW client authentication
ssh-server 1.3.6.1.4.1.2213.15.1.1 SecSH server authentication
(host certificate)
ssh-client 1.3.6.1.4.1.2213.15.1.2 SecSH user authentication
ssh-clientHostbased 1.3.6.1.4.1.2213.15.1.3 SecSH hostbased authentication.
For a configuration example, see the section called “Authentication Examples”.
With extended-key-usage, the explicit
attribute can be used to request that the certificate must include the
key purpose ID specified with the pattern. If this attribute is
not used, any certificate containing no key purpose ID or containing the
anyExtendedKeyUsage definition will be accepted.
For information on anyExtendedKeyUsage and its usage, see
RFC3280, Section 4.2.1.13: Extended Key Usage.
The altname-fqdn, altname-upn,
altname-email, subject-name, and
issuer-name selectors may contain the
%username% keyword which is replaced with the user's
login name before comparing with the actual certificate data.
On Windows, the %username-without-domain% keyword can be
used and it is replaced by the user's login name without the
domain part. The %hostname% keyword can be used in the
same way and it is replaced by the client's FQDN. These
patterns may also contain "*" and "?" globbing
characters.
Patterns are normally matched case-insensitively.
Alternatively, the pattern can be specified using the
pattern-case-sensitive attribute.
In the regexp attribute, you can define a regular
expression to match a range of values in the selected field.
Regular expressions follow the egrep syntax.
For the issuer-name and subject-name selectors, you can also
define if the pattern has to match the subject name completely or only
partly. Use the ignore-prefix attribute to match only
the end of subject name, and the ignore-suffix
attribute to match only the beginning of the subject name. The
ignore options are optional.
You can also define both of the ignore options on simultaneously in
which case the pattern has to match with some point in the subject name.
For example: when both ignore settings are defined on, pattern
O=SSH,OU=*,CN=example matches with:
C=FI, O=SSH, OU=RandD, CN=example, CN=UID12345
The allow-undefined attribute can be used to
control the behavior of the selector when the required certificate
data is not defined (certificates have not been used at all, or the
certificate does not contain the fields to be matched). Its value must
be yes or no.
If set to yes, the undefined data is treated as
non-matched and the matching continues to other elements. The default
is no, (trying to match undefined data results in
termination of the connection).
For more information, see Selectors and Undefined Data.
| Caution |
|---|---|
When creating the certificate selectors, make sure that
every Failing to do this may cause unintended consequences, for example authentication succeeding with many different user names with a single certificate. |
This selector defines the information that needs to be matched
in the specified field of host certificates used
in public-key authentication. The information to match is specified in
attribute pattern or regexp (regular
expression). Do not define both in the same selector!
Using this selector requires that the parent element in
the authentication chain contains an auth-hostbased
element.
The field can be either ca-list,
issuer-name, subject-name,
serial-number, altname-email,
altname-upn, altname-ip,
altname-fqdn, or extended-key-usage.
See details of the field contents under the certificate selector.
Patterns are normally matched case-insensitively.
Alternatively, the pattern can be specified using the
pattern-case-sensitive attribute.
In the regexp attribute, you can define a regular
expression to match a range of values in the selected field.
Regular expressions follow the egrep syntax.
For the issuer-name and subject-name selectors, you can also define if
the pattern has to match the subject name completely or only partly. Use
the ignore-prefix attribute to match only the end of
the subject name, and the ignore-suffix attribute to
match only the beginning of the subject name. Both attributes can be
used together in which case the pattern has to match with some point in
the subject name. The ignore options are optional.
The allow-undefined attribute can be used to
control the behavior of the selector when the required certificate
data is not defined (certificates have not been used at all, or the
certificate does not contain the fields to be matched).
Its value must be yes or no.
If set to yes, the undefined data is treated as
non-matched and the matching continues to other elements. The default
is no, (trying to match undefined data results in
termination of the connection).
For more information, see Selectors and Undefined Data.
This selector matches to the listener interface id or
address and/or port. At least one
attribute must be given. If the id is defined, the
others MUST NOT be given. If the id is not defined,
either or both of address and port may
be given.
This selector matches to an IP address or FQDN (fully qualified
domain name) of the client. Define the information to be matched with
either the address or the fqdn or the
fqdn-regexp attribute, but do not use them together.
The address can be in one of the following formats:
a single IP address x.x.x.x
an IP address range of the form x.x.x.x-y.y.y.y
an IP sub-network mask of the form x.x.x.x/y
The fqdn attribute matches to an FQDN pattern
(case-insensitive). The attribute can include a comma-separated
list of allowed FQDN patterns.
In the fqdn-regexp attribute, you can define a
regular expression to match a range of FQDNs. Regular expressions
follow the egrep syntax.
This selector matches to a user name or ID. Define the
information to be matched with one of the following attributes (do not
use them together): name, id or
name-regexp.
In attribute name, you can define a
comma-separated list of user names.
In attribute id, you can define a
comma-separated list of user IDs.
In attribute name-regexp, you can
define a regular expression to match a range of names.
Regular expressions follow the egrep syntax.
Names are normally matched case-insensitively. Alternatively,
you can define the names to be taken exactly as entered by using
the name-case-sensitive attribute.
In Windows domain environment, the user and
user-group selectors have a length limitation.
For more information, see the description of option
User in
Configuration Tool (Windows).
This selector matches to a user group name or ID. Define the
information to be matched with either the name or
the id or the name-regexp
attribute, but do not use them together.
In attribute name, you can define a
comma-separated list of user names.
In attribute id, you can define a
comma-separated list of user IDs.
In attribute name-regexp, you can define a
regular expression to match a range of user group names. Regular
expressions follow the egrep syntax.
Names are normally matched case-insensitively. Alternatively,
you can define the names to be taken exactly as entered by using
the name-case-sensitive attribute.
In Windows domain environment, the user and
user-group selectors have a length limitation.
For more information, see the description of option
User in
Configuration Tool (Windows).
This selector matches to a privileged user (administrator or root) or to a
non-privileged user. The value can be
yes (match to a privileged user) or no
(match to a normal user).
The allow-undefined attribute can be used to
control the behavior of the selector when the required data is not
defined (user-privilege level is not known).
Its value must be yes or no.
If set to yes, the undefined data is treated as
non-matched and the matching continues to other elements. The default
is no, (trying to match undefined data results in
termination of the connection).
For more information, see Selectors and Undefined Data.
| Note |
|---|---|
On a Windows server, the user-privilege level is not available during the authentication phase when the user is logging in using a domain account and does not yet have an access token allocated. To get the user-privilege status for domain users, the user should first pass password or GSSAPI authentication. If the privilege level needs to be checked for local accounts,
the To check the privilege level of domain accounts on a Windows
server in the |
This selector matches to information in the specified blackboard
field. The information to match can be defined with
attribute pattern or regexp. Do not
define both in the same selector!
During the connection setup phase, the server stores information on the various parameters of the client (for example, IP address, username, certificate fields), which can be later used to allow/deny the connection and set the connection parameters. The information is stored in the so called blackboard fields. The blackboard fields are used as elements inside the selectors.
The most commonly used selector attributes have their own
sub-elements. Custom attributes can be specified with the generic
blackboard sub-element.
Patterns are normally matched case-insensitively.
Alternatively, the pattern can be specified using the
pattern-case-sensitive attribute.
In the regexp attribute, you can define a
regular expression to match a range of values in the selected
field. Regular expressions follow the egrep syntax.
The allow-undefined attribute can be used to
control the behavior of the selector when the required data is not
defined.
Its value must be yes or no.
If set to yes, the undefined data is treated as
non-matched and the matching continues to other elements. The default
is no, (trying to match undefined data results in
termination of the connection).
For more information, see Selectors and Undefined Data.
This selector matches if authentication is passed using a
normal public key (without a certificate). Using this selector
requires that the authentication chain contains an
auth-publickey element.
Optionally, the length range of the public key
can be given as an attribute, for example "1024-2048"
(keys from 1024 to 2048 bits match). The range can also be left
open, for example "1536-" (keys over 1536 bits
match).
The allow-undefined attribute can be used to
control the behavior of the selector when the required data is not
defined (public-key authentication has not been used).
Its value must be yes or no.
If set to yes, the undefined data is treated as
non-matched and the matching continues to other elements. The default
is no, (trying to match undefined data results in
termination of the connection).
For more information, see Selectors and Undefined Data.
On Unix platforms, this selector matches if the user password has
expired and should be changed. The actual password change can be done by
defining a rule with a forced passwd command.
For sample rules, see
the section called “The services Block” and
the section called “Forcing Password Change”.
The allow-undefined attribute can be used to
control the behavior of the selector when the required data is not
defined. Its value must be yes or no.
If set to yes, the undefined data is treated as
non-matched and the matching continues to other elements. The default
is no, (trying to match undefined data results in
termination of the connection).
For more information, see Selectors and Undefined Data.
This element sets the public-key authentication method. The
element can have three attributes: authorization-file,
authorized-keys-directory, and openssh-authorized-keys-file.
The authorization-file attribute can be used to
specify a comma-separated list of paths to files that contain the user
public keys that are authorized for login. The paths can contain pattern
strings that are expanded by SSH Tectia Server.
The following pattern strings can be used:
%D or %homedir% is the user's home directory
%U or %username% is the user's login name
For Windows domain users, these strings are substituted differently:
%U is expanded to domain.username
%username% is expanded to domain\username
%IU or %userid% is the user's user ID (uid)
%IG or %groupid% is the user's group ID (gid)
Note that user ID and group ID are only supported on Unix, not on Windows.
The default is %D/.ssh2/authorization.
The authorized-keys-directory attribute can be
used to specify a comma-separated list of directories that contain the
user public keys that are authorized for login. As above, the paths can
contain pattern strings that are expanded by SSH Tectia Server. The default is
%D/.ssh2/authorized_keys.
The openssh-authorized-keys-file attribute can
be used to specify a comma-separated list of paths to OpenSSH-style
authorized_keys files that contain the user public keys
that are authorized for login. As above, the paths can contain pattern
strings that are expanded by SSH Tectia Server.
SSH Tectia Server looks for a matching public-key in the following locations in the following order:
In the defined authorization file, if such a file exists.
In the defined authorized_keys directory,
if no authorization file is available or the defined file does not include a
matching public-key.
In the defined OpenSSH authorized-keys file, if no matching key was found in the SSH Tectia -related authorization file or key directory.
In the authorization file and then in
the authorized_keys directory located in the directory
defined in user-config-dir in the settings
element, if none of the above locations produced a matching key.
In the default public-key storage location, if none of the previous settings was made.
For more information, see User Authentication with Public Keys.
This element sets the host-based authentication method.
The element can have one attribute:
require-dns-match.
If the require-dns-match attribute is set to
yes, host-based authentication will require the
host name given by the client to match the one found in DNS. If
the hostname does not match, the authentication will fail. The
default is no (exact match not required).
This element sets the password authentication method.
The delay between failed attempts in seconds
(failure-delay) and the maximum number of attempts
(max-tries) can be given as attributes. The default
delay is 2 seconds and default maximum is 3 attempts.
This element sets the keyboard-interactive authentication method.
The delay between failed attempts in seconds
(failure-delay) and the maximum number attempts
(max-tries) can be given as attributes. The default
delay is 2 seconds and default maximum is 3 attempts.
The keyboard-interactive submethods are given as child
elements. The supported methods are submethod-password,
submethod-pam, submethod-securid, and
submethod-radius, and submethod-generic.
If no submethods are configured, all available submethods are allowed by default (however, the server may not be able to find the necessary libraries for SecurID and PAM, for example). If some of the submethods are configured, the rest of the submethods are implicitly disabled.
This element sets the keyboard-interactive PAM submethod in use. PAM is supported on Unix platforms.
The service-name attribute can be used to instructs
PAM about which configuration it should use. When used, this setting will
override the setting in pluggable-authentication-modules.
Note that it is possible to define different service names for
authentication and user session management by defining different
values for the service-name here and in the
pluggable-authentication-modules element.
If you have multiple authentication elements that
have the PAM submethod enabled (for example for different authentication
chains for intranet and Internet users), you can define different
service-name settings for them.
The dll-path can be used to define a non-standard
location for the PAM library, or a comma-separated list of PAM DLLs.
If the PAM library is not in the default library path then the
dll-path attribute is needed both here in
submethod-pam and in the
pluggable-authentication-modules element.
On AIX, the path should include the archive file, unless the library is a shared object or has been extracted from the shared object.
This element sets the keyboard-interactive password submethod in use.
This element sets the keyboard-interactive SecurID submethod in use.
The dll-path to the SecurID DLL can be
given in an attribute. The path must point to the
operating-system specific SecurID module, for example,
"/usr/lib/libaceclnt.so" on Solaris.
This element sets the keyboard-interactive RADIUS submethod in use.
The element can contain multiple radius-server child
elements.
This element defines a RADIUS server. The element
has four attributes: address,
port, timeout, and
client-nas-identifier.
The address is the IP address of the
RADIUS server. The port is the RADIUS server
port. The default port is 1812.
The timeout is the time in seconds
after which the RADIUS query is terminated if no response
is gained. The default is 10 seconds.
The client-nas-identifier attribute defines
the network access server (NAS) identifier to be used when talking
to the RADIUS server.
The element must contain one radius-shared-secret
child element.
This element sets the generic submethod in use. This element can be used to add custom submethods to keyboard-interactive authentication.
The name on the method must be given in the attribute.
Optional params for the submethod can be given as
well.
This element sets the GSSAPI authentication method.
The dll-path can be given as an attribute.
This specifies where the necessary GSSAPI libraries are located.
If this attribute is not specified, the libraries are
searched for in a number of common locations. The full path to
the libraries should be given, for example,
"/usr/lib/libkrb5.so,/usr/lib/libgssapi_krb5.so".
On AIX, the dll-path should include the archive file,
if applicable, for example,
"<path>/libgssapi_krb5.a(libgssapi_krb5.a.so)".
The archive(shared_object) syntax is not necessary if
the library is a shared object or has been extracted from the shared
object.
On Windows, the dll-path attribute is
ignored. SSH Tectia Server locates the correct DLL automatically.
The allow-ticket-forwarding attribute defines
whether the server allows forwarding the Kerberos ticket over
several connections. The attribute can have a value of
yes or no. The default is
no.
Normally if a specified authentication method is not found on the
server, the configuration file reading fails and the server will not
restart. The auth-gssapi element may optionally take an
allow-missing attribute, which can have a value of
yes or no. If a value of yes is
given for this attribute and GSSAPI plugin is not found during
configuration reading, the server logs a warning to the syslog but will
restart normally. The default is no (if GSSAPI is specified
but not found, it is treated as fatal error and the server configuration
reading fails).
Setting the allow-missing attribute to
yes is useful when you want to use the same
ssh-server-config.xml file on multiple servers and only
some of the servers have Kerberos/GSSAPI available.
The authentication elements can be nested within each
other. The method(s) in the child element(s) must be passed in addition to
the method in the parent element.
A sample authentication-methods element is shown below:
<authentication-methods>
<authentication>
<selector>
<user-group name="staff" />
</selector>
<auth-publickey authorized-keys-directory="%IG/ssh2_authorized_keys" />
<auth-password />
</authentication>
</authentication-methods>
In this simple authentication example, the users who belong to group "staff" are allowed to log in using either public-key or password authentication. The user public keys are checked from an alternate location. As there are no other authentication blocks, all users that do not match to the selector are implicitly denied authentication.
| Note |
|---|---|
Note that the behavior has changed in SSH Tectia Server 5.1. In SSH Tectia Server 5.0, a non-matching user was allowed the default authentication methods. |
Another sample authentication-methods element is shown
below:
<authentication-methods>
<authentication action="deny">
<auth-publickey />
<authentication action="allow" set-group="local-user">
<selector>
<ip address="10.1.55.14-10.1.55.99" />
<user name="johnd" />
<user name="janed" />
</selector>
<auth-keyboard-interactive max-tries="4"/>
<submethod-radius>
<radius-server address="10.1.61.128">
<radius-shared-secret file="&configdir;/radius-secret-file"/>
</radius-server>
</submethod-radius>
</auth-keyboard-interactive>
</authentication>
<authentication action="allow" set-group="finance-inspector">
<selector>
<user-group name="finance" />
</selector>
<auth-password />
</authentication>
</authentication>
</authentication-methods>
In the example above, all users are first required to authenticate
using public-key authentication. Based on selector matching, also a
second method needs to be passed (RADIUS via keyboard-interactive or
password). A group is set based on the matched and passed authentication
methods. If a user does not match to either of the child authentication
elements, access is denied (the parent authentication element has
the action set to deny).
If the action of the parent authentication element would be
allow, the non-matching users would be let in after having
passed public-key authentication.
See Configuring User Authentication Chains for more examples of configuring authentication chains.
A sample authentication-methods element that sets
requirements for certificate authentication is shown below:
<authentication-methods>
<authentication action="allow" repeat-block="yes">
<auth-publickey />
<authentication action="allow" set-group="admin">
<selector>
<user-privileged value="yes" allow-undefined="yes" />
<certificate field="ca-list" pattern="exa-ca1,exa-ca2"
allow-undefined="yes" />
<certificate field="subject-name" pattern="C=FI,
O=SSH, OU=*, CN=%username%"
ignore-suffix="yes" allow-undefined="yes" />
</selector>
</authentication>
<authentication action="allow">
<selector>
<publickey-passed length="1024-2048" />
</selector>
</authentication>
<authentication action="deny" />
</authentication>
</authentication-methods>
In the example above, privileged users (administrators) are required to pass certificate authentication and the certificate must contain the correct fields. Other users are allowed to log in using a plain public key of a size from 1024 to 2048 bits.
In this example, the allow-undefined attribute has to be
used in the selectors of the first nested authentication block. Otherwise,
the authentication will end in error for users with plain public keys. When
the user uses a plain public key, the server will not have the certificate
fields to be matched defined. For more
information, see Selectors and Undefined Data.
| Note |
|---|---|
Specifying an explicit |
The following example configuration shows how to define explicitly the certificate types that match the authentication policy:
<authentication-methods>
<authentication action="deny">
<auth-publickey />
<authentication action="allow">
<selector>
<certificate field="extended-key-usage"
pattern="clientAuth,ssh-client"
explicit="yes" />
</selector>
</authentication>
</authentication>
</authentication-methods>
This example configuration denies public-key authentication, and accepts
only certificates that include either one or both of the clientAuth
and ssh-client key types.
explicit="yes" defines that the specified key purpose ID must
be matched in the certificate, and so certificates with anyExtendedKeyUsage
(or a missing key purpose ID) will not match.
services BlockThe services block defines the policy for the various
services the server offers.
The services block contains one or more rules
(rule) and optionally defines groups (group).
Creates a group that can be used as a basis for restricting services. Groups are defined based on selectors.
The name must be given as an attribute.
The value of name must be a valid XML name beginning with a
letter and containing alphanumeric characters or the underscore character
without any whitespace.
If the user was already put to a group during authentication
using the set-group attribute, the group definitions in
the services element are ignored.
The selectors define the users that belong to the group. The same
selectors can be used as in the authentication-methods
block.
See Using Selectors in Configuration File and
the section called “The authentication-methods Block”.
Sample group elements are shown below:
<!-- Remote access. -->
<group name="remote-access">
<selector>
<interface address="192.0.2.62" />
</selector>
</group>
<!-- Backup. -->
<group name="backup">
<selector>
<user name="backup" />
</selector>
</group>
<!-- Password change needed. -->
<group name="passwd-change">
<selector>
<user-password-change-needed />
</selector>
</group>
This element defines a rule for the specified
group of users. Rules can be used to restrict the
services and commands the server allows to the users. The element
can have three attributes: group, idle-timeout,
and print-motd.
The rules are read in order, and the first rule that matches
the user's group is used. The match must be exact. No
wildcards are allowed in the group attribute. If no
group is specified, the rule matches to all users.
The idle-timeout attribute sets the idle
timeout limit in seconds. If the connection (all channels) has been
idle this long, the connection is closed. The default is
0 (zero), which disables idle timeouts.
The print-motd attribute defines
whether the message of the day (/etc/motd) is printed
when a user logs in interactively to a Unix server. The value must be
yes or no. The default is yes.
Each rule can contain environment,
terminal, subsystem, tunnel-agent,
tunnel-x11, tunnel-local, tunnel-remote,
and command elements.
An empty rule allows the specified group to perform all actions.
| Note |
|---|---|
The default (unnamed) rule allows all users access to all services. Keep the default rule as the last rule, so it will match to users that are not set in any group. Remember to edit the rule according to your security policy. |
This element defines the environment variables the user
group is allowed to set at the client side. The variables are given in
the allowed attribute as a comma-separated list. By
default, the user can set the TERM, PATH,
TZ, LANG, and LC_*
variables.
Do not use * (asterisk), as it will allow any and all variables, and that can be a security risk.
Allowed variables are normally matched case-insensitively.
If case-sensitive variables are needed, specify them using the
allowed-case-sensitive attribute.
This element defines whether terminal access is allowed or denied for
the user group. The word allow or deny
can be given as the value of the action attribute.
By default, terminal access is allowed.
On Unix systems, the chroot attribute can be
optionally used to define a directory where the user is chrooted during
the terminal session. For more information on
chrooting, see Chrooting (Unix).
If terminal access is denied, also shell commands are denied,
unless commands are explicitly allowed or set as forced by the
command element. See
command.
This element defines a subsystem. The element can take the following
attributes:
type, action, audit (optional),
exec-directly (optional), application (optional),
and chroot (optional).
The type attribute must be given. It defines the
subsystem, for which the settings are made. For example sftp.
The action attribute defines whether the use of the
subsystem is allowed or denied. The possible values are
allow and deny. The default is
allow.
| Note |
|---|---|
Denying the SFTP subsystem denies both SFTP and SCP2 operations to the server, but it does not deny OpenSSH-style SCP operations. To deny OpenSSH SCP, you should restrict remote commands. See also command. |
The optional audit attribute can be used to define
whether the audit messages of the subsystem are recorded in the system
log. Possible values are yes and no. The
default is yes. The audit attribute can be
used only with the SFTP subsystem.
On Unix, the optional exec-directly attribute can be
used to define that the subsystem is launched directly, instead of using
the user's default shell. Setting this attribute to yes will
allow the use of the subsystem even if the shell defined for the user
account prevents login or command execution (for example:
/bin/false or /bin/nologin).
The default is no.
An example configuration:
<subsystem type="sftp" action="allow" audit="no" exec-directly="yes" />
The optional application attribute can be used to
define the executable of the subsystem. This attribute is not necessary
with the SFTP subsystem if the SFTP binary is in the default location.
Example setting:
<subsystem type="sftp" application="sft-server-g3.exe" action="allow" />
On Unix, the optional chroot attribute can be
used to define a directory where the user is chrooted when running
the subsystem. For more information on
chrooting SFTP, see Chrooting SFTP.
The element can contain multiple attribute child
elements.
This element defines an attribute of a subsystem.
The name must be given as an attribute.
The value can be optionally given.
This can be used, for example, on Windows platforms to set the user home directory and virtual folders for SFTP.
<subsystem type="sftp" application="sft-server-g3.exe"> <attribute name="home" value="%USERPROFILE%" /> </subsystem>
For more information, see Defining SFTP Virtual Folders (Windows).
This element defines a shell command as allowed, denied,
or forced. The element can have four attributes, however, all of
them are not used at the same time: action,
application, application-case-sensitive,
and chroot.
The value of the action attribute can be
either allow, deny, or
forced. The default is allow.
If the deny action is set, all shell commands are
denied and no further attributes should be specified. Commands are also
denied if terminal access is denied in the rule and the command element
is omitted.
For the allow action, the application
can be optionally specified as an attribute. When the allow
action is set and the application attribute is specified,
running the specified application(s) is allowed and all other
applications are implicitly denied. If the application is not given,
running all commands is allowed.
For the forced action, the application
must be given as an attribute. When the forced action is
set, the specified application is run automatically when the user logs
in successfully, instead of the application the user is trying to run.
All other applications are implicitly denied.
If the terminal element is omitted from the rule and
the command element specifies a forced command, terminal is
implicitly denied. If the user requests a shell, the forced command is
run instead.
If the terminal is explicitly allowed in the rule,
the forced action of the command element
applies only when the user tries to run remote commands. If the user
requests a shell, he can get it normally and the forced command is not
run.
If the SFTP subsystem is allowed, the user can also
use the scp2/scpg3 and
sftp2/sftpg3 programs normally. However, if the SFTP
subsystem is denied, trying to use it will not cause the forced command
to be run, but gives an error message.
| Note |
|---|---|
Support for legacy OpenSSH SCP in SSH Tectia Server is implemented using a command called scp1-compat-srv. When a client uses OpenSSH SCP to connect to SSH Tectia Server, the server invokes this command. Restrictions on remote commands apply also to OpenSSH-style SCP operations to the server. |
Users can also define forced commands for public keys in their
authorization files or OpenSSH-style
authorized_keys files. However, if a command is defined in
the ssh-server-config.xml file, it overrides any commands
defined in the authorization or authorized_keys
files. For more information, see
the section called “Authorization File Options”.
Applications are normally matched case-insensitively.
Alternatively, the application can be specified using the
application-case-sensitive attribute.
On Unix systems, the chroot attribute can be
optionally used to define a directory where the user is chrooted when
running the command. For more information on chrooting,
see Chrooting (Unix).
This element defines whether agent tunneling (forwarding) is allowed or denied by the server.
The word allow or deny can be
given as the value of the action attribute. By
default, agent forwarding is allowed.
For more information on agent forwarding, see Agent Forwarding (Unix).
This element defines whether X11 tunneling (forwarding) is allowed or denied by the server.
The word allow or deny can be
given as the value of the action attribute. By
default, X11 forwarding is allowed.
For more information on X11 forwarding, see X11 Forwarding (Unix).
This element defines a rule for local TCP tunnels (port forwarding). There can be several of these rules. When a user attempts tunneling, the rules are read in order and the first matching rule is used. For details, see the section called “Tunneling Rule Processing”.
The word allow or deny can be
given as the value of the action attribute. By
default, local tunnels are allowed.
Tunneling restrictions can be further defined with the
src and dst elements.
This selector element specifies source address(es) and FQDN(s) for local tunnels.
Define the pattern to be matched with attribute address
or fqdn or fqdn-regexp, but do not use them together.
The address can be in one of the following formats:
a single IP address x.x.x.x
an IP address range of the form x.x.x.x-y.y.y.y
an IP sub-network mask of the form x.x.x.x/y
The fqdn attribute matches to an FQDN pattern
(case-insensitive). The attribute can include a comma-separated
list of allowed FQDN patterns. These patterns may also contain "*"
and "?" globbing characters.
In the fqdn-regexp attribute, you can define a
regular expression to match a range of FQDNs. Regular expressions
follow the egrep syntax.
This element defines destination address(es) and port(s) for local tunnels.
The address or the fqdn (not
both) can be given as an attribute. Also the port
can be given.
The address can be in one of the following formats:
a single IP address x.x.x.x
an IP address range of the form x.x.x.x-y.y.y.y
an IP sub-network mask of the form x.x.x.x/y
The fqdn attribute matches to an FQDN pattern
(case-insensitive). The attribute can include a comma-separated
list of allowed FQDN patterns. These patterns may also contain "*"
and "?" globbing characters.
In the fqdn-regexp attribute, you can define a
regular expression to match a range of FQDNs. Regular expressions
follow the egrep syntax.
The port attribute can specify a single port or a
port range (for example, 2000-9000).
For more information on local tunnels, see Local Tunnels.
This element defines a rule for remote TCP tunnels (port forwarding). There can be several of these rules. When a user attempts tunneling, the rules are read in order and the first matching rule is used. For details, see the section called “Tunneling Rule Processing”.
The word allow or deny can be
given as the value of the action attribute. By
default, remote tunnels are allowed.
Tunneling restrictions can be further defined with the
src and listen elements.
This selector element specifies source address(es) and port(s) for remote tunnels.
Define the pattern to be matched with attribute address
or fqdn or fqdn-regexp, but do not use them together.
The address can be in one of the following formats:
a single IP address x.x.x.x
an IP address range of the form x.x.x.x-y.y.y.y
an IP sub-network mask of the form x.x.x.x/y
The fqdn attribute matches to an FQDN pattern
(case-insensitive). The attribute can include a comma-separated
list of allowed FQDN patterns. These patterns may also contain "*"
and "?" globbing characters.
In the fqdn-regexp attribute, you can define a
regular expression to match a range of FQDNs. Regular expressions
follow the egrep syntax.
This element defines listen address(es) and port(s) for remote tunnels.
The address and the port can
be given as attributes.
The address can be in the formats described
above for the src element.
The port attribute can specify a single port or a
port range (for example, 2000-9000).
For more information on remote tunnels, see Remote Tunnels.
Sample rule elements are shown below:
<!-- Administrators are allowed to do anything. -->
<rule group="admin" />
<!-- The finance inspector. -->
<rule group="finance-inspector" print-motd="no">
<tunnel-local action="allow">
<!-- Microsoft SQL ports. -->
<dst fqdn="finance-db.example.com" port="1433" />
<dst fqdn="finance-db.example.com" port="1434" />
</tunnel-local>
<tunnel-remote action="deny" />
<!-- Can execute commands and shells, as no overriding behavior is defined. -->
</rule>
<!-- Remote access. -->
<rule group="remote-access" idle-timeout="600">
<!-- Setting terminal action to "deny" also denies shell commands,
unless they are specifically allowed. -->
<terminal action="deny" />
<subsystem type="sftp" application="sft-server-g3" chroot="%homedir%" />
<!-- The listed local tunnels are allowed, other local tunnels are
denied. -->
<tunnel-local action="allow">
<!-- IMAP. -->
<dst fqdn="imap.example.com" port="143" />
<dst fqdn="imap.example.com" port="993" />
<!-- POP. -->
<dst fqdn="mail.example.com" port="109" />
<dst fqdn="mail.example.com" port="110" />
<dst fqdn="mail.example.com" port="995" />
</tunnel-local>
<tunnel-remote action="deny" />
</rule>
<rule group="backup">
<terminal action="deny" />
<!-- This account is only used to back up the disk drive. -->
<command application="dd if=/dev/hda" action="forced" />
<tunnel-local action="deny" />
<tunnel-remote action="deny" />
</rule>
<!-- This rule is used to force password change. -->
<rule group="passwd-change">
<terminal action="deny"/>
<subsystem type="sftp" application="sft-server-g3" action="deny" />
<command application="/usr/bin/passwd" action="forced" />
<tunnel-local action="deny" />
<tunnel-remote action="deny" />
</rule>
<!-- The default rule, used if the user has not been put to any group. -->
<rule>
<!-- The listed environment variables are allowed and all others are
denied. There is no "denied" setting. -->
<environment allowed-case-sensitive="TERM,PATH,TZ,LANG,LC_*" />
<terminal action="deny" />
<subsystem type="sftp" application="sft-server-g3" chroot="%homedir%" />
<!-- Only the date command is allowed. Other commands are denied. -->
<command application="date" action="allow" />
<tunnel-local action="allow" />
<tunnel-remote action="deny" />
</rule>
On Unix, the Server default configuration includes settings for forcing the users to change expired passwords.
When users whose passwords have expired attempt to login, the settings
in <rule group="passwd-change"> are applied to them. The
passwd-change group settings deny all services and force the user to enter a
new password.
<!-- This rule is used to force password change. --> <rule group="passwd-change"> <terminal action="deny"/> <subsystem type="sftp" application="sft-server-g3" action="deny" /> <command application="/usr/bin/passwd" action="forced" /> <tunnel-local action="deny" /> <tunnel-remote action="deny" /> </rule>
Note that the user needs an ssh2/sshg3 terminal client to
be able to change the password.
In case you start creating a configuration from scratch, you need to
manually add a rule for handling expired passwords. Make sure you do not
accidentally allow any services for users who are directed to the passwd-
change group after their password has expired. You can use the
ssh-server-config-example.xml settings as a model.
The tunneling rules defined by the tunnel-local and
tunnel-remote elements operate in the same way as selectors.
Inside a tunnel rule, elements of different type are in AND relation to each
other. If a tunnel rule contains several items of the same type, they are in
OR relation to each other.
For example, the following rule matches if both the listen port and the source FQDN match:
<rule>
<tunnel-remote action="allow">
<listen port="1-9000" />
<src fqdn="trusted.example.com" />
</tunnel-remote>
...
</rule>
For example, the following rule matches if either of the source addresses match:
<rule>
<tunnel-remote action="deny">
<src address="192.168.23.1" />
<src address="10.1.0.1" />
</tunnel-remote>
...
</rule>
With several tunneling rules of the same type, the first matching rule
is used. For example, the following configuration allows local tunnels to
all other addresses in network 192.168.14.0/24 except
192.168.14.21-192.168.14.30:
<rule>
<tunnel-local action="deny">
<dst address="192.168.14.21-192.168.14.30" />
</tunnel-local>
<tunnel-local action="allow">
<dst address="192.168.14.0/24" />
</tunnel-local>
...
</rule>
If the tunnel-local elements were in different order,
tunnels to the whole 192.168.14.0/24 network would be allowed
as any tunneling attempts would match the first (allow) rule
and the second (deny) rule would not be read.
For more examples of tunneling rules, see Chapter 8.
| |
Copyright 
2010 SSH Communications Security Corp.
This software is protected by international copyright laws. All rights reserved.
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