Version: 1.1
Created: July 20, 2005
The following document serves as a guide on how to build and configure Pegasus for SSL support. It also discusses how to utilize a certificate-based infrastructure and configure the Pegasus CIM client.
This guide requires a basic understanding of SSL, OpenSSL, and basic authentication. This guide is intended to help developers and administrators make the right decisions about how to use SSL for their particular application. It is not intended to be a primary source of education on SSL. If you are not familiar with these technologies, consult the sources in the Resources section at the bottom.
Note: In this document, the term "trust" refers only to authentication. It does not imply full trust in the traditional sense, because it does not take into account authorization checks. It remains the responsibility of providers and clients to perform authorization, and therefore establish real trust. Likewise, the term "Trust Store" can be misleading since the "store" is only a source of authentication credentials. Please bear this in mind when documenting recommended deployments or building clients or providers.
To build Pegasus with HTTPS support, you will need to build against the OpenSSL package. The SSL support outlined here has been tested against recent releases of the major versions 0.9.7X and 0.9.8X (most notably, 0.9.7d). Because some versions of 0.9.6X do not contain full support for the security functions that Pegasus utilizes (for example, certificate-based authentication is not fully supported by some versions of 0.9.6X), Pegasus does not officially support major version 0.9.6. See Bugzilla 4048 for more information. Because this is an open source project, the SSL support has been tested with many versions of OpenSSL, but we cannot guarantee it has been tested with every version on every platform. A list of recent OpenSSL releases, and important-to-review security advisories and fixes, can be found on the OpenSSL News page.
After grabbing the OpenSSL source tarball, you need to set the following environment variables before building Pegasus:
It is not recommended to enable this protocol, as there have been many security weaknesses associated with it. Unless you are dealing with very outdated clients, you probably do not need to enable it.
After setting these variables, proceed as normal with the build instructions in the readme file.
To generate a self-signed certificate, you must create a private key, a certificate signing request (CSR), and finally the public x509 certificate. You also need an SSL configuration file that defines the parameters of the Distinguished Name (DN). You can use the one that comes with Pegasus, ssl.cnf in the root directory, or generate your own. For a self-signed certificate, the subject is the same as the issuer. Execute the following commands to create a self-signed certificate. The PEGASUS_ROOT and PEGASUS_HOME have to be set to your respective installation and source directory. You will also need an OpenSSL configuration file. There is a sample configuration file that comes with the OpenSSL package.
After creating the keypair, make sure you protect the information sufficiently by changing permissions on the files and/or directories. The following table shows the recommended privileges:
SSL file | Pegasus Config property | Permissions |
---|---|---|
Private key | sslKeyFilePath | rwx------ |
Public certificate | sslCertificateFilePath | rwxr-xr-x |
Truststore | sslTrustStore | rwxr-xr-x |
CRL store | crlStore | rwxr-xr-x |
The administrator is responsible for ensuring that the above file permissions are set correctly. The administrator should also ensure that all containing directories all the way up to the base directory are not world-writable. Pegasus only checks the following conditions when starting up:
These same file permissions should be used for protecting a client's private key, public key, truststore, and crl store as well.
For more information on generating keys and certificates, consult the OpenSSL HOW-TO documentation.
enableHttpsConnection
This is disabled by default on most platforms. It is recommended that all
remote communication be done over the HTTPS port. However, if you are sending
cleartext passwords over the wire, it is imperative that you only use the
secure port. For added security, the HTTP port can be disabled to prevent
clients from connecting to it. The HTTPS connection is enabled by default only
on the following platforms:
httpsPort
The default setting is 5989, the official WBEM secure port.
sslCertificateFilePath
This is the path to the x509 server certificate. The server certificate may be
a chain in which case the file should contain PEM encoded certificates
beginning with the server certificate and followed by each signing certificate
authority (CA) including the root CA. If the server certificate is a self
signed certificate, the file only contains the self-signed certificate in PEM
format. The certificate cannot be encrypted because there is currently no
mechanism for decrypting the certificate using a user-supplied password. This
property must be defined if enableHttpsConnection is true. Any failure in
finding this file will result in the cimserver failing to start. See
Creating SSL Certificates for more information.
sslKeyFilePath
This is the path to the server's private key. All keys should be at least 1024
bytes long. This property must be defined if enableHttpsConnection is true. Any
failure in finding this file will result in the cimserver failing to start. See
Creating SSL Certificate for more information.
sslClientVerificationMode
This setting controls how the cimserver (i.e. the HTTPS port) is configured.
There are three possible settings: disabled, required, optional. There is no
"right" setting for this property. The default is disabled and it is fine to
leave the setting as disabled if you are going to use basic authentication to
authenticate all client requests. In many applications where a physical person
is there to supply a username and password, basic authentication is sufficient.
Other environments may be heterogeneous, in which case it makes sense to allow
both basic authentication and SSL certificate verification. The setting of this
variable also impacts what happens during the OpenSSL handshake:
sslTrustStore
This setting controls the truststore for the cimserver's HTTPS connection. It
can be either a directory or a single root CA file. When set to a directory, it
is recommended that you use the cimtrust CLI to populate the truststore as
there are strict naming requirements for trusted certificate files. See the
cimtrust & cimcrl CLI section for further information.
sslTrustStoreUserName
This setting is only utilized if the sslTrustStore is a single CA file. It is
not used if the sslTrustStore setting is a directory, but it still must be set
to a valid system user. This is because the validation of the property is done
independently of the sslTrustStore setting. This property represents the valid
OS user that corresponds to the root certificate. All requests authenticated
with a certificate under the root CA will be associated with this user and the
username will be propagated to providers. If applications desire for there to
be a one-to-one correspondence between users and certificates, it is
recommended that each certificate be registered individually using the
cimtrust CLI.
crlStore
This is where the CRL (Certificate Revocation List) store resides. It is
important to note that certificates are checked first against the CRL (if
specified) and then against the server truststore. The cimcrl CLI
should be used for CRL management.
The following questions may be helpful in determining how to configure Pegasus CIM Server.
Should I enable the HTTPS port?
To tell the cimserver to require that all clients be trusted, simply set the
sslClientVerificationMode
property to "required."
To tell the cimserver to trust all clients, set the sslClientVerificationMode
property to "disabled" or "optional".
The SSL verification in Pegasus is independent of any other authentication
mechanism. It can still be utilized when authentication is disabled. When
authentication is enabled, the first line of defense is SSL client
verification. In situations where a
client is not authenticated by SSL because the client sent no certificate and
the setting is "optional", the server will attempt to authenticate the client
via another method of authentication . In this case, the authentication
mechanism specified by the configuration property "httpAuthType" will be used
for remote connections and local authentication will be used for local
connections. In situations where a client is not authenticated by SSL because
the client certificate was invalid, the handshake will be terminated.
Note: Before 2.5.1, in the latter case, authentication would have proceeded in
the same way as if the client had sent no certificate. To enable the legacy
behavior, the compile-time flag PEGASUS_OVERRIDE_SSL_CERT_VERIFICATION_RESULT
should be defined.
See the Configuring the Pegasus CIM Client for SSL section below on how to setup the client's truststore.
A Pegasus CIM client can be configured to use SSL by using a constructor that takes an SSLContext. The construction of the SSLContext is really what controls the behavior of the client during the SSL handshake. Without going into minute details about what happens under the covers, here is a description of the various SSLContext constructor parameters.
Here's a code snippet that shows how to call a client constructor that connects to a server over SSL and can present its own trusted certificate if the server requests it. In this scenario, the client also checks the server certificate against its truststore and specifies an additional callback in addition to the default one (the user-specified callback is optional and can be set to null).
Here's a code snippet that shows how to call a client constructor that connects to a server over SSL and does not possess its own trusted certificate. In this scenario, the client also checks the server certificate against its truststore.
Here are some general guidelines on implementing peer verification for the client:
Because only the above arguments can be passed into the Pegasus SSLContext, there are some limitations in the client configuration:
The following paragraphs concern authorization of users authenticated by certificate on the cimserver's HTTPS port.
It is important to note that SSL certificates are verified during the initial handshake, BEFORE any further authentication takes place. If a certificate fails, the connection can be terminated immediately, resulting in a connection exception. This scenario will occur if the sslClientVerification property is set to "required" and no certificate or an untrusted certificate is sent.
Further authorization checks must be performed when validating the user that is mapped to the certificate. First, the user that is registered to the certificate is validated as a valid system user and a valid cimuser (if the cimuser function has been configured). In the case of a certificate chain, the username authorization starts with the leaf certificate. If it successfully finds a mapping for the leaf certificate, it continues; if there is no username for the leaf certificate, the validation proceeds up to the root certificate. If the root certificate is reached and there is still no mapped username, the authorization fails. Additionally, if Pegasus was configured to use PAM, the pam_acct_mgmt function will be called with the user that is mapped to the certificate. This ensures that any login conditions that would have been placed on a user authenticated via basic authentication are still applied to a user authenticated via certificate. The pam_authenticate method will NOT be called. Lastly, the providers must authorize the user. They receive the username that was mapped to the certificate in the OperationContext.
A provider may request the client's certificate chain information through its provider registration MOF. The "RequestedOperationContextContainers" property of PG_Provider should be set to include the "SSLCertificateChainContainer" value. If a client is authenticated via trusted certificate, then the container will include a certificate for each level in the client's certificate chain, up to a maximum depth of seven.
The behavior of this property is dependent on the overall
CIMOM settings. The "enableHttpsConnection" configuration property must be set
to true for the property to have any effect. Additionally, the
"sslClientVerificationMode" configuration property must be set to either
"required" or "optional". If "required" is specified, then the container will
always be populated. If "optional" is specified, the container will be populated
only if the client is authenticated via trusted certificate, as opposed to
another mechanism such as basic authentication. Because the container may not
always be included in the OperationContext, providers should always check for
its existence before performing operations on it. See the SSLCertificateInfo
class in Pegasus/Common/SSLContext.h for a full list of certificate parameters
that the SSLCertificateChainContainer supports.
The extensions defined for X.509 v3 certificates provide methods for associating additional attributes with users or public keys and for managing the certification hierarchy. Each extension in a certificate may be designated as critical or non-critical. Pegasus relies on the underlying OpenSSL implementation to handle critical extensions specified in a certificate. Please refer to the OpenSSL documentation for more information on currently supported extensions in OpenSSL and on the behavior of OpenSSL in the case of unhandled critical extensions.
For OpenSSL information pick up a copy of O'Reilly's Network Security with
OpenSSL or go to the OpenSSL Site:
http://www.openssl.org
A really fabulous guide on certificate management and installation with OpenSSL:
http://www.gagravarr.org/writing/openssl-certs/index.shtml
x509 Certificate and CRL RFC:
http://www.ietf.org/rfc/rfc2459.txt?number=2459
SSLv3 RFC:
http://wp.netscape.com/eng/ssl3
TLSv1 RFC:
http://www.ietf.org/rfc/rfc2246.txt
Basic Authentication RFC:
http://www.faqs.org/rfcs/rfc2617.html
Copyright (c) 2005 EMC Corporation; Hewlett-Packard Development
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