Tomcat - SSL

Tomcat - SSL Configuration

Overview

Basic steps for configuring SSL support on Tomcat 4 include:
Download JSSE 1.0.2 (or later) and either make it an installed extension on the system, or else set an environment variable JSSE_HOME that points at the directory into which you installed JSSE.
Create a certificate keystore by executing the following command:
$JAVA_HOME/bin/keytool -genkey -alias tomcat -keyalg RSA
and specify a password value of "changeit".
Uncomment the "SSL HTTP/1.1 Connector" entry in $CATALINA_HOME/conf/server.xml and tweak as necessary.
Introduction to SSL

SSL, or Secure Socket Layer, is a technology which allows web browsers and web servers to communicate over a secured connection. This means that the data being sent is encrypted by one side, transmitted, then decrypted by the other side before processing. This is a two-way process, meaning that both the server AND the browser encrypt all traffic before sending out data.

Another important aspect of the SSL protocol is Authentication. This means that during your initial attempt to communicate with a web server over a secure connection, that server will present your web browser with a set of credentials, in the form of a "Certificate", as proof the site is who and what it claims to be. In certain cases, the server may also request a Certificate from your web browser, asking for proof that you are who you claim to be. This is known as "Client Authentication," although in practice this is used more for business-to-business (B2B) transactions than with individual users. Most SSL-enabled web servers do not request Client Authentication.

SSL and Tomcat

It is important to note that configuring Tomcat to take advantage of secure sockets is usually only necessary when running it as a stand-alone web server. When running Tomcat primarily as a Servlet/JSP container behind another web server, such as Apache or Microsoft IIS, it is usually necessary to configure the primary web server to handle the SSL connections from users. Typically, this server will negotiate all SSL-related functionality, then pass on any requests destined for the Tomcat container only after decrypting those requests. Likewise, Tomcat will return cleartext responses, that will be encrypted before being returned to the user's browser. In this environment, Tomcat knows that communications between the primary web server and the client are taking place over a secure connection (because your application needs to be able to ask about this), but it does not participate in the encryption or decryption itself.

Certificates

In order to implement SSL, a web server must have an associated Certificate for each external interface (IP address) that accepts secure connections. The theory behind this design is that a server should provide some kind of reasonable assurance that its owner is who you think it is, particularly before receiving any sensitive information. While a broader explanation of Certificates is beyond the scope of this document, think of a Certificate as a "digital driver's license" for an Internet address. It states what company the site is associated with, along with some basic contact information about the site owner or administrator.

This "driver's license" is cryptographically signed by its owner, and is therefore extremely difficult for anyone else to forge. For sites involved in e-commerce, or any other business transaction in which authentication of identity is important, a Certificate is typically purchased from a well-known certificates can be electronically verified -- in effect, the Certificate so you can believe that that Certificate is valid if you trust the Certificate
In many cases, however, authentication is not really a concern. An administrator may simply want to ensure that the data being transmitted and received by the server is private and cannot be snooped by anyone who may be eavesdropping on the connection. Fortunately, Java provides a relatively simple command-line tool, called keytool, which can easily create a "self-signed" Certificate. Self-signed Certificates are simply user generated Certificates which have not been officially registered with any well-known CA, and are therefore not really guaranteed to be authentic at all. Again, this may or may not even be important, depending on your needs.

General Tips on Running SSL

The first time a user attempts to access a secured page on your site, he or she is typically presented with a dialog containing the details of the certificate (such as the company and contact name), and asked if he or she wishes to accept the Certificate as valid and continue with the transaction. Some browsers will provide an option for permanently accepting a given Certificate as valid, in which case the user will not be bothered with a prompt each time they visit your site. Other browsers do not provide this option. Once approved by the user, a Certificate will be considered valid for at least the entire browser session.

Also, while the SSL protocol was designed to be as efficient as securely possible, encryption/decryption is a computationally expensive process from a performance standpoint. It is not strictly necessary to run an entire web application over SSL, and indeed a developer can pick and choose which pages require a secure connection and which do not. For a reasonably busy site, it is customary to only run certain pages under SSL, namely those pages where sensitive information could possibly be exchanged. This would include things like login pages, personal information pages, and shopping cart checkouts, where credit card information could possibly be transmitted. Any page within an application can be requested over a secure socket by simply prefixing the address with https: instead of http:. Any pages which absolutely require a secure connection should check the protocol type associated with the page request and take the appropriate action of https is not specified.

Finally, using name-based virtual hosts on a secured connection can be problematic. This is a design limitation of the SSL protocol itself. The SSL handshake, where the client browser accepts the server certificate, must occur before the HTTP request is accessed. As a result, the request information containing the virtual host name cannot be determined prior to authentication, and it is therefore not possible to assign multiple certificates to a single IP address. If all virtual hosts on a single IP address need to authenticate against the same certificate, the addition of multiple virtual hosts should not interfere with normal SSL operations on the server. Be aware, however, that most client browsers will compare the server's domain name against the domain name listed in the certificate, if any (applicable primarily to official, CA-signed certificates). If the domain names do not match, these browsers will display a warning to the client user. In general, only address-based virtual hosts are commonly used with SSL in a production environment.

Configuration

Download and Install JSSE

Download the Java Secure Socket Extensions (JSSE) package, version 1.0.2 or later, from http://java.sun.com/products/jsse/. If you built Tomcat from source, you have probably already downloaded this package. If you are running JDK 1.4 (currently in beta), these classes have been integrated directly into the JDK, so you can skip this entire step.

After expanding the package, there are two ways to make it available to Tomcat (choose one or the other):

Make JSSE an installed extension by copying all three JAR files (jcert.jar, jnet.jar, and jsse.jar) into your $JAVA_HOME/jre/lib/ext directory.

Create a new environment variable JSSE_HOME that contains the absolute path to the directory into which you unpacked the JSSE binary distribution.

Prepare the Certificate Keystore

Tomcat currently operates only on JKS format keystores. This is Java's standard "Java KeyStore" format, and is the format created by the keytool command-line utility. This tool is included in the JDK.

To import an existing certificate into a JKS keystore, please read the documentation (in your JDK documentation package) about keytool.

To create a new keystore from scratch, containing a single self-signed Certificate, execute the following from a terminal command line:
$JAVA_HOME/bin/keytool -genkey -alias tomcat -keyalg RSA
(The RSA algorithm should be preferred as a secure algorithm, and this also ensures general compatibility with other servers and components.)

This command will create a new file, in the home directory of the user under which you run it, named ".keystore". To specify a different location or filename, add the -keystore parameter, followed by the complete pathname to your keystore file, to the keytool command shown above. You will also need to reflect this new location in the server.xml configuration file, as described later. For example:
$JAVA_HOME/bin/keytool -genkey -alias tomcat -keyalg RSA \
  -keystore /path/to/my/keystore
After executing this command, you will first be prompted for the keystore password. The default password used by Tomcat is "changeit" (all lower case), although you can specify a custom password if you like. You will also need to specify the custom password in the server.xml configuration file, as described later.

Next, you will be prompted for general information about this Certificate, such as company, contact name, and so on. This information will be displayed to users who attempt to access a secure page in your application, so make sure that the information provided here matches what they will expect.

Finally, you will be prompted for the key password, which is the password specifically for this Certificate (as opposed to any other Certificates stored in the same keystore file). You MUST use the same password here as was used for the keystore password itself. (Currently, the keytool prompt will tell you that pressing the ENTER key does this for you automatically.)

If everything was successful, you now have a keystore file with a Certificate that can be used by your server.

Edit the Tomcat Configuration File

The final step is to configure your secure socket in the $CATALINA_HOME/conf/server.xml file, where $CATALINA_HOME represents the directory into which you installed Tomcat 4. An example <Connector> element for an SSL connector is included in the default server.xml file installed with Tomcat. It will look something like this:
<-- Define an SSL HTTP/1.1 Connector on port 8443 -->

You will note that the Connector element itself is commented out by default, so you will need to remove the comment tags around it. Then, you can customize the specified attributes as necessary. For detailed information about the various options, consult the Server Configuration Reference. The following discussion covers only those attributes of most interest when setting up SSL communication.

The port attribute (default value is 8443) is the TCP/IP port number on which Tomcat will listen for secure connections. You can change this to any port number you wish (such as to the default port for https communications, which is 443). However, special setup (outside the scope of this document) is necessary to run Tomcat on port numbers lower than 1024 on many operating systems.

If you change the port number here, you should also change the value specified for the redirectPort attribute on the non-SSL connector. This allows Tomcat to automatically redirect users who attempt to access a page with a security constraint specifying that SSL is required, as required by the Servlet 2.3 Specification.

You will notice a Factory element nested inside the Connector element. This is where the "socket factory" used by Tomcat, whenever it needs a socket on the corresponding port number, is configured. You may need to add or change the following attribute values, depending on how you configured your keystore earlier:

Attribute Description

className The fully qualified class name of the Java class that implements this socket factory. Do not change the default value.

clientAuth Set this value to true if you want Tomcat to require all SSL clients to present a client Certificate in order to use this socket.

keystoreFile Add this attribute if the keystore file you created is not in the default place that Tomcat expects (a file named .keystore in the user home directory under which Tomcat is running). You can specify an absolute pathname, or a relative pathname that is resolved against the $CATALINA_BASE environment variable.

keystorePass Add this element if you used a different keystore (and Certificate) password than the one Tomcat expects (changeit).

protocol The encryption/decryption protocol to be used on this socket. Do not change the default value.

After completing these configuration changes, restart Tomcat as you normally do, and you should be in business. You should be able to access any web application supported by Tomcat via SSL. For example, try:
https://localhost:8443
and you should see the usual Tomcat splash page (unless you have modified the ROOT web application). If this does not work, the following section contains some troubleshooting tips.

Create a local Certificate Signing Request (CSR)
you have to create a so called Certificate Signing Request (CSR). That CSR will be used as "secure". To create a CSR follow these steps:
Create a local Certificate (as described in the previous section):
keytool -genkey -alias tomcat -keyalg RSA \
	-keystore <your_keystore_filename>
Note: In some cases you will have to enter the domain of your website (i.e. www.myside.org) in the field "first- and lastname" in order to create a working Certificate.
The CSR is then created with:
keytool -certreq -keyalg RSA -alias tomcat -file certreq.csr \
	-keystore <your_keystore_filename>
Importing the Certificate

Now that you have your Certificate you can import it into you local keystore. First of all you have to import a so called Chain Certificate or Root Certificate into your keystore. After that you can procede with importing your Certificate.
For Verisign.com go to: http://www.verisign.com/support/install/intermediate.html
For Trustcenter.de go to: http://www.trustcenter.de/certservices/cacerts/en/en.htm#server
For Thawte.com go to: http://www.thawte.com/certs/trustmap.html
Import the Chain Certificate into you keystore
keytool -import -alias root -keystore <your_keystore_filename> \
	-trustcacerts -file <filename_of_the_chain_certificate>
And finally import your new Certificate
keytool -import -alias tomcat -keystore <your_keystore_filename> \
	-trustcacerts -file <your_certificate_filename>
Troubleshooting

Here is a list of common problems that you may encounter when setting up SSL communications, and what to do about them.

I get "java.security.NoSuchAlgorithmException" errors in my log files.

The JVM cannot find the JSSE JAR files. Follow all of the directions to download and install JSSE.

When Tomcat starts up, I get an exception like "java.io.FileNotFoundException: {some-directory}/{some-file} not found".

A likely explanation is that Tomcat cannot find the keystore file where it is looking. By default, Tomcat expects the keystore file to be named .keystore in the user home directory under which Tomcat is running (which may or may not be the same as yours :-). If the keystore file is anywhere else, you will need to add a keystoreFile attribute to the <Factory> element in the Tomcat configuration file.

When Tomcat starts up, I get an exception like "java.io.FileNotFoundException: Keystore was tampered with, or password was incorrect".

Assuming that someone has not actually tampered with your keystore file, the most likely cause is that Tomcat is using a different password than the one you used when you created the keystore file. To fix this, you can either go back and recreate the keystore file, or you can add or update the keystorePass attribute on the <Factory> element in the Tomcat configuration file. REMINDER - Passwords are case sensitive!

If you are still having problems, a good source of information is the TOMCAT-USER mailing list. You can find pointers to archives of previous messages on this list, as well as subscription and unsubscription information, at http://jakarta.apache.org/site/mail.html".

Attribute	Description
`className`	The fully qualified class name of the Java class that implements this socket factory. Do not change the default value.
`clientAuth`	Set this value to `true` if you want Tomcat to require all SSL clients to present a client Certificate in order to use this socket.
`keystoreFile`	Add this attribute if the keystore file you created is not in the default place that Tomcat expects (a file named `.keystore` in the user home directory under which Tomcat is running). You can specify an absolute pathname, or a relative pathname that is resolved against the `$CATALINA_BASE` environment variable.
`keystorePass`	Add this element if you used a different keystore (and Certificate) password than the one Tomcat expects (`changeit`).
`protocol`	The encryption/decryption protocol to be used on this socket. Do not change the default value.