Apache Tomcat 8

• Quick Start
• Introduction to SSL/TLS
• SSL/TLS and Tomcat
• Certificates
• General Tips on Running SSL
• Configuration
  1. Prepare the Certificate Keystore
  2. Edit the Tomcat Configuration File
• Installing a Certificate from a Certificate Authority
  1. Create a local Certificate Signing Request (CSR)
  2. Importing the Certificate
• Troubleshooting
• Using the SSL for session tracking in your application
• Miscellaneous Tips and Bits

The description below uses the variable name $CATALINA_BASE to refer the base directory against which most relative paths are resolved. If you have not configured Tomcat for multiple instances by setting a CATALINA_BASE directory, then $CATALINA_BASE will be set to the value of $CATALINA_HOME, the directory into which you have installed Tomcat.

To install and configure SSL/TLS support on Tomcat, you need to follow these simple steps. For more information, read the rest of this HOW-TO.

1. Create a keystore file to store the server's private key and self-signed certificate by executing the following command:

   Windows:

   "%JAVA_HOME%\bin\keytool" -genkey -alias tomcat -keyalg RSA

   Unix:

   $JAVA_HOME/bin/keytool -genkey -alias tomcat -keyalg RSA

   and specify a password value of "changeit".

2. Uncomment the "SSL HTTP/1.1 Connector" entry in $CATALINA_BASE/conf/server.xml and modify as described in the Configuration section below.

Transport Layer Security (TLS) and its predecessor, Secure Sockets Layer (SSL), are technologies which allow 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/TLS 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.

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. Details can be found in the Security Considerations Document. 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.

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 passport" for an Internet address. It states which organisation the site is associated with, along with some basic contact information about the site owner or administrator.

This certificate is cryptographically signed by its owner, and is therefore extremely difficult for anyone else to forge. For the certificate to work in the visitors browsers without warnings, it needs to be signed by a trusted third party. These are called Certificate Authorities (CAs). To obtain a signed certificate, you need to choose a CA and follow the instructions your chosen CA provides to obtain your certificate. A range of CAs is available including some that offer certificates at no cost.

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 signed by a well-known CA and are, therefore, not really guaranteed to be authentic at all. While self-signed certificates can be useful for some testing scenarios, they are not suitable for any form of production use.

When securing a website with SSL it's important to make sure that all assets that the site uses are served over SSL, so that an attacker can't bypass the security by injecting malicious content in a javascript file or similar. To further enhance the security of your website, you should evaluate to use the HSTS header. It allows you to communicate to the browser that your site should always be accessed over https.

Using name-based virtual hosts on a secured connection requires careful configuration of the names specified in a single certificate or Tomcat 8.5 onwards where Server Name Indication (SNI) support is available. SNI allows multiple certificates with different names to be associated with a single TLS connector.

To obtain and install a Certificate from a Certificate Authority (like verisign.com, thawte.com or trustcenter.de), read the previous section and then follow these instructions:

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

• 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 <Connector> 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 <Connector> element in the Tomcat configuration file. REMINDER - Passwords are case sensitive!

• When Tomcat starts up, I get an exception like "java.net.SocketException: SSL handshake error javax.net.ssl.SSLException: No available certificate or key corresponds to the SSL cipher suites which are enabled."

  A likely explanation is that Tomcat cannot find the alias for the server key within the specified keystore. Check that the correct keystoreFile and keyAlias are specified in the <Connector> element in the Tomcat configuration file. REMINDER - keyAlias values may be case sensitive!

• My Java-based client aborts handshakes with exceptions such as "java.lang.RuntimeException: Could not generate DH keypair" and "java.security.InvalidAlgorithmParameterException: Prime size must be multiple of 64, and can only range from 512 to 1024 (inclusive)"

  If you are using the APR/native connector, starting with version 1.1.34 it will determine the strength of ephemeral DH keys from the key size of your RSA certificate. For example a 2048 bit RSA key will result in using a 2048 bit prime for the DH keys. Unfortunately Java 6 only supports 768 bit and Java 7 only supports 1024 bit. So if your certificate has a stronger key, old Java clients might produce such handshake failures. As a mitigation you can either try to force them to use another cipher by configuring an appropriate SSLCipherSuite and activate SSLHonorCipherOrder, or embed weak DH params in your certificate file. The latter approach is not recommended because it weakens the SSL security (logjam attack).

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://tomcat.apache.org/lists.html.

This is a new feature in the Servlet 3.0 specification. Because it uses the SSL session ID associated with the physical client-server connection there are some limitations. They are:

• Tomcat must have a connector with the attribute isSecure set to true.
• If SSL connections are managed by a proxy or a hardware accelerator they must populate the SSL request headers (see the SSLValve) so that the SSL session ID is visible to Tomcat.
• If Tomcat terminates the SSL connection, it will not be possible to use session replication as the SSL session IDs will be different on each node.

To enable SSL session tracking you need to use a context listener to set the tracking mode for the context to be just SSL (if any other tracking mode is enabled, it will be used in preference). It might look something like:

package org.apache.tomcat.example;

import java.util.EnumSet;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.SessionTrackingMode;

public class SessionTrackingModeListener implements ServletContextListener {

    @Override
    public void contextDestroyed(ServletContextEvent event) {
        // Do nothing
    }

    @Override
    public void contextInitialized(ServletContextEvent event) {
        ServletContext context = event.getServletContext();
        EnumSet<SessionTrackingMode> modes =
            EnumSet.of(SessionTrackingMode.SSL);

        context.setSessionTrackingModes(modes);
    }

}

Note: SSL session tracking is implemented for the BIO, NIO and NIO2 connectors. It is not yet implemented for the APR connector.

To access the SSL session ID from the request, use:

String sslID = (String)request.getAttribute("javax.servlet.request.ssl_session_id");

For additional discussion on this area, please see Bugzilla.

To terminate an SSL session, use:

// Standard HTTP session invalidation
session.invalidate();

// Invalidate the SSL Session
org.apache.tomcat.util.net.SSLSessionManager mgr =
    (org.apache.tomcat.util.net.SSLSessionManager)
    request.getAttribute("javax.servlet.request.ssl_session_mgr");
mgr.invalidateSession();

// Close the connection since the SSL session will be active until the connection
// is closed
response.setHeader("Connection", "close");

Note that this code is Tomcat specific due to the use of the SSLSessionManager class. This is currently only available for the BIO, NIO and NIO2 connectors, not the APR/native connector.