Links User Guide Reference Apache Tomcat Development | Apache Tomcat 6.0SSL Configuration HOW-TO| 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.
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| 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.
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| 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 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.
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| General Tips on Running SSL |
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 specfied 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.
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| Configuration |
| Prepare the Certificate Keystore |
Tomcat currently operates only on JKS, PKCS11 or
PKCS12 format keystores. The JKS format
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.
The PKCS12 format is an internet standard, and can be manipulated
via (among other things) OpenSSL and Microsoft's Key-Manager.
Each entry in a keystore is identified by an alias string. Whilst many
keystore implementations treat aliases in a case insensitive manner, case
sensitive implementations are available. The PKCS11 specification,
for example, requires that aliases are case sensitive. To avoid issues related
to the case sensitivity of aliases, it is not recommended to use aliases that
differ only in case.
To import an existing certificate into a JKS keystore, please read the
documentation (in your JDK documentation package) about keytool.
Note that OpenSSL often adds readable comments before the key, but
keytool does not support that. So if your certificate has
comments before the key data, remove them before importing the certificate with
keytool.
To import an existing certificate signed by your own CA into a PKCS12
keystore using OpenSSL you would execute a command like:
 | | | | openssl pkcs12 -export -in mycert.crt -inkey mykey.key
-out mycert.p12 -name tomcat -CAfile myCA.crt
-caname root -chain | | | | |
For more advanced cases, consult the OpenSSL
documentation.
To create a new JKS keystore from scratch, containing a single
self-signed Certificate, execute the following from a terminal command line:
Windows:
| | | | "%JAVA_HOME%\bin\keytool" -genkey -alias tomcat -keyalg RSA | | | | |
Unix:
| | | | $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:
Windows:
| | | | "%JAVA_HOME%\bin\keytool" -genkey -alias tomcat -keyalg RSA
-keystore \path\to\my\keystore | | | | |
Unix:
| | | | $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.
This is a restriction of the Tomcat implementation.
(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.
Note: your private key password and keystore password
should be the same. If they differ, you will get an error along the lines
of java.io.IOException: Cannot recover key, as documented in
Bugzilla issue 38217,
which contains further references for this issue.
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| Edit the Tomcat Configuration File |
Tomcat can use two different implementations of SSL:
- the JSSE implementation provided as part of the Java runtime (since 1.4)
- the APR implementation, which uses the OpenSSL engine by default.
The exact configuration details depend on which implementation is being used.
If you configured Connector by specifying generic
protocol="HTTP/1.1" then the implementation used by Tomcat is
chosen automatically. If the installation uses APR
- i.e. you have installed the Tomcat native library -
then it will use the APR SSL implementation, otherwise it will use the Java
JSSE implementation.
As configuration attributes for SSL support significally differ between
APR vs. JSSE implementations, it is recommended to
avoid auto-selection of implementation. It is done by specifying a classname
in the protocol attribute of the Connector.
To define a Java (JSSE) connector, regardless of whether the APR library is
loaded or not, use one of the following:
| | | | <!-- Define a HTTP/1.1 Connector on port 8443, JSSE BIO implementation -->
<Connector protocol="org.apache.coyote.http11.Http11Protocol"
port="8443" .../>
<!-- Define a HTTP/1.1 Connector on port 8443, JSSE NIO implementation -->
<Connector protocol="org.apache.coyote.http11.Http11NioProtocol"
port="8443" .../> | | | | |
Alternatively, to specify an APR connector (the APR library must be available) use:
| | | | <!-- Define a HTTP/1.1 Connector on port 8443, APR implementation -->
<Connector protocol="org.apache.coyote.http11.Http11AprProtocol"
port="8443" .../> | | | | |
If you are using APR, you have the option of configuring an alternative engine to OpenSSL.
| | | |
<Listener className="org.apache.catalina.core.AprLifecycleListener"
SSLEngine="someengine" SSLRandomSeed="somedevice" />
| | | | |
| | | |
<Listener className="org.apache.catalina.core.AprLifecycleListener"
SSLEngine="on" SSLRandomSeed="builtin" />
| | | | |
off.
The default value is on and if you specify another value, it has to be a valid engine name.
SSLRandomSeed allows to specify a source of entropy. Productive system needs a reliable source of entropy
but entropy may need a lot of time to be collected therefore test systems could use no blocking entropy
sources like "/dev/urandom" that will allow quicker starts of Tomcat.
The final step is to configure the Connector in the
$CATALINA_BASE/conf/server.xml file, where
$CATALINA_BASE represents the base directory for the
Tomcat 6 instance. An example <Connector> element
for an SSL connector is included in the default server.xml
file installed with Tomcat. For JSSE, it should look something like this:
| | | |
<!-- Define a SSL Coyote HTTP/1.1 Connector on port 8443 -->
<Connector
protocol="org.apache.coyote.http11.Http11Protocol"
port="8443" maxThreads="200"
scheme="https" secure="true" SSLEnabled="true"
keystoreFile="${user.home}/.keystore" keystorePass="changeit"
clientAuth="false" sslProtocol="TLS"/>
| | | | |
The APR connector uses different attributes for many SSL settings,
particularly keys and certificates. An example of an APR configuration is:
| | | |
<!-- Define a SSL Coyote HTTP/1.1 Connector on port 8443 -->
<Connector
protocol="org.apache.coyote.http11.Http11AprProtocol"
port="8443" maxThreads="200"
scheme="https" secure="true" SSLEnabled="true"
SSLCertificateFile="/usr/local/ssl/server.crt"
SSLCertificateKeyFile="/usr/local/ssl/server.pem"
SSLVerifyClient="optional" SSLProtocol="TLSv1+TLSv1.1+TLSv1.2"/>
| | | | |
The configuration options and information on which attributes
are mandatory for the JSSE based connectors (BIO and NIO) are documented in the
SSL Support section of the HTTP
connector configuration reference. The configuration options and information
on which attributes are mandatory for the APR connector are documented in the
HTTPS section of the APR How-To.
The port attribute 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 Specification.
After completing these configuration changes, you must 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:
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.
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|
| Troubleshooting |
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!
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.
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| Miscellaneous Tips and Bits |
To access the SSL session ID from the request, use:
String sslID = (String)request.getAttribute("javax.servlet.request.ssl_session");
For additional discussion on this area, please see
Bugzilla.
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