Links User Guide Reference Apache Tomcat Development | | 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 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
Certificate Authority (CA) such as VeriSign or Thawte. Such
certificates can be electronically verified -- in effect, the Certificate
Authority will vouch for the authenticity of the certificates that it grants,
so you can believe that that Certificate is valid if you trust the Certificate
Authority that granted it.
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.
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| 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 if 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.
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| Configuration |
| Prepare the Certificate Keystore |
Tomcat currently operates with 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 implmentations treat alaises 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 aliaises, 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 a readable comments before the key, keytooldoes not support that, so remove the openssl comments if they exist before importing the key using 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
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To create a new keystore from scratch, containing a single self-signed
Certificate, execute the following from a terminal command line:
Windows:
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%JAVA_HOME%\bin\keytool -genkey -alias tomcat -keyalg RSA
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Unix:
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$JAVA_HOME/bin/keytool -genkey -alias tomcat -keyalg RSA
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(The RSA algorithm should be preferred as a secure algorithm, and this
also ensures general compatibility with other servers and components.)
This command will create a new file, in the home directory of the user
under which you run it, named ".keystore". To specify a
different location or filename, add the -keystore parameter,
followed by the complete pathname to your keystore file,
to the keytool command shown above. You will also need to
reflect this new location in the server.xml configuration file,
as described later. For example:
Windows:
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%JAVA_HOME%\bin\keytool -genkey -alias tomcat -keyalg RSA \
-keystore \path\to\my\keystore
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Unix:
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$JAVA_HOME/bin/keytool -genkey -alias tomcat -keyalg RSA \
-keystore /path/to/my/keystore
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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.
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 38217,
which contains further references for this issue.
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| 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 5. 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:
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<-- Define a SSL Coyote HTTP/1.1 Connector on port 8443 -->
<!--
<Connector
port="8443" minProcessors="5" maxProcessors="75"
enableLookups="true" disableUploadTimeout="true"
acceptCount="100" debug="0" scheme="https" secure="true";
clientAuth="false" sslProtocol="TLS"/>
-->
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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 2.4 Specification.
There are addional option used to configure the SSL protocol.
You may need to add or change the following attribute
values, depending on how you configured your keystore earlier:
| Attribute |
Description |
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. Set this value to want if you want Tomcat
to request a client Certificate, but not fail if one isn't presented.
For using clientAuth on a per-user or per-session basis, check out
the tips in
Bugzilla 34643.
|
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). |
keystoreType |
Add this element if using a keystore type other than
JKS. |
sslProtocol |
The encryption/decryption protocol to be used on this socket.
It is not recommended to change this value if you are using Sun's
JVM. It is reported that IBM's 1.4.1 implementation
of the TLS protocol is not compatible with some popular browsers.
In this case, use the value SSL. |
ciphers |
The comma separated list of encryption ciphers that this socket is
allowed to use. By default, the default ciphers for the JVM will be
used. Note that this usually means that the weak export grade ciphers
will be included in the list of available ciphers. The ciphers are
specified using the JSSE cipher naming convention. |
algorithm |
The X509 algorithm to use. This defaults to the Sun
implementation (SunX509). For IBM JVMs you should use
the value IbmX509. For other vendors, consult the JVM
documentation for the correct value.
|
truststoreFile |
The TrustStore file to use to validate client certificates. |
truststorePass |
The password to access the TrustStore. This defaults to the value
of keystorePass. |
truststoreType |
Add this element if your are using a different format for the
TrustStore then you are using for the KeyStore. |
keyAlias |
Add this element if your have more than one key in the KeyStore.
If the element is not present the first key read in the KeyStore
will be used. |
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.
- 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 <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 errorjavax.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 withinthe 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.
For tips on using clientAuth on a per-user or per-session basis, and also for
using clientAuth with self-signed or expired client certificates, please see the
discussion in
Bugzilla 34643.
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