## SSL/TLS Configuration HOW-TO

### Quick Start

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. ### Introduction to SSL/TLS 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. ### SSL/TLS 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. 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. ### 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. ### 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 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. ### 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). The keytool prompt will tell you that pressing the ENTER key automatically uses the same password for the key as the keystore. You are free to use the same password or to select a custom one. If you select a different password to the keystore password, you will also need to specify the custom password in the server.xml configuration file. 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 Tomcat can use three different implementations of SSL: • JSSE implementation provided as part of the Java runtime • JSSE implementation that uses OpenSSL • 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 JSSE OpenSSL implementation, otherwise it will use the Java JSSE implementation. Auto-selection of implementation can be avoided if needed. 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 NIO implementation --> <Connector protocol="org.apache.coyote.http11.Http11NioProtocol" sslImplementationName="org.apache.tomcat.util.net.jsse.JSSEImplementation" port="8443" .../> <!-- Define a HTTP/1.1 Connector on port 8443, JSSE NIO2 implementation --> <Connector protocol="org.apache.coyote.http11.Http11Nio2Protocol" sslImplementationName="org.apache.tomcat.util.net.jsse.JSSEImplementation" port="8443" .../> The OpenSSL JSSE implementation can also be configured explicitly if needed. If the APR library is installed (as for using the APR connector), using the sslImplementationName attribute allows enabling it. When using the OpenSSL JSSE implementation, the configuration can use either the JSSE attributes or the OpenSSL attributes (as used for the APR connector), but must not mix attributes from both types in the same SSLHostConfig or Connector element. <!-- Define a HTTP/1.1 Connector on port 8443, JSSE NIO implementation and OpenSSL --> <Connector protocol="org.apache.coyote.http11.Http11NioProtocol" port="8443" sslImplementationName="org.apache.tomcat.util.net.openssl.OpenSSLImplementation" .../> 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 or JSSE OpenSSL, you have the option of configuring an alternative engine to OpenSSL. <Listener className="org.apache.catalina.core.AprLifecycleListener" SSLEngine="someengine" SSLRandomSeed="somedevice" /> The default value is <Listener className="org.apache.catalina.core.AprLifecycleListener" SSLEngine="on" SSLRandomSeed="builtin" /> Also the useAprConnector attribute may be used to have Tomcat default to using the APR connector rather than the NIO connector: <Listener className="org.apache.catalina.core.AprLifecycleListener" useAprConnector="true" SSLEngine="on" SSLRandomSeed="builtin" /> So to enable OpenSSL, make sure the SSLEngine attribute is set to something other than off. The default value is on and if you specify another value, it has to be a valid OpenSSL 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 $CATALINA_BASE represents the base directory for the Tomcat instance. An example <Connector> element for an SSL connector is included in the default server.xml file installed with Tomcat. To configure an SSL connector that uses JSSE, you will need to remove the comments and edit it so it looks something like this: <!-- Define a SSL Coyote HTTP/1.1 Connector on port 8443 --> <Connector protocol="org.apache.coyote.http11.Http11NioProtocol" port="8443" maxThreads="200" scheme="https" secure="true" SSLEnabled="true" keystoreFile="${user.home}/.keystore" keystorePass="changeit"
clientAuth="false" sslProtocol="TLS"/>

Note: If tomcat-native is installed, the configuration will use JSSE with an OpenSSL implementation, which supports either this configuration or the APR configuration example given below.

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"
SSLVerifyClient="optional" SSLProtocol="TLSv1+TLSv1.1+TLSv1.2"/>
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