Openfire: TLS Guide

# TLS Guide

## Introduction

This document outlines how to manually customize the SSL support in Openfire. As of Openfire 3.2 certificate management can be performed from the Admin Console. However, if needed you can still manually manage certificates using Java Development Kit (JDK) tools.

Important note: Once the setup process is completed Openfire will create self-signed certificates for the assigned Openfire's domain. Most users should either get the created certificates signed by a Certificate Authority or replace the created certificates with your own certificates.

Openfire's SSL support is built using the standard Java security SSL implementation (javax.net.ssl.SSLServerSocket). In this document, we will describe how use the standard Java Development Kit (JDK) tools to accomplish these tasks.

Topics that are covered in this document:

## Background

A server SSL connection uses two sets of certificates to secure the connection. The first set is called a "keystore". The keystore contains the keys and certificates for the server. These security credentials are used to prove to clients that the server is legitimately operating on behalf of a particular domain. If your server will only need to act as one domain, you only need one key entry and certificate in the keystore. Keys are stored in the keystore under aliases. Each alias corresponds to a domain name (e.g. "example.com").

The second set of certificates is called the "truststore" and is used to verify that a client is legitimately operating on behalf of a particular user. In the vast majority of cases, the truststore is empty and the server will not attempt to validate client connections using SSL. Instead, the XMPP authentication process verifies users in-band. However, you may wish to require SSL authentication for certain clients when security is especially important and the number of clients connection to the server is relatively small.

Certificates attempt to guarantee that a particular party is who they claim to be. Certificates are trusted based on who signed the certificate. If you only require light security, are deploying for internal use on trusted networks, etc. you can use "self-signed" certificates. Self-signed certificates encrypts the communication channel between client and server. However, the client must verify the legitimacy of the self-signed certificate through some other channel. The most common client reaction to a self-signed certificate is to ask the user whether to trust the certificate, or to silently trust the certificate is legitimate. Unfortunately, blindly accepting self-signed certificates opens up the system to 'man-in-the-middle' attacks.

The advantage of a self-signed certificate is you can create them for free which is great when cost is a major concern, or for testing and evaluation. In addition, you can safely use a self-signed certificate if you can verify that the certificate you're using is legitimate. So if a system administrator creates a self-signed certificate, then personally installs it on a client's truststore (so that the certificate is trusted) you can be assured that the SSL connection will only work between the client and the correct server.

For higher security deployments, you should get your certificate signed by a certificate authority (CA). Clients truststores will usually contain the certificates of the major CA's and can verify that a CA has signed a certificate. This chain of trust allows clients to trust certificate from servers they've never interacted with before. Certificate signing is similar to a public notary (with equivalent amounts of verification of identity, record keeping, and costs).

## What Domains Need To Be On the Certificate?

Openfire uses two kinds of 'domain names':

- The domain names used in (TCP) networking. Openfire uses the term Fully Qualified Domain Name for this value. This mostly is the hostname of the server that is running Openfire, which is a value that is used in DNS records. This is also typically an address used by HTTP clients (e.g. to access the admin console, but also the websocket endpoint).
- The XMPP domain name of Openfire. This is the value that identifies your domain. It's the part that "comes after the @" in a JID: `userA@mychatservice.im`. It also is used for identifying services on the XMPP domain, which take the form of subdomains of the XMPP domain (e.g. `conference.mychatservice.im`).

The FQDN and XMPP domain name can be configured to be different values (e.g. a server with hostname `xmpp-openfire-1.myhosting.net` can be used to host an XMPP domain name `mychatservice.im`). When FQDN and XMPP domain names are different, they are mapped to each other through DNS SRV records. This is documented in the Openfire: Network Configuration Guide.

A TLS certificate that is used in Openfire needs to be valid for quite a wide range of names:

- The FQDN of the server used by Openfire (otherwise, browsers will raise security alerts when connecting to the admin console, the websocket endpoint, etc.)
- The XMPP domain name served by Openfire (otherwise, non-webbased XMPP clients will typically raise security alerts when connecting, as does server federation, among others).
- Various 'subdomains' of the XMPP domain name (this is a dynamic list, depending on the services that are configured in openfire, but typically includes `conference.mychatserver.im`, `pubsub.mychatserver.im` and `search.mychatserver.org`. These are typically needed only when server federation needs to expose those services.

As you can see, things get convoluted easily. A pragmatic approach to naming things typically is:

- Use the same 'root' domain name for both the FQDN as the XMPP domain name (e.g. `example.org`).
- Use a wildcard certificate that is valid for `example.org` and `*.example.org` both.

If that's not possible, then the certificate needs to be configured for all the domain names, typically using a number of Subject Alternate Name entries in the certificate.

## Oracle Java Development Kit security tools

The Oracle JDK ships with all the security tools you need to configure SSL with Openfire. The most important is the `keytool` located in the `JAVA_HOME/bin directory` of the JDK. Java Virtual Machines persist keystores and truststores on the filesystem as encrypted files. The `keytool` is used to create, read, update, and delete entries in these files. Openfire ships with a self-signed "dummy" certificate designed for initial evaluation testing. You will need to adjust the default configuration for most deployments.

In order to configure SSL on your server you need complete the following tasks:

1. Decide on your Openfire server's domain.
2. Create a self-signed SSL server certificate for your server domain. Note: you may already have one if your Openfire server domain matches an existing web domain with SSL. If so, you can skip to step 4.
3. [Optional] Have a certificate authority (CA) certify the SSL server certificate.
   1. Generate a certificate signing request (CSR).
   2. Submit your CSR to a CA for signing.
4. Import the server certificate into the keystore. Note: if you are going to use a self-signed certificate generated in step 2, the certificate is already imported, and you can skip this step.
5. Remove default certificates from the keystore.
6. Import client certificates into the truststore.
7. Adjust the Openfire configuration with proper keystore and truststore settings.

### 1. Decide on a Server Domain

The Openfire server domain should match the host name of the server; for example, "example.com". Your user accounts will have addresses with the format "user@example.com" like email addresses. We'll assume the domain is "example.com" for the rest of the examples.

### 2. Create a self-signed server certificate

In order to create a self-signed server certificate go to the command line and change directories to the `resources/security` directory of your Openfire installation. You should see the default `keystore` and `truststore` files. First, you should change the default keystore password:

    keytool -storepasswd -keystore keystore

keytool will ask for the old password (by default it is `changeit`) then the new password. Now we'll create a certificate using the keytool:

    keytool -genkey -keystore keystore -alias example.com

where you should substitute your server's name for `example.com`. The keytool will ask for the store password, then several pieces of information required for the certificate. Enter all the information but remember to complete with your server's name when asked for your first and last name. After you have entered all the required information, keytool will ask you to verify the information and set a key password. You must use the same key password as the store password. By default, you get this by simply hitting 'enter' when prompted for a key password.

If you later change the keystore password remember to change the entries' password as well using the keytool:

    keytool -keypasswd -alias example.com -keystore keystore

Keytool will create certificates using the DSA algorithm by default. Some clients expect the server to have RSA certificates or they will fail to use TLS. Therefore, it is a good idea to also create RSA certificates in your keystore. To create certificates with the RSA algorithm you need to specify the algorithm to use like this:

    keytool -genkey -keystore keystore -alias example.com -keyalg RSA

### 3. Obtain a CA signed certificate

If you decide to get a CA signed certificate, you must first export the certificate in the standard CSR format. You can do this with the keytool:

    keytool -certreq -keystore keystore -alias example.com -file certificate_file

Where you should substitute your server's name for `example.com` and the name of the certificate file you wish to produce for `certificate_file`. Submit the generated CSR to the CA and follow their instructions to get it signed.

### 4. Import server certificates

If you had a CA sign your server certificate, or if you have an existing SSL certificate, you must import it using the keytool.

    keytool -import -keystore keystore -alias example.com -file signed_certificate_file

It is important that the alias not already have an associated key or you'll receive an error.

### 5. Remove default certificates

After importing your certificate you must remove the default certificates using the keytool.

    keytool -delete -keystore keystore -alias rsa

    keytool -delete -keystore keystore -alias dsa

### 6. Import client certificates

If you require clients to verify themselves using certificates, obtain their certificates and import them into the truststore file rather than the keystore. First, you should change the default truststore password:

    keytool -storepasswd -keystore truststore

keytool will ask for the old password (by default it is `changeit`) then the new password. Now import each certificate using the keytool:

    keytool -import -keystore truststore -alias user_name -file certificate_file

### 7. Configure Openfire

Open the Openfire Admin Console in your favorite browser and add or change the following system properties:

xmpp.socket.ssl.active
  set to 'true' to active SSL
xmpp.socket.ssl.port
  the port to use for SSL (default is 5223 for XMPP)
xmpp.socket.ssl.storeType
  the store type used ("JKS" is the Sun Java Keystore format used by the JDK keytool). If this property is not defined, Openfire will assume a value of "jks".
xmpp.socket.ssl.keystore
  the location of the keystore file relative to your Openfire installation root directory. You can leave this property blank to use the default keystore.
xmpp.socket.ssl.keypass
  the keystore/key password you changed in step 2.
xmpp.socket.ssl.truststore
  leave blank to not use a truststore, otherwise the location of the truststore file relative to your Openfire installation root directory.
xmpp.socket.ssl.trustpass
  the truststore/key password you changed in step 6.

You will need to restart the server after you have modified any of the above system properties.

## Certificate Revocation

This section covers the configuration of certificate revocation checking in Openfire, including OCSP (Online Certificate Status Protocol) and CRL (Certificate Revocation List) mechanisms. This applies to both roles that Openfire can assume in TLS connections:

1. As a server when:
   - Accepting client connections (C2S)
   - Accepting incoming server-to-server (S2S) connections
2. As a client when:
   - Initiating outbound server-to-server (S2S) connections

### Overview of Revocation Checking Methods

Openfire supports three methods for checking certificate revocation status:

1. OCSP Stapling: The server attaches ("staples") the OCSP response to its certificate during the TLS handshake.
   - Most efficient method
   - Reduces load on OCSP responders
   - Supported in both client and server roles
2. Client-driven OCSP: Direct OCSP responder queries to verify certificate status.
   - Real-time verification
   - Higher network overhead
   - Increased latency during TLS handshake
3. Certificate Revocation Lists (CRL): Downloadable lists of revoked certificates.
   - Periodic updates
   - Can be cached locally
   - Larger bandwidth requirements
   - Can be used as a fallback method

### Configuring Revocation Checking

To enable certificate revocation checking:

1. Go to the Openfire admin console.
2. Navigate to "Server / Server Settings / Server to Server" or "Server / Server Settings / Client Connections".
3. In the "Certificate chain checking" section, locate the option labelled "Verify that certificates have not been revoked (by checking Certificate Revocation Lists and OCSP)".
4. Enable the option to verify certificates against Certificate Revocation Lists (CRL) and through Online Certificate Status Protocol (OCSP).

When this option is enabled, Openfire will check the revocation status of certificates used in server-to-server (S2S) and client-to-server (C2S) connections to ensure they have not been revoked.

#### Fallback behavior when Openfire is the Client (S2S Connections)

When revocation checking is enabled, Openfire employs a multistep process to verify certificate validity using both OCSP and CRLs. When Openfire acts as a client during the TLS handshake and receives certificates from a server, it performs the following revocation checking process:

1. Check OCSP stapled response (if available)
2. Attempt client-driven OCSP query if no stapled response is present
3. Check CRL (if OCSP is unavailable, and CRL is available)
4. Allow the connection to succeed if the revocation status cannot be determined

The system property `xmpp.socket.ssl.certificate.revocation.soft-fail` controls the behavior when revocation status cannot be determined. The default value of this property is `false` which fails the connection if the revocation status of a certificate cannot be determined. If you want to relax revocation checking, you can set this property to `true`. When set to `true`, the connection will be allowed if a certificate's revocation status cannot be established.

By default, revocation checking considers the entire certificate chain. If you want to limit revocation checking to only the leaf certificate in a chain you can set the system property `xmpp.socket.ssl.certificate.revocation.only-end-entity` to `true`.

#### OCSP Stapling

Openfire, when operating as a TLS server and presenting its own certificate, will attempt to staple OCSP responses when both of these conditions are met:

- The certificate includes an OCSP responder URL in its Authority Info Access (AIA) extension.
- The specified OCSP responder returns a valid (non-error) response.

If an OCSP response cannot be obtained, Openfire will present the certificate without an OCSP staple. OCSP stapling improves performance by eliminating the need for clients to make separate requests to verify certificate revocation status.

OCSP stapling is enabled by default. If you need to disable it for any reason, you can set the Java system property `jdk.tls.server.enableStatusRequestExtension` to `false`.

The following configuration options allow you to customise OCSP stapling behavior:

Property | Description | Openfire Default Value
--- | --- | ---
`jdk.tls.server.enableStatusRequestExtension` | Enables the server-side support for OCSP stapling. | True
`jdk.tls.stapling.responseTimeout` | Controls the maximum amount of time the server will use to obtain OCSP responses, whether from the cache or by contacting an OCSP responder. The responses that are already received will be sent in a `CertificateStatus` message, if applicable based on the type of stapling being done. | 5000 (integer value in milliseconds)
`jdk.tls.stapling.cacheSize` | Controls the maximum cache size in entries. If the cache is full and a new response needs to be cached, then the least recently used cache entry will be replaced with the new one. A value of zero or less for this property means that the cache will have no upper bound on the number of responses it can contain. | 256 objects
`jdk.tls.stapling.cacheLifetime` | Controls the maximum life of a cached response. It is possible for responses to have shorter lifetimes than the value set with this property if the response has a nextUpdate field that expires sooner than the cache lifetime. A value of zero or less for this property disables the cache lifetime. If an object has no nextUpdate value and cache lifetimes are disabled, then the response will not be cached. | 3600 seconds (1 hour)
`jdk.tls.stapling.responderURI` | Enables the administrator to set a default URI in the event that certificates used for TLS do not have the Authority Info Access (AIA) extension. It will not override the Authority Info Access extension value unless the `jdk.tls.stapling.responderOverride` property is set. | Not set
`jdk.tls.stapling.responderOverride` | Enables a URI provided through the `jdk.tls.stapling.responderURI` property to override any AIA extension value. | False
`jdk.tls.stapling.ignoreExtensions` | Disables the forwarding of OCSP extensions specified in the `status_request` or `status_request_v2` TLS extensions. | False

## Other options

You can also use OpenSSL to create new private keys and generate certificate requests for your CA to issue new certificates. Also, check out the new Certificate Manager plugin, which allows to set up a hotdeploy directory for new certificates deployment, which in turn combined with Let's Encrypt certbot allows dynamic certificates renewal without administrator intervention.