zulip/docs/production/ssl-certificates.md

SSL Certificates

To keep your communications secure, Zulip runs over HTTPS only. You'll need an SSL/TLS certificate. Fortunately, as of 2017 new options can make getting and maintaining a genuine, trusted-by-browsers certificate no longer the chore (nor expense) that it used to be.

Using Certbot / Let's Encrypt

Let's Encrypt is a free, completely automated CA launched in 2016 to help make HTTPS routine for the entire Web. Zulip offers a simple automation for Certbot, a Let's Encrypt client, to get SSL certificates from Let's Encrypt and renew them automatically.

We recommend most Zulip servers use Certbot. You'll want something else if:

• you have an existing workflow for managing SSL certificates that you prefer;
• you need wildcard certificates (support from Let's Encrypt planned for January 2018); or
• your Zulip server is not on the public Internet. (In this case you can still use Certbot, but it's less convenient; and you'll want to ignore Zulip's automation.)

At initial Zulip install

To enable the Certbot automation when first installing Zulip, just pass the --certbot flag when running the install script.

The --hostname and --email options are required when using --certbot. You'll need the hostname to be a real DNS name, and the Zulip server machine to be reachable by that name from the public Internet.

After Zulip is already installed

To enable the Certbot automation on an already-installed Zulip server, run the following commands:

sudo -s  # If not already root
/home/zulip/deployments/current/scripts/setup/setup-certbot --hostname=HOSTNAME --email=EMAIL

where HOSTNAME is the domain name users see in their browser when using the server (e.g., zulip.example.com), and EMAIL is a contact address for the server admins.

How it works

When the Certbot automation in Zulip is first enabled, by either method, it creates an account for the server at the Let's Encrypt CA; requests a certificate for the given hostname; proves to the CA that the server controls the website at that hostname; and is then given a certificate. (For details, refer to Let's Encrypt.)

Then it records a flag in /etc/zulip/zulip.conf saying Certbot is in use and should be auto-renewed. A cron job checks that flag, then checks if any certificates are due for renewal, and if they are (so approximately once every 60 days), repeats the process of request, prove, get a fresh certificate.

Generating a self-signed certificate

If you aren't able to use Let's Encrypt, you can generate a self-signed ssl certificate. We recommend getting a real certificate using Let's Encrypt over this approach because browsers (and the the Zulip apps) will complain when connecting to your server that the certificate isn't signed (for good reason: self-signed certificates are a security risk!).

Run all the commands in this section as root. If you're not already logged in as root, use sudo -i to start an interactive root shell.

The quickest way to create a cert is to use the script we provide:

scripts/setup/generate-self-signed-certs zulip.example.com

from the root of your Zulip directory (replacing zulip.example.com with the hostname of your server i.e. whatever you're going to set as EXTERNAL_HOST).

Generating a self-signed cert manually

We also document the steps below if you want to create a cert manually, which will offer you an opportunity to set your organization name (etc.).

apt-get install openssl
openssl genrsa -des3 -passout pass:x -out server.pass.key 4096
openssl rsa -passin pass:x -in server.pass.key -out zulip.key
rm server.pass.key
openssl req -new -key zulip.key -out server.csr

# The last step above will ask some questions interactively.
# Run these after answering the questions about your cert.
openssl x509 -req -days 365 -in server.csr -signkey zulip.key -out zulip.combined-chain.crt
rm server.csr
cp zulip.key /etc/ssl/private/zulip.key
cp zulip.combined-chain.crt /etc/ssl/certs/zulip.combined-chain.crt

You will eventually want to get a properly signed SSL certificate, but this will let you finish the installation process.

If you are using a self-signed certificate with an IP address (no domain)

Finally, if you want to proceed with just an IP address, it is possible to finish a Zulip installation that way; just set EXTERNAL_HOST to be the IP address.