The mod_ssl_self_signed module adds a basic certificate handling functionality to your Zotonic sites. When this module is enabled and there are no certificates or keys available it generates new keys and self signed certificates to get started easily.

SSL Certificates

For a HTTPS connection special encryption keys and certificates are needed. These are supplied by many companies, for very different price ranges, usage and security levels.

There is an exception, when only a secure connection is needed and the only security is against eaves dropping. This is by using a self signed certificate. This is a key and certificate that is generated on the server, and does not guarantee anything about the validity of the certificate.

When there is no certificate mod_ssl will generate a self signed certificate.

Certificate and key files

The files with the certificates and key are placed into the ssl directory inside the site directory user/sites/sitename/ssl/.

Where sitename must be replaced with the name of your site.

The files all have the name of the site in them (sitename in the filenames below). This is to prevent mixing them up with other sites:

sitename.pem
This holds the private key for the encryption. The key must be unlocked and in PKCS#1 format (see below).
sitename.crt
This is the certificate. Usually it is supplied by the certificate authority where you bought it. It can also be a self signed certificate, see below.
sitename.ca.crt

This is the CA bundle that contains root and intermediate certificates for the certificate authority that issued the sitename.crt certificate.

The certificate authority will supply these. All supplied certificates are concatenated, with the root certificate last.

The concatenation is a literal command, like:

cat intermediate.crt root.crt > sitename.ca.crt

This file should not be present when using a self signed certificate.

Dependencies

When mod_ssl needs to generate or convert key and/or certificates it needs openssl. This program must be installed in the normal search path of the running Zotonic.

Format of the private key

The Erlang SSL implementation uses PKCS#1 format keys. OpenSSL generates (since 2010) PKCS#8 format keys. The difference can be seen when inspecting the key file. A PKCS#1 key starts with:

-----BEGIN RSA PRIVATE KEY-----

Where a PKCS#8 key starts with:

-----BEGIN PRIVATE KEY-----

When mod_ssl sees that the key file is a PKCS#8 file then it will stop and give the following error:

{error, {need_rsa_private_key, "example.pem", "use: openssl rsa -in sitename.key -out sitename.pem"}}

The given command is the command needed to convert the key to a PKCS#1 key. The PKCS#8 key should be renamed to sitename.key from sitename.pem, before running the above command.

Note that the resulting key file must be named sitename.pem where sitename is the name of the site the key is placed in.

Using SSL certificates

If you order a SSL certificate, the signing authority will ask you which kind of web server you are using and a CSR file. For the web server, select other. For the CSR, use the following command (replace sitename with the name of your site):

openssl req -out sitename.csr -new -newkey rsa:2048 -nodes -keyout sitename.key

When OpenSSL asks for the Common Name then fill in the site’s hostname (e.g. www.example.com).

The resulting .key file can be converted to a .pem file:

openssl rsa -in sitename.key -out sitename.pem

From the SSL certificate authority you will receive a signed .crt file.

See the section Certificate and key files above for instructions how to use the .crt and .pem files.

Generating the self signed certificate

For generating the self signed certificate, mod_ssl runs the following commmands (where sitename should be replaced with the name of the site):

openssl req -x509 -nodes -days 3650 -subj '/CN=www.example.com' -newkey rsa:2048 \
     -keyout sitename.key -out sitename.crt

This generates a private key of 2048 bits and a certificate that is valid for 10 years.

Optionally, when the key turns out to be in PKCS#8 format, mod_ssl will run the following command as well:

openssl rsa -in sitename.key -out sitename.pem

When the key is already in PKCS#1 format (with older openssl installs) then mod_ssl will rename the sitename.key file to sitename.pem.

Todo

Add SSL/certificate problem solving.