Best location to keep SSL certificates and private keys on Ubuntu servers?

The .crt file is sent to everything that connects; it is public. (chown root:root and chmod 644)

To add to the private key location; make sure you secure it properly as well as having it in there. (chown root:ssl-cert and chmod 640)

It really doesn't matter where you put them as long as you properly protect your private key file(s). The public certificate is public; no protection needed - server privileges or otherwise.

To expand on the answer, I do not use the default location /etc/ssl.
It's easier for me to keep all mine in a separate area due to backups+other reasons.

For Apache SSL, I keep mine in /etc/apache2/ssl/private or similar "root area" in /etc/apache2.

Example Setup

This post is geared toward Ubuntu (Debian) + Apache, but should work on most systems.
Just apply the permissions and update location/path in given config (apache/nginx/etc).

This answer also assumes you are NOT using LetsEncrypt/Certbot, or some automated SSL service. You have bought, or created a SSL certificate and have obtained the file bundle.

If the SSL key file(s) are protected correctly (directory & files), you will be fine. Note the notes!

Create directories:

sudo mkdir /etc/apache2/ssl
sudo mkdir /etc/apache2/ssl/private
sudo chmod 755 /etc/apache2/ssl
sudo chmod 710 /etc/apache2/ssl/private

Note:
chmod 710 supports ssl-cert group under Ubuntu. (See comments)
Setting permission to 700 on /etc/apache2/ssl/private will also work fine.

Place SSL files:

Put the public SSL certificate(s) AND intermediate certificate(s) in:
/etc/apache2/ssl (These are *.crt files, normally)

Put the corresponding private SSL key(s) in:
/etc/apache2/ssl/private (These are *.key files, or no extension, normally)

Note: LetsEncrypt/Certbot uses the ".pem" extension for all SSL files (public, intermediate chains and private). But, you do not need to move (or protect) those files. They are already in place and protected. Just call them directly in your Apache '.conf'.

Set owner:

Note - If you do not have a ssl-cert group, just skip the 2nd line:

sudo chown -R root:root /etc/apache2/ssl/
sudo chown -R root:ssl-cert /etc/apache2/ssl/private/

Set permissions:

Public Certificate(s)

sudo chmod 644 /etc/apache2/ssl/*.crt

Private Key(s)

sudo chmod 640 /etc/apache2/ssl/private/*.key

Note:
The group permission for private key(s) is set to READ (640) due to Ubuntu ssl-cert group. Using '600' (owner only control) is the normal permission for private keys and will work fine as well.

Enable the Apache SSL module

sudo a2enmod ssl

Edit any Apache site files and enable

(see last paragraph) *

sudo nano /etc/apache/sites-available/mysiteexample-ssl.conf
sudo a2ensite mysiteexample-ssl
#             ^^^^^^^^^^^^^^^^^ <-Substitute your ".conf" filename(s)

Restart Apache2 service

sudo service apache2 restart

or

sudo systemctl restart apache2.service

Done. Test your new SSL site.

* Again this goes beyond the question, but you can copy the default Apache SSL site configuration file (sudo cp /etc/apache2/sites-available/default-ssl.conf /etc/apache2/sites-available/mysiteexample-ssl.conf) as a good starting point/example of default directives/directories normally used under a simple (Ubuntu/Debian) Apache/SSL 'conf' file. It normally points to a self-signed SSL certificate+key (snakeoil), CA bundles, as well as common directives used for a given SSL site.

After copying, just edit the new .conf file and add/remove/update it as needed with new information/paths above then execute sudo a2ensite mysiteexample-ssl to enable it. Reload/restart apache2. Test.

All the answers here seem OK, but I want to mention one thing I found is a problem... If you have to concatenate your cert with intermediates or roots to come up with a chain file, don't put that in /etc/ssl/certs, because when c_rehash is run, it may create hash symlinks to your certs due to the roots or intermediates within them.

Then later down the road if your certs have expired and you remove them, and don't know to re-run c_rehash, you may have broken hash symlinks in your /etc/ssl/certs directory, and weird things start happening when your local machine tries to connect to itself through SSL, and it can't find the roots to validate against. For example, with curl I suddenly started getting:

curl: (60) SSL certificate problem: unable to get issuer certificate

Shortly after cleaning up some old .crt and concatenated .pem files I had in /etc/ssl/certs.

Storing at least your chains somewhere else avoids this problem. I ended up making a /etc/ssl/local_certs to hold my certs and chains, so they weren't lost in the mess of CA certs you'll find in /etc/ssl/certs

Locations are correct:

• /etc/ssl/certs/ for .crt file
• /etc/ssl/private for .key file

Owner:

• root:root for /etc/ssl/certs
• root:ssl-cert for /etc/ssl/private

Permissions:

• 644 for .crt file
• 600 for .key file

This will work for nginx.

There's not really an unsafe place if permission for the individual files/directory is set to something like chown root :0 private.key and chmod 600 private.key so that only root can read it. CSRs and certificate files are less sensitive as you say.

With those permissions the paths you mention and /usr/local/ssl should be fine.