In my last article I described how to generate your own self-signed SSL certificates and add them to macOS Keychain so that your browser doesn’t give you a privacy error.
Soon after it was published, Ross McKay made a very interesting comment on that article:
If you have a few servers you need to do this with, you can just create yourself a CA (Certifying Authority) certificate and load that instead. Then your self-signed certs, signed by your CA cert, will all be accepted without you needing to load each one.
So basically he’s saying that I can be a certificate authority (CA) like Let’s Encrypt, Amazon, Verisign, Comodo, etc but just for my local network. How did I not know about that? So cool. But how does it work exactly?
How It Works
After some research I think I get it now. To request a certificate from a CA like Verisign, you send them a Certificate Signing Request (CSR), and they give you a certificate in return that they signed using their root certificate and private key. All browsers have a copy (or access a copy from the operating system) of Verisign’s root certificate, so the browser can verify that your certificate was signed by a trusted CA.
That’s why when you generate a self-signed certificate the browser doesn’t trust it. It’s self-signed. It hasn’t been signed by a CA. But as Ross pointed out, we can generate our own root certificate and private key, add the root certificate to all the devices we own just once, and then all certificates that we generate and sign will be inherently trusted.
Becoming a (tiny) Certificate Authority
It’s kind of ridiculous how easy it is to generate the files needed to become a certificate authority. It only takes two commands. First, we generate our private key:
openssl genrsa -des3 -out myCA.key 2048
You will be prompted for a pass phrase, which I recommend not skipping and keeping safe. The pass phrase will prevent anyone who gets your private key from generating a root certificate of their own. Output should look like this:
Generating RSA private key, 2048 bit long modulus
.................................................................+++
.....................................+++
e is 65537 (0x10001)
Enter pass phrase for myCA.key:
Verifying - Enter pass phrase for myCA.key:
Then we generate a root certificate:
openssl req -x509 -new -nodes -key myCA.key -sha256 -days 1825 -out myCA.pem
You will prompted for the pass phrase of your private key (that you just choose) and a bunch of questions. The answers to those questions aren’t that important. They show up when looking at the certificate, which you will almost never do. I suggest making the Common Name something that you’ll recognize as your root certificate in a list of other certificates. That’s really the only thing that matters.
Enter pass phrase for myCA.key:
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [AU]:CA
State or Province Name (full name) [Some-State]:Nova Scotia
Locality Name (eg, city) []:Truro
Organization Name (eg, company) [Internet Widgits Pty Ltd]:Delicious Brains Inc
Organizational Unit Name (eg, section) []:
Common Name (e.g. server FQDN or YOUR name) []:Delicious Brains
Email Address []:noreply@deliciousbrains.com
You should now have two files: myCA.key (your private key) and myCA.pem (your root certificate).
🎉 Congratulations, you’re now a CA. Sort of.
To become a real CA, you need to get your root certificate on all the devices in the world. Let’s start with the ones you own.
Installing Your Root Certificate
We need to add the root certificate to any laptops, desktops, tablets, and phones that will be accessing your HTTPS sites. This can be a bit of a pain, but the good news is that we only have to do it once. Once our root certificate is on each device, it will be good until it expires.
Adding the Root Certificate to macOS Keychain
- Open the macOS Keychain app
- Go to File > Import Items…
- Select your private key file (i.e. myCA.pem)
- Search for whatever you answered as the Common Name name above
- Double click on your root certificate in the list
- Expand the Trust section
- Change the When using this certificate: select box to “Always Trust”
- Close the certificate window
- It will ask you to enter your password (or scan your finger), do that
- 🎉 Celebrate!
Creating CA-Signed Certificates for Your Dev Sites
Now that we’re a CA on all our devices, we can sign certificates for any new dev sites that need HTTPS. First, we create a private key:
openssl genrsa -out dev.mergebot.com.key 2048
Then we create a CSR:
openssl req -new -key dev.mergebot.com.key -out dev.mergebot.com.csr
You’ll get all the same questions as you did above and, again, your answers don’t matter. In fact, they matter even less because you won’t be looking at this certificate in a list next to others.
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [AU]:CA
State or Province Name (full name) [Some-State]:Nova Scotia
Locality Name (eg, city) []:Truro
Organization Name (eg, company) [Internet Widgits Pty Ltd]:Delicious Brains Inc
Organizational Unit Name (eg, section) []:
Common Name (e.g. server FQDN or YOUR name) []:Mergebot
Email Address []:noreply@mergebot.com
Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:
Next we’ll create the certificate using our CSR, the CA private key, the CA certificate, and a config file, but first we need to create that config file.
The config file is needed to define the Subject Alternative Name (SAN) extension we discussed in my last article. I created a new file named dev.mergebot.com.ext and added the following contents:
authorityKeyIdentifier=keyid,issuer
basicConstraints=CA:FALSE
keyUsage = digitalSignature, nonRepudiation, keyEncipherment, dataEncipherment
subjectAltName = @alt_names
[alt_names]
DNS.1 = dev.mergebot.com
DNS.2 = dev.mergebot.com.192.168.1.19.xip.io
We’re using a different config file for the SAN than in my last article because we’ll be running the openssl x509 command instead of the openssl req command. From what I understand, the x509 command is needed to do the signing with the root certificate and private key. Again, I found this example config file on Stack Overflow and it seems to work.
Now we run the command to create the certificate:
openssl x509 -req -in dev.mergebot.com.csr -CA myCA.pem -CAkey myCA.key -CAcreateserial \
-out dev.mergebot.com.crt -days 1825 -sha256 -extfile dev.mergebot.com.ext
You should be prompted for your CA private key pass phrase.
I now have three files: dev.mergebot.com.key (the private key), dev.mergebot.com.csr (the certificate signing request), and dev.mergebot.com.crt (the signed certificate).
I can now configure my web server with the private key and the certificate. If you’re running a Linux server, you can use the instructions in our Hosting WordPress Yourself series. If you’re using MAMP, you can select the certificate and key files using the UI:
For any other dev sites, we can just repeat this last part of creating a certificate. No need to install any new certificates on any of my devices. Much better.
Conclusion
After going through the process of setting up my own CA and signing certificates with it, there’s no question this is a better way to go than creating individual self-signed certificates as described in my last article. The fact that you only have to setup the CA and add it to your devices once means you save a bunch of time for each new certificate you create in the future. It’s a no-brainer to go this route.
Have you tried setting up a CA of your own? Maybe you’ve been using your own CA for years? Are there any drawbacks that I missed? Let me know in the comments below.