In this post we’ll look at how to create our own Certificate Authority (CA) using OpenSSL.
- Generating a Private Key
- Generating a Certificate
- Using the CA
Generating a Private Key
The first step is to create a Private key for our certificate. We can choose either an RSA key or an Elliptic Curve key.
The following command will display a list of supported OpenSSL elliptic curves. We’ll need to choose one of these curves when we are generating our Private key.
1 openssl ecparam -list_curves
1 openssl ecparam -genkey -name secp384r1 -out ca.key
secp384r1is the name of the curve we are using.
ca.keyis the name of the output file where we want to store the Private key.
The following command will generate a 2048-bit RSA key:
1 openssl genrsa -out ca.key
2048-bits is the standard size. A custom key size can be specified by giving an extra argument. The following command will generate a 4096-bit RSA key:
1 openssl genrsa -out ca.key 4096
Generating a Certificate
We need to specify some parameters for our CA before we can create it.
Create a file called
ca.conf and add the following:
1 2 3 4 5 6 7 8 9 10 basicConstraints = CA:TRUE keyUsage = cRLSign, keyCertSign [req] distinguished_name = req_distinguished_name prompt = no [req_distinguished_name] C = AU ST = Victoria L = Melbourne CN = My Personal Root CA
- Customize the
CNto your desired values.
CN (Common Name) field will be displayed when your computer shows the certificate path:
We are now ready to create the certificate using the private key and config:
1 openssl req -x509 -new -sha512 -nodes -key ca.key -days 7307 -out ca.crt -config ca.conf
-x509output a Certificate instead of a Certificate Signing Request (CSR).
-sha512specifies the hash function that will be used to sign the certificate. Other values may be used here such as
-nodesmeans the certificate should be unencrypted.
-key ca.keyspecifies the Private Key we are signing this with.
-days 7307specifies the number of days the certificate is valid for. 7307 days ≈ 20 years.
-out ca.crtspecifies the output file name.
-config ca.confspecifies the configuration file we wish to use.
Using the CA
Now that we have our own Certificate Authority, we can use it sign certificates for web-servers so they can use TLS. I have a guide to do this here.
If we want to use the CA and not have certificate warnings, then it will have to be installed as a Trusted Root CA on your computer/browser.