OpenSSL for X.509 certificates
Recently I’d to generate an X.509 certificate to enable encryption connections to a web app. The browser performs a check to ensure that the connection is via a valid, trusted certificate, later on we’ll be using a 3rd party entity known as a Certificate Authority (CA) to do just that.
We’ll be using
openssl to generate a private key. This key manifests in the form of a file, so we’ll call it a .key file, which we’ll also make read only:
$ openssl genrsa -out privkey.pem Generating RSA private key, 2048 bit long modulus .........................................................+++ .......................+++ $ chmod 400 privkey.key
cat privkey.key, the first and last lines of your .key will be
-----BEGIN RSA PRIVATE KEY----- and
-----END RSA PRIVATE KEY-----.
This key file is the first half of the equation in public key cryptography. For the second half, we need to submit a Certificate Signing Request (CSR) to a 3rd party entity known as a Certificate Authority (CA).
The CSR is generated using
privkey.pem as an inputs. A CSR manifests in the form of a file, which we’ll call a .csr file. Samples for the various other inputs are also provided below:
$ openssl req -new -sha256 -days 825 -key privkey.pem -out signme.csr 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) [SG]:SG State or Province Name (full name) [Singapore]:Singapore Locality Name (eg, city) [Singapore]:Singapore Organization Name (eg, company) [Internet Widgits Pty Ltd]:GitHub Organizational Unit Name (eg, section) : Common Name (e.g. server FQDN or YOUR name) :waynekhan.github.io Email Address :[email protected] Please enter the following 'extra' attributes to be sent with your certificate request A challenge password : An optional company name :
cat signme.csr, the first and last lines will be
-----BEGIN CERTIFICATE REQUEST----- and
-----END CERTIFICATE REQUEST-----.
You must therefore provide this file to your CA in order to generate a public certificate, also in the form of a file. If you
cat this file, the first and last lines will be
-----BEGIN CERTIFICATE----- and
-----END CERTIFICATE-----. You may also see more than one of these; i.e., a certificate chain, so I’ve creatively named this file as
Thereafter, depending on what kind of application you use (e.g.,
nginx), the precise configuration is a bit different, but you’ll always need to use your private key
privkey.pem and public certificate
fullchain.pem in order for HTTPS clients to be able to (i) identify your server; (ii) encrypt the connection.