To establish an encrypted connection, we need an encryption key. We also needs some third party authority which verifies, that encryption key belongs to authorized user.

In another words, to establish connection we have to create encryption key for both server and client, create certificate authority (CA) to sign keys and create certification requests. This is generally done using openssl library tool with the same name – openssl. But create all these things with openssl command requires lot of commands with many parameters. For that reason EasyRSA was created, which simplifies this procedure.

Following steps should be done on some secured system dedicated for storing CA and key signing. It is recommended to keep this computer in locked room and completely disconnected from the network. For purpose of this article, I create all files in my /tmp directory.

First of all download EasyRSA from GitHub:

$ git clone https://github.com/OpenVPN/easy-rsa

Next, change working directory and create configuration file:

$ cd easy-rsa/easyrsa3
easy-rsa/easyrsa3$ cp vars.example vars
easy-rsa/easyrsa3$ nano vars

Now edit configuration values. Most important are following variables:

#set_var EASYRSA_REQ_COUNTRY     "US"
#set_var EASYRSA_REQ_PROVINCE    "California"
#set_var EASYRSA_REQ_CITY        "San Francisco"
#set_var EASYRSA_REQ_ORG "Copyleft Certificate Co"
#set_var EASYRSA_REQ_EMAIL       "me@example.net"
#set_var EASYRSA_REQ_OU          "My Organizational Unit"

Just uncomment them and assign them appropriate literals. If you want to omit some of these values (such as EASYRSA_REQ_OU) fill it with . (dot).

After EasyRSA is configured, you can initialize public key infrastructure (PKI):

easy-rsa/easyrsa3$ ./easyrsa init-pki

After that, empty pki should look like this:

easy-rsa/easyrsa3$ tree pki/
pki/
├── private
└── reqs

First this what have to be created is CA.

easy-rsa/easyrsa3$ ./easyrsa build-ca

Note: using Easy-RSA configuration from: ./vars
Generating a 2048 bit RSA private key
...................................................+++
..+++
writing new private key to '/tmp/easy-rsa/easyrsa3/pki/private/ca.key.EYi53CVs1x'
Enter PEM pass phrase:
Verifying - Enter PEM pass phrase:
-----
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.
-----
Common Name (eg: your user, host, or server name) [Easy-RSA CA]:my-ca

CA creation complete and you may now import and sign cert requests.
Your new CA certificate file for publishing is at:
/tmp/easy-rsa/easyrsa3/pki/ca.crt

Command build-ca creates CA files encrypted with pass phrase. You can append nopass argument to create plaintext CA. I recommend you to protect it. Command also asks for common name. It should be some meaningful string, as the prompt suggests.

Next, create server key and certificate request file:

easy-rsa/easyrsa3$ ./easyrsa gen-req server-cert nopass

Note: using Easy-RSA configuration from: ./vars
Generating a 2048 bit RSA private key
..+++
............+++
writing new private key to '/tmp/easy-rsa/easyrsa3/pki/private/server-cert.key.LlGDzHp1hN'
-----
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.
-----
Common Name (eg: your user, host, or server name) [server-cert]:

Keypair and certificate request completed. Your files are:
req: /tmp/easy-rsa/easyrsa3/pki/reqs/server-cert.req
key: /tmp/easy-rsa/easyrsa3/pki/private/server-cert.key

In this case I recommend you to use nopass argument. Otherwise you will have to manually type a pass phrase every time you want to start a VPN server, which is nonsence.

Command again asks for common name. In case of server key, it must match the server hostname. This is the way how the client verifies that it is authenticating with correct machine. If common name doesn't match to server hostname, certificate verification fails.

Next, sign server request with your CA:

easy-rsa/easyrsa3$ ./easyrsa sign-req server server-cert

Note: using Easy-RSA configuration from: ./vars


You are about to sign the following certificate.
Please check over the details shown below for accuracy. Note that this request
has not been cryptographically verified. Please be sure it came from a trusted
source or that you have verified the request checksum with the sender.

Request subject, to be signed as a server certificate for 3650 days:

subject=
    commonName                = server-cert


Type the word 'yes' to continue, or any other input to abort.
  Confirm request details: yes
Using configuration from /tmp/easy-rsa/easyrsa3/openssl-1.0.cnf
Enter pass phrase for /tmp/easy-rsa/easyrsa3/pki/private/ca.key:
Check that the request matches the signature
Signature ok
The Subject's Distinguished Name is as follows
commonName            :ASN.1 12:'server-cert'
Certificate is to be certified until Apr 30 08:39:15 2026 GMT (3650 days)

Write out database with 1 new entries
Data Base Updated

Certificate created at: /tmp/easy-rsa/easyrsa3/pki/issued/server-cert.crt

If CA is encrypted, command asks for its pass phrase.

Last step is create Diffie-Hellman parameters for initial key exchange:

easy-rsa/easyrsa3$ ./easyrsa gen-dh
 
Note: using Easy-RSA configuration from: ./vars
Generating DH parameters, 2048 bit long safe prime, generator 2
This is going to take a long time
........................... [ … snip … ] ........++*++*
 
DH parameters of size 2048 created at /tmp/easy-rsa/easyrsa3/pki/dh.pem

Generating client side certificates is very similar to generating server side one. Generating certificate request is exactly same:

easy-rsa/easyrsa3$ ./easyrsa gen-req client-cert nopass

Note: using Easy-RSA configuration from: ./vars
Generating a 2048 bit RSA private key
........................+++
..........................................+++
writing new private key to '/tmp/easy-rsa/easyrsa3/pki/private/client-cert.key.VXHcRiIzab'
-----
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.
-----
Common Name (eg: your user, host, or server name) [client-cert]:

Keypair and certificate request completed. Your files are:
req: /tmp/easy-rsa/easyrsa3/pki/reqs/client-cert.req
key: /tmp/easy-rsa/easyrsa3/pki/private/client-cert.key

Sign certificate request of client type by following command:

easy-rsa/easyrsa3$ ./easyrsa sign-req client client-cert

Note: using Easy-RSA configuration from: ./vars


You are about to sign the following certificate.
Please check over the details shown below for accuracy. Note that this request
has not been cryptographically verified. Please be sure it came from a trusted
source or that you have verified the request checksum with the sender.

Request subject, to be signed as a client certificate for 3650 days:

subject=
    commonName                = client-cert


Type the word 'yes' to continue, or any other input to abort.
  Confirm request details: yes
Using configuration from /tmp/easy-rsa/easyrsa3/openssl-1.0.cnf
Enter pass phrase for /tmp/easy-rsa/easyrsa3/pki/private/ca.key:
Check that the request matches the signature
Signature ok
The Subject's Distinguished Name is as follows
commonName            :ASN.1 12:'client-cert'
Certificate is to be certified until Apr 30 08:40:49 2026 GMT (3650 days)

Write out database with 1 new entries
Data Base Updated

Certificate created at: /tmp/easy-rsa/easyrsa3/pki/issued/client-cert.crt