VPS Setup

Root certificate

We’re going to generate SSL certs for various services later on. These will need to be signed by a CA. If you’re feeling particularly rich or for some reason don’t want to go through the hassle of adding your own root cert to a bunch of client machines, go ahead and buy one from a legitimate CA.

Otherwise you can generate a custom CA cert as follows:

openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:4096 -out cakey.pem -des3
chmod 600 cakey.pem
openssl req -x509 -new -nodes -key cakey.key -days 3650 -out cacert.pem
cp cacert.pem /etc/ssl/certs/
cp cakey.pem /etc/ssl/private/

Keep your CA key safe and encrypt it with a strong passphrase

On every client machine (i.e. one from which you will later want to read or write emails) you will need to add cacert.pem to the list of trusted certificates.

On Linux, and most other flavors of UNIX, this is as simple as copying that file to /etc/ssl/certs. Make sure to give it a name that won’t clash with existing certs (your own name is probably a safe choice).

Save the following script as gencert.sh alongside your CA cert. It will be used later on to sign new certificates.



touch $key
chmod 600 $key
openssl genrsa 2048 > $key
openssl req -new -key $key -out $csr
openssl x509 -req -in $csr -CA $cacert -CAkey $cakey -CAcreateserial \
    -out $cert -days 3650
rm $csr

Dont’t forget to make it executable:

chmod +x gencert.sh

NOTE: All the certs generated by the above command are valid for 10 years. You might want to increase or decrease that value depending on what security vs convenience trade-off you’re willing to make.