Self Signed Certificate with Custom Root CA

self-signed-certificate-with-custom-ca.md

Create Root CA (Done once)

Create Root Key

Attention: this is the key used to sign the certificate requests, anyone holding this can sign certificates on your behalf. So keep it in a safe place!

openssl genrsa -des3 -out rootCA.key 4096

If you want a non password protected key just remove the -des3 option

Create and self sign the Root Certificate

openssl req -x509 -new -nodes -key rootCA.key -sha256 -days 1024 -out rootCA.crt

Here we used our root key to create the root certificate that needs to be distributed in all the computers that have to trust us.

Import this into your browser

This only works for browsers you control

I tried importing to my OS certifiocates but that didn't work for me

Importing my rootCA.crtto the browsers did work (eventually)

Create a certificate (Done for each server)

This procedure needs to be followed for each server/appliance that needs a trusted certificate from our CA

My example is for a local dev server where I have a matching entry in my /etc/hosts file for the IP

Create the certificate key

openssl genrsa -out dot.burlington.me.uk.key 2048

Create the signing (csr)

The certificate signing request is where you specify the details for the certificate you want to generate. This request will be processed by the owner of the Root key (you in this case since you create it earlier) to generate the certificate.

Important: Please mind that while creating the signign request is important to specify the Common Name providing the IP address or domain name for the service, otherwise the certificate cannot be verified.

You also need to specify a SAN / subjectAltName or chrome wont accept it

    
openssl req -new -sha256 \
    -key dot.burlington.me.uk.key \
    -subj "/C=UK/ST=Dorset/O=Tangible Bytes Ltd/OU=Development/CN=dot.burlington.me.uk" \
    -reqexts SAN \
    -config <(cat /etc/ssl/openssl.cnf <(printf "\n[SAN]\nsubjectAltName=DNS:dot.burlington.me.uk")) \
    -out dot.burlington.me.uk.csr

    

Verify the csr's content

openssl req -in dot.burlington.me.uk.csr -noout -text

Generate the certificate using the custom csr and key along with the CA Root key

openssl x509 -req -extfile <(printf "subjectAltName=DNS:dot.burlington.me.uk") -days 120 -in dot.burlington.me.uk.csr -CA rootCA.crt -CAkey rootCA.key -CAcreateserial -out dot.burlington.me.uk.crt -sha256

Verify the certificate's content

openssl x509 -in dot.burlington.me.uk.crt -text -noout