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 ecparam -genkey -name prime256v1 -noout -out rootCA.key
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.
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
Create the certificate key
openssl ecparam -name prime256v1 -genkey -noout -out mydomain.com.key
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.
Method A (Interactive)
If you generate the csr in this way, openssl will ask you questions about the certificate to generate like the organization details and the
Common Name (CN) that is the web address you are creating the certificate for, e.g
openssl req -new -key mydomain.com.key -out mydomain.com.csr
Method B (One Liner)
This method generates the same output as Method A but it's suitable for use in your automation :) .
openssl req -new -sha256 -key mydomain.com.key -subj "/C=US/ST=CA/O=MyOrg, Inc./CN=mydomain.com" -reqexts SAN -config <(cat /etc/ssl/openssl.cnf <(printf "\n[SAN]\nsubjectAltName=DNS:YOUR_DOMAIN_NAME")) -out mydomain.com.csr
If you need to pass additional config you can use the
-config parameter, here for example I want to add alternative names to my certificate.
openssl req -new -sha256 \ -key mydomain.com.key \ -subj "/C=US/ST=CA/O=MyOrg, Inc./CN=mydomain.com" \ -reqexts SAN \ -config <(cat /etc/ssl/openssl.cnf \ <(printf "\n[SAN]\nsubjectAltName=DNS:mydomain.com,DNS:www.mydomain.com")) \ -out mydomain.com.csr
Verify the csr's content
openssl req -in mydomain.com.csr -noout -text
Generate the certificate using the
mydomain csr and key along with the CA Root key
openssl x509 -req -extfile <(printf "subjectAltName=DNS:YOUR_DOMAIN_NAME") -in mydomain.com.csr -CA rootCA.crt -CAkey rootCA.key -CAcreateserial -out mydomain.com.crt -days 500 -sha256
Verify the certificate's content
openssl x509 -in mydomain.com.crt -text -noout