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Introduction

Users have a choice to use CA-signed certificates and self-signed certificates:

  • CA-signed certificates are issued by a known and trusted Certificate Authority (CA) that validates the domain owner.
  • Self-signed certificates are created by the user and are not related to a known CA.

There is no difference concerning the type of X.509 certificates, the usage for Server Authentication / Client Authentication, or the encryption of connections.

The article explains how to create self-signed certificates by use of OpenSSL. This utility ships with Linux and most Unix environments and is available for Windows environments. The below examples are focused on Unix.

Creating the Root CA Certificate

The first step includes to create the root-ca.key private key file and the root-ca.crt self-signed certificate file for the Root CA both in PEM format. This step is performed just once.

Create Root CA Certificate
# Generate Root Certificate Authority (CA) Private Key
openssl ecparam -name prime256v1 -genkey -noout -out root-ca.key

# Generate Root CA Certificate
openssl req -new -x509 -sha256 -days 5475 -key root-ca.key -out root-ca.crt

# 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) [XX]:DE
# State or Province Name (full name) []:Berlin
# Locality Name (eg, city) [Default City]:Berlin
# Organization Name (eg, company) [Default Company Ltd]:SOS
# Organizational Unit Name (eg, section) []:JS7
# Common Name (eg, your name or your server's hostname) []:JS7 Deployment CA
# Email Address []:


Explanation:

As a response to the second command the OpenSSL utility prompts for a number of specifications for the Distinguished Name, i.e. the unique name of the Root CA Certificate:

  • Country Name: a 2 letter country code is expected as stated for example with https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2
  • State or Province Name: the name of a state is expected
  • Locality Name:  the name of a city is expected
  • Organization Name: arbitrary input is allowed
  • Organizational Unit Name: arbitrary input is allowed
  • Common Name: an arbitrary name can be chosen as the name of the Root CA
  • Email Address: empty input is allowed

Creating a Server Certificate

For a given server the next steps includes to create a private key and Certificate Signing Request (CSR). The resulting server certificate will be signed. 

This step is performed for each server certificate that should be created.

Run the following commands from a bash shell and replace the value of the server variable with the hostname or FQDN for which the certificate should be created:

Create Server Certificate
# Specify server for which the certificate should be created
server=somehost

# Step 1 - Generate Private Key and Certificate Signing Request
openssl req -new -config openssl-cert.config -extensions 'standard exts' -nodes \
    -days 5475 -newkey rsa:4096 -keyout ${server}.key -out ${server}.csr

# Step 2 - Generate and sign the Server Certificate
openssl x509 -req \
    -in ${server}.csr \
    -CA root-ca.crt \
    -CAkey root-ca.key \
    -CAcreateserial \
    -out ${server}.crt -days 7300 \
    -extfile <(printf 'subjectAltName=DNS:%s\nnsCertType = client, server\nkeyUsage = critical, nonRepudiation, digitalSignature, keyEncipherment\nextendedKeyUsage = serverAuth, clientAuth\n' "${server}")


Explanation:

  • The following files will be created for the given server:
    • <server>.key: the Private Key
    • <server>.csr: the Certificate Signing Request
    • <server>.crt: the Server Certificate
  • For operation with JS7 JOC Cockpit, Controller and Agents users can add
    • the Private Key and Server Certificate to a keystore.
    • the Root CA Certificate to a truststore.
  • For details see JS7 - How to add SSL TLS Certificates to Keystore and Truststore

In order to run the script successfully the following openssl-cert.config file has to be present. To create a Server Certificate the CommonName attribute has to be adjusted.

  • Download: openssl-cert.config
  • Replace the value of the commonName attribute with the hostname of the server for which the certificate should be created.
  • Adjust other attributes in the [ standard_dn ] section to your needs.

OpenSSL configuration file openssl-cert.config
[ req ]
prompt             = no
distinguished_name = standard dn

[ standard dn ]
            commonName = somehost
           countryName = DE
          localityName = Berlin
      organizationName = SOS
organizationalUnitName = JS7
   stateOrProvinceName = Berlin

[ standard exts ]
extendedKeyUsage = serverAuth,clientAuth

Resources

Shell Scripts

As an alternative to running OpenSSL commands in an interactive shell a few scripts are provided that perform this task.

The below scripts assume the following directory layout:

  • <ca>  The directory <ca> is a placeholder. Any directory can be used.
    • create_root_ca.sh
    • create_certificate.sh
    • certs
    • csr
    • private

The sub-directories certs, csr and private will be created from the below scripts should they not exist.

Creating the Root CA Certificate

Download: create_root_ca.sh

The following files will be created:

  • <ca>/certs/root-ca.crt
  • <ca>/private/root-ca.key

This step is performed just once. In case of renewal of the Root CA Certificate any Server Certificates will have to be renewed.

Run .create_root_ca.sh shell script
# Description
# create_root_ca.sh --days=<number-of-days>

# Example
./create_root_ca.sh --days=5475


The shell script is executed with an optional single argument:

  • --days
    • The lifetime of the certificate is specified by the number of days (default: 5475, matching approx. 15 years).
    • Consider that server certificates have to be renewed if the Root CA Certificate expires.

Creating a Server Certificate

Download: create_certificate.sh

The following files will be created with <server> being a placeholder for the hostname for which a certificate should be created.

  • <ca>/certs/<server>.crt
  • <ca>/certs/<server>.csr
  • <ca>/private/<server>.key

This step is performed for each Server Certificate that should be created.

Run .create_certificate.sh shell script
# Description
# create_certificate.sh --dns=<server-hostname>[,<server-hostname>] --days=<number-of-days>

# Example
./create_certificate.sh --dns=apmaccs,apmaccs.sos --days=365


The shell script is executed with two arguments:

  • --dns
    • The DNS hostname of the server that should be assigned the certificate. A server can be assigned more than one DNS hostname, for example the FQDN can extend the hostname. Only DNS hostnames that are added to the certificate can be used later on to establish secure HTTPS connections.
  • --days
    • The lifetime of the certificate is specified by the number of days (default: 5475, matching approx. 15 years).