How to work with certificates

Description

This section explains how to use openssl commands to validate a chain of certificates (CA, intermediate, and server), and separate or combine certificates.

You can bring certificates as follows:

• Scenario 1: Three crt/pem files including CA, intermediate, and server certs and a private key.

• Scenario 2: Two crt/pem files including CA and server certs and a private key.

• Scenario 3: One pfx file containing all CA/intermediate and server certs and a private key.

The following table describes the used file names:

File name	Description
ca.crt	A CA certificate.
intermediate.crt	An intermediate certificate.
ca-bundle.crt	A certificate containing CA and intermediate certificates.
server.crt	A server certificate.
server.key	A private key used to generate the server.crt.
server.pfx	A pfx certificate file containing CA, intermediate, server certificates, and the server private key.

Scenario 1 and Scenario 2

When you bring three different cert files (CA, intermediate, and server), take the following steps for validation:

1. Combine the CA with the intermediate certs (applicable only for Scenario 1).

   cp ca.crt ca-bundle.crt
   cat intermediate.crt >> ca-bundle.crt

2. Check the server cert contains (specifically the subject alternative names and validity fields.

   openssl x509 -in server.crt -text -noout

3. Check if the server cert was signed by the CA server.

   openssl verify -CAfile ca-bundle.crt server.crt

   Output:

   server.crt: OK

4. Check if the server cert was generated by the server private key by comparing the md5 hashes. If the following commands' outputs match, then it validates that the server cert was generated using the private key.

   • openssl x509 -noout -modulus -in server.crt | openssl md5

     Server cert output:

     (stdin)= c9b0c5c3fe11b0b09947415236c4a441

   • openssl rsa -noout -modulus -in server.key | openssl md5

     Server private key output:

     (stdin)= c9b0c5c3fe11b0b09947415236c4a441

5. Generate the pfx file from the server cert and the private key. Once the following command is run, you are prompted to type a passcode twice. Thepasscode is always required to decrypt the pfx file.

   openssl pkcs12 -inkey server.key -in server.crt -export -out server.pfx

   Output:

   Enter Export Password:
   Verifying - Enter Export Password:

Scenario 3

When you bring one certificate in pfx format containing CA, intermediate, server, and private key, you can use the pfx file as an identity token signing certificate, but you must break the pfx file into multiple cert files. The following steps describe how to break the pfx file accordingly.

1. Export the CA certificate (including intermediate if provided in the pfx file):

   openssl pkcs12 -in server.pfx -cacerts -nokeys -chain | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > ca.crt

2. Export the server certificate:

   openssl pkcs12 -in server.pfx -clcerts -nokeys | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > server.crt

3. Export the private key:

   openssl pkcs12 -in server.pfx -nocerts -nodes | sed -ne '/-BEGIN PRIVATE KEY-/,/-END PRIVATE KEY-/p' > server.key