In this blog post I wanted to show how one can use C# or Python to view the serial numbers of a X509 certificate. The serial number can be used to identify the certificate that one plans to use in their C# application, lets say for mutual authentication to another service.

Why use X509 Certificates

  1. Client X.509 certificate identity adds an additional level of asymmetrical cryptography to the standard SSL/TLS channel.
  2. Long security keys (2046 bits)
  3. One can revoke certificates by using Certificate Revocation List (CRL).
  4. Easy to use in application to application
Mutual Authentication

Mutual Authentication

View X509 Certificate Serial Number using C#

If you are using dotnetcore first create a console app using the command below

The command above will create a console app called certsharp and then you can use vscode to load the application.
Below is the sample code that allows one to see the serial number in C#, dotnetcore.

One can the simply run the command below to view the serial, and example show below.

Now lets say you need the serial to find the cert to communicate with another service you can use the code below to find the cert by serial number, and create a rest client to your api like below.

View X509 Certificate Serial Number using Python

For Python I usually create a virtual env before I start coding in python such that I have a separate environment for all my library needs.
To create the virtual env one will need virtualenv installed, you can look at my other Python example of how to install virtualenv and virtualenv-wrapper for windows.

To create a virtual env type the following into your command prompt inside of vscode.

The above command has create the virtual env but not enabled it yet, in order to enable we need to activate it.

Now we can install the package that we need for getting more certificate information, we will use pip and the package is pyopenssl.

Now we can code it up to view the required X509 certificate serial number.

When you run the script it will output something like this


Above are two examples of getting x509 certificate information specifically serial number, there are additional information that one can view, just check out the api documentation.
One additional thing I found is in python it does not show me the leading 00 of a certificate but C# is able to show that.