.NET API Browser

Accessing Certificate Extensions

The following example demonstrates how to retrieve and display the extensions from an X.509 certificate.

using System;
using System.Security.Cryptography.X509Certificates;
using System.Text;

public class CertificateExtensionsExample
{
    public static void Main(string[] args)
    {
        try
        {
            // Load a sample X.509 certificate (replace with your actual certificate loading logic)
            // For demonstration, we'll try to load a local machine certificate.
            X509Certificate2 cert = null;
            X509Store store = new X509Store(StoreName.My, StoreLocation.CurrentUser);
            store.Open(OpenFlags.ReadOnly);
            if (store.Certificates.Count > 0)
            {
                cert = store.Certificates[0]; // Select the first certificate
            }
            store.Close();

            if (cert != null)
            {
                Console.WriteLine($"Certificate Subject: {cert.Subject}");
                Console.WriteLine("--- Extensions ---");

                if (cert.Extensions.Count == 0)
                {
                    Console.WriteLine("No extensions found in this certificate.");
                }
                else
                {
                    foreach (X509Extension extension in cert.Extensions)
                    {
                        Console.WriteLine($"  OID: {extension.Oid.FriendlyName} ({extension.Oid.Value})");
                        // You can further parse the extension.Format(true) for specific extension types
                        // For example, for Subject Alternative Name:
                        if (extension.Oid.FriendlyName == "Subject Alternative Name")
                        {
                            var sanExtension = (X509EnhancedKeyUsageExtension)extension; // Type casting might be needed
                            Console.WriteLine($"    Raw data (first 50 chars): {extension.Format(true).Substring(0, Math.Min(extension.Format(true).Length, 50))}...");
                        }
                        else
                        {
                            Console.WriteLine($"    Raw data (first 50 chars): {extension.Format(true).Substring(0, Math.Min(extension.Format(true).Length, 50))}...");
                        }
                    }
                }
            }
            else
            {
                Console.WriteLine("No certificates found in the current user's personal store.");
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine($"An error occurred: {ex.Message}");
        }
    }
}