How do you parse the Subject Alternate Names from an X509Certificate2?

Question

Is there an easy way to get the Subject Alternate Names from an X509Certificate2 object?

        foreach (X509Extension ext in certificate.Extensions)
               


        

Answer 1

Use the Format method of the extension for a printable version.

X509Certificate2 cert = /* your code here */;

foreach (X509Extension extension in cert.Extensions)
{
    // Create an AsnEncodedData object using the extensions information.
    AsnEncodedData asndata = new AsnEncodedData(extension.Oid, extension.RawData);
    Console.WriteLine("Extension type: {0}", extension.Oid.FriendlyName);
    Console.WriteLine("Oid value: {0}",asndata.Oid.Value);
    Console.WriteLine("Raw data length: {0} {1}", asndata.RawData.Length, Environment.NewLine);
    Console.WriteLine(asndata.Format(true));
}

Answer 2

Expanding on Minh Nguyen's Answer taking into account using OID i rewrote it as a extension

namespace MyExtensions
{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Security.Cryptography;
    using System.Security.Cryptography.X509Certificates;
    using System.Text.RegularExpressions;

    public static class X509Certificate2Extensions
    {
        private const string SubjectAlternateNameOID = "2.5.29.17";

        public static List<string> SubjectAlternativeNames(this X509Certificate2 cert)
        {
            var subjectAlternativeName = cert.Extensions.Cast<X509Extension>()
                .Where(n => n.Oid.Value == X509Certificate2Extensions.SubjectAlternateNameOID)
                .Select(n => new AsnEncodedData(n.Oid, n.RawData))
                .Select(n => n.Format(true))
                .FirstOrDefault();

            return string.IsNullOrWhiteSpace(subjectAlternativeName)
                ? new List<string>()
                : subjectAlternativeName.Split(new[] {"\r\n", "\r", "\n"}, StringSplitOptions.RemoveEmptyEntries)
                    .Select(n => Regex.Match(n, @"^DNS Name=(.+)"))
                    .Where(r => r.Success && !string.IsNullOrWhiteSpace(r.Groups[1].Value))
                    .Select(r => r.Groups[1].Value)
                    .ToList();
        }
    }
}