CODEWITHSUNDEEP
c#.netx509certificatex509x509certificate2
J4N
J4N

Reputation: 20761

How to build a self-certified x509 certificate that is valid in my computer

I need to build a self-signed x509 certificate that is recognized valid on my computer through C# code.

If required, this can be ran with admin privileges.

My current code is the following

public static X509Certificate2 GenerateCertificate(string name)
{
    string subjectName = $"CN={name}";
    using (RSA rsa = RSA.Create(2048))
    {
        CertificateRequest req = new CertificateRequest(
            subjectName,
            rsa,
            HashAlgorithmName.SHA256,
            RSASignaturePadding.Pkcs1);

        req.CertificateExtensions.Add(
            new X509BasicConstraintsExtension(false, false, 0, false));

        req.CertificateExtensions.Add(
            new X509KeyUsageExtension(
                X509KeyUsageFlags.DigitalSignature | X509KeyUsageFlags.NonRepudiation,
                false));

        req.CertificateExtensions.Add(
            new X509EnhancedKeyUsageExtension(
                new OidCollection
                {
                    new Oid("1.3.6.1.5.5.7.3.8")
                },
                true));

        req.CertificateExtensions.Add(
            new X509SubjectKeyIdentifierExtension(req.PublicKey, false));

        return req.CreateSelfSigned(
            DateTimeOffset.UtcNow.AddDays(-1),
            DateTimeOffset.UtcNow.AddYears(50));
    }
}

public static X509Certificate2 GetOrCreateCertificate(string serverName)
{
    using (X509Store store = new X509Store(StoreLocation.LocalMachine))
    {
        X509Certificate2 certificate;
        store.Open(OpenFlags.ReadWrite);
        X509Certificate2Collection certificateCollection = store.Certificates.Find(X509FindType.FindBySubjectName, serverName, true);//With true, my certificates are not returned
        if (certificateCollection.Count > 0)
        {
            certificate = certificateCollection[0];
            return certificate;
        }

        certificate = GenerateCertificate(serverName);
        store.Add(certificate);

        return certificate;
    }
}

Currently, if I go in the windows MMC, certificate snap-in, I see the certificate, but it is considered as invalid.

What did I miss?

EDIT

Upvotes: 0

Views: 815

Answers (1)

bartonjs
bartonjs

Reputation: 33266

The problem that you're having seems to be that the system doesn't trust the new certificate.

In order to be trusted, the root of a certificate chain must be represented in one of the following stores:

  • LocalMachine\Root
  • LocalMachine\ThirdPartyRoot
  • CurrentUser\Root

(there are also some other stores involved, for domain-managed root authorities)

So after you do

certificate = GenerateCertificate(serverName);
store.Add(certificate);

You will also want to do

using (X509Store rootStore = new X509Store(StoreName.Root, StoreLocation.LocalMachine))
using (X509Certificate2 withoutPrivateKey = new X509Certificate2(certificate.RawData))
{
    rootStore.Open(OpenFlags.ReadWrite);
    rootStore.Add(withoutPrivateKey);
}

Now the system will be able to verify the (single-node) chain up to a trusted certificate, and the validOnly: true constraint on Find will consider the certificate to be "valid" (which, for that method, means chain-trusted and not expired).

Upvotes: 1

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