C#

private static void PlaceInStore(X509Certificate2 cert)
{
    X509Store store = new X509Store(StoreName.My, StoreLocation.LocalMachine);

    try
    {
        store.Open(OpenFlags.ReadWrite);

        if (!store.Certificates.Contains(cert))
            store.Add(cert);

        int indexInStore = store.Certificates.IndexOf(cert);
        cert = store.Certificates[indexInStore];

        AddAccessToCertificate(cert, "ARCHITECT\\testuser");
    }
    finally
    {
        store.Close();
    }
}

private static void AddAccessToCertificate(X509Certificate2 cert, string user)
{
    RSACryptoServiceProvider rsa = cert.PrivateKey as RSACryptoServiceProvider;

    if (rsa != null)
    {
        string keyfilepath =
            FindKeyLocation(rsa.CspKeyContainerInfo.UniqueKeyContainerName);

        FileInfo file = new FileInfo(keyfilepath + "\\" +
            rsa.CspKeyContainerInfo.UniqueKeyContainerName);

        FileSecurity fs = file.GetAccessControl();

        NTAccount account = new NTAccount(user);
        fs.AddAccessRule(new FileSystemAccessRule(account,
        FileSystemRights.FullControl, AccessControlType.Allow));

        file.SetAccessControl(fs);
    }
}

private static string FindKeyLocation(string keyFileName)
{
    string text1 =
    Environment.GetFolderPath(Environment.SpecialFolder.CommonApplicationData);
    string text2 = text1 + @"\Microsoft\Crypto\RSA\MachineKeys";
    string[] textArray1 = Directory.GetFiles(text2, keyFileName);
    if (textArray1.Length > 0)
    {
        return text2;
    }
    string text3 =
    Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData);
    string text4 = text3 + @"\Microsoft\Crypto\RSA\";
    textArray1 = Directory.GetDirectories(text4);
    if (textArray1.Length > 0)
    {
        foreach (string text5 in textArray1)
        {
            textArray1 = Directory.GetFiles(text5, keyFileName);
            if (textArray1.Length != 0)
            {
                return text5;
            }
        }
    }
    return "Private key exists but is not accessible";
}

<br />
        private static void GiveAccessToFolder()<br />
        {<br />
            string path = @"d:\testFolder\";<br />
            DirectorySecurity ds = Directory.GetAccessControl(path);<br />
<br />
            ds.AddAccessRule(new FileSystemAccessRule("ARCHITECT\\testuser", <br />
                FileSystemRights.FullControl, AccessControlType.Allow));<br />
<br />
            Directory.SetAccessControl(path, ds);<br />
        }<br />