怎么获取数字证书中的"颁发机构密钥标标识符"

using System.Security.Cryptography;using System.Security.Cryptography.X509Certificates;   protected void Page_Load(object sender, EventArgs e)    {        X509Store store = new X509Store(StoreLocation.CurrentUser);        store.Open(OpenFlags.ReadOnly);        X509Certificate2Collection certCollection = store.Certificates;        foreach (X509Certificate2 c in certCollection)        {            RSACryptoServiceProvider privatekey = (RSACryptoServiceProvider)c.PrivateKey;        }    }