find certificate on smartcard currently on reader

Question

I am using Visual Studio 2013 (C#) to digitally sign document using certificate from smartcard. I cannot identify certificate currently inserted in the card reader :(

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Answer 1

I was wondering why you do foreach through all certificates in a store when you know cert subject. My suggestion would be:

public static byte[] Sign(Stream inData, string certSubject)
{

    // Access Personal (MY) certificate store of current user
    X509Store my = new X509Store(StoreName.My, StoreLocation.CurrentUser);
    my.Open(OpenFlags.ReadOnly | OpenFlags.OpenExistingOnly);

    var foundCerts = my.Certificates.Find(X509FindType.FindBySubjectName, certSubject, true);
    if (foundCerts.Count == 0)
        throw new Exception("No valid cert was found");

    var cert = foundCerts[0];
    RSACryptoServiceProvider csp = null;
    // let us assume that certSubject is unique
    if (cert.HasPrivateKey)
    {
        csp = (RSACryptoServiceProvider)cert.PrivateKey;
        if (csp.CspKeyContainerInfo.HardwareDevice)
            Console.WriteLine("hardware");
        Console.WriteLine(cert.ToString());
    }
    else
    {
        throw new Exception("No private key assigned to this certificate");
    }

    // Hash the data
    SHA1Managed sha1 = new SHA1Managed();
    byte[] hash = sha1.ComputeHash(inData);

    // Sign the hash
    return csp.SignHash(hash, CryptoConfig.MapNameToOID("SHA1"));
}

If you don't know exact subject or are expecting to find another certificate with this subject this will probably not work for you.