Certificates from SmartCard in C#

Question

How can I ensure to I am accesing the Certificates from my SmartCard and not form my personal certificate store in c#? and How can I make my RSACryptoProvider to utilize my smart card certificate private key?

thanks

Wally

Answer 1

Sometimes, especially if you are not using default key container name on the smart card (recommended by Microsoft), certificates are not copied to local certificate store. The solution is to use crypto api to access the key with KP_CERTIFICATE, construct certificate from the retrieved data, and assign it a new RSACryptoServiceProvider constructed using your own key container name.

The pseudo C# code follows:

int reti = CryptoApi.CryptGetUserKey(_hprovider, keytype, ref userKey);

if (reti)
{
    reti =CryptoApi.CryptGetKeyParam(_userKey, KP_CERTIFICATE, ref  pbdata, ref pwddatalen, 0);
}

if (reti || pwddatalen>0)
{
    byte[] data = new byte[pwddatalen];
    ret  = CryptoApi.CryptGetKeyParam(_userKey, KP_CERTIFICATE, data, ref pwddatalen, 0);
    if (ret) 
    {
        X509Certificate2 c = new X509Certificate2(data);
        X509Store store = new X509Store(StoreName.My, StoreLocation.CurrentUser);
        store.Open(OpenFlags.ReadOnly);
        X509Certificate2Collection col = store.Certificates.Find(X509FindType.FindByThumbprint, c.Thumbprint, validonly);
        store.Close();

        if (col.Count != 1) 
        {
            //not found in store - CSP didn't copy it
            c.PrivateKey = PrivateKey(keytype);
            return c;
        }
        else
        {
            return col[0];
        }
    }
}


private RSACryptoServiceProvider PrivateKey (KeyType keytype)
{
    CspParameters csparms = new CspParameters();
    csparms.KeyContainerName = _containerName;
    csparms.ProviderName = _provider;
    csparms.ProviderType = 1;
    csparms.Flags = CspProviderFlags.UseMachineKeyStore | CspProviderFlags.UseExistingKey;
    csparms.KeyNumber = (int)keytype;

    return new RSACryptoServiceProvider(csparms);
}