(Mono C#) Load Certificate from Smart Card by Key Usage

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You may have a smartcard or USB token that contains only 2 certificates, one for signing, and one for authentication, and you wish to load the certificate for signing. This example demonstrates how to load the 1st certificate found on a smartcard that matches the intended key usage.

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// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

Chilkat.Cert cert = new Chilkat.Cert();

// If you know the smart card PIN, set it prior to loading from the smartcard/USB token.
cert.SmartCardPin = "12345678";

// To load a certificate matching an intended key usage, specify the type of usage as shown below.
// 
// The possible key usage keywords are:
// 
// digitalsignature
// Use when the public key is used with a digital signature mechanism to support security services other than non-repudiation, certificate signing, or CRL signing. 
// A digital signature is often used for entity authentication and data origin authentication with integrity.

// nonrepudiation
// When a digital certificate's key usage includes "nonrepudiation," it implies that the certificate and its associated private key can be used to 
// create digital signatures that provide proof of the origin and integrity of the signed data, and the signer cannot later deny having signed the data.

// Other less common usages:

// certificatesigning
// keyencipherment
// dataencipherment
// crlsigning
// secureemail
// serverauthentication
// clientauthentication
// codesigning
// timestamping

bool success = cert.LoadFromSmartcard("keyusage=nonrepudiation");
if (success == false) {
    Debug.WriteLine(cert.LastErrorText);
    Debug.WriteLine("Certificate not loaded.");
    return;
}

Debug.WriteLine("Found: " + cert.SubjectDN + " serial=" + cert.SerialNumber);