How to: Work with Digital Signatures Using the InfoPath 2003 Object Model

The InfoPath 2003-compatible object model provides features for working with digital signatures programmatically.

Digital Signature Features

The digital signatures features available in InfoPath allow you to:

• Enable signatures for the entire form, or for specific sets of data in the form that can be signed separately.

• Specify, for each set of data that can be signed, whether a single signature or multiple signatures are allowed and what their relationship will be. For example, you can specify whether they are parallel co-signatures or whether each new signature countersigns all the earlier signatures.

• Specify a message to be shown to form users as they sign the form.

• Insert and see a signature in the document.

• View verifiable non-repudiation information that has been added to each signature for increased security. This additional information, which includes a view of the form as it was presented to each signer, is part of the signature and cannot be removed without invalidating the signature. At any time, you can recall this data by clicking on the signature in the form to display the Verify Digital Signature dialog box.

• Take advantage of an object model for working with digital signatures. Add custom information to the signature block in fully trusted forms through the digital signature object model.

Overview of the Digital Signatures Object Model

Events

The object model for digital signatures provides the following event.

The OnSign event returns a reference to the SignEventObject object, which provides the following properties.

Collections and Objects

The object model for digital signatures provides the following collections.

The object model for digital signatures provides the following objects.

Working with Digital Signatures Programmatically

The InfoPath 2003-compatible object model provides members for interacting with digital signatures programmatically. In particular, fully-trusted forms can add custom information to the signature block before it is committed, according to the following timeline:

1. User chooses to add a digital signature to a form.

2. The first panel of the Digital Signature Wizard is displayed.

3. The OnSign event for the selected data represented by the SignedDataBlockObject object is raised, and the Sign method of SignedDataBlockObject and the Create method of the SignaturesCollection collection are executed.

4. Any optional custom actions are executed.

5. The Sign method of the SignatureObject is executed.

6. Second and third panes of the wizard are displayed for selecting a certificate to sign with and to enter comments.

7. The non-repudiation information is displayed (which can be viewed later with the Verify Digital Signature dialog box).

8. When the Sign button is clicked, the signature is added to collection of signatures for the form.

The following example invokes the Sign dialog box and countersigns the signature with a timestamp value retrieved from a trusted timestamp service.

[InfoPathEventHandler(EventType=InfoPathEventType.OnSign)]
public void OnSign(SignEvent e)
{
    Signature signature = e.SignedDataBlock.Signatures.Create();
    // Invoke the Sign dialog box to sign the data block.
    signature.Sign();
    // Countersign the signature with a trusted timestamp
    // Get the XML node storing the signature block
    IXMLDOMNode oNodeSig = signature.SignatureBlockXmlNode;
    IXMLDOMNode oNodeSigValue = oNodeSig.selectSingleNode(".//*[local-name(.)='signatureValue']");
    // Get timestamp from a trusted timestamp service (fictitious).
    MyTrustedTimeStampService s = new MyTrustedTimeStampService();
    string strVerifiedTimeStamp = s.AddTimeStamp(oNodeSigValue.text);
    
    //Add the value returned from the timestamp service to the 
    //unsigned part of the signature block
    IXMLDOMNode oNodeObj = oNodeSig.selectSingleNode(".//*[local-name(.)='Object']");
    IXMLDOMNode oNode = oNodeObj.cloneNode(false);
    oNode.text = strVerifiedTimeStamp;
    oNodeObj.parentNode.appendChild(oNode);

    e.ReturnStatus = true;
}