Page 484 - Excel 2013 All-in-One For Dummies

466 Preparing a Workbook for Distribution
✦ Add an invisible signature to the workbook indicated by the Digital Signature icon on the status bar and metadata added to the document that verifies the source of the workbook.
By adding a digital signature, you warrant the following three things about the Excel workbook you’re about to distribute:
✦ Authenticity: The person who signs the Excel workbook is the person he says he is (and not somebody else posing as the signer).
✦ Integrity: The content of the file has not been modified in any way since the workbook was digitally signed.
✦ Nonrepudiation: The signer stands behind the content of the workbook and vouches for its origin.
To make these assurances, the digital signature you add to the workbook must be valid in the following ways:
✦ The certificate that is associated with the digital signature must be issued to the signing publisher by a reputable certificate authority.
✦ The certificate must be current and valid.
✦ The signing publisher must be deemed trustworthy.
Microsoft partners such as ARX CoSign Digital Signatures, Avoco secure- 2trust, or GlobalSign offer digital ID services to which you can subscribe. As reputable certificate authorities, their protection services vouch for your trustworthiness as a signing publisher and the currency of the certificates associated with your digital signatures. In addition, they enable you to set the permissions for the workbook that determine who can open the docu- ment and how they can use it. To sign up with one of these services, choose the Add Signature Services option from the Signature Line button’s drop- down menu and then follow the links on the Available Digital IDs Web page. Note that as a Windows Live subscriber to Office 365, you can also issue a certificate of authenticity using your Windows Live ID (as I did in Figure 3-4).
To add a digital signature to your finalized workbook, you follow these steps:
1. Inspect the worksheet data, save all final changes in the workbook file, and then position the cell pointer in a blank cell in the vicinity where you want the signature line graphic object to appear.
Excel adds the signature line graphic object in the area containing the cell pointer. If you don’t move the cell cursor to a blank area, you may have to move the signature line graphic so that graphic’s box doesn’t obscure existing worksheet data or other graphics or embedded charts.