Microsoft Office Tutorials and References
In Depth Information
Authenticating workbooks
Authenticating workbooks
The unfortunate reality of exchanging files over networks, especially over the Internet, is
that you need to be sure you know the origin of the files you’re working with. One way an
organization can guard against files with viruses or substitute data is to authenticate every
workbook by using a digital signature. A digital signature is a character string created by
combining a user’s unique secret digital signature file mathematically with the contents of
the workbook, which programs such as Excel can recognize and use to verify the identity of
the user who signed the file. A good analogy for a digital signature is a wax seal, which was
used for thousands of years to verify the integrity and origin of a document.
TIP The technical details of and procedure for managing digital certificates are beyond
the scope of this topic, but your network administrator should be able to create a digital
certificate for you. You can also directly purchase a digital signature from a third party,
which can usually be renewed annually for a small fee. For the purposes of this topic, you
can use the selfcert.exe Microsoft Office accessory program to generate a certificate with
which to perform the exercise in this topic. This type of certificate is useful for certifying a
document as part of a demonstration, but other users will not accept it as a valid certificate.
To create a digital certificate that you can use as a demonstration, navigate to the folder
that contains your Office 2013 program files. Whether you have the selfcert.exe file and the
specific folder it’s in if you do have it depends on your computer’s configuration, the drive
onto which you installed Office 2013, and whether you installed all available files when you
installed Office 2013. One typical folder is C:\Program Files (x86)\Microsoft Office\Office15.
In that folder, which contains a large number of files, you will find the selfcert.exe program.
Double-click the program to run it.
In the Create Digital Certificate dialog box, enter a name for your certificate and click OK
to have the program create your trial certificate. Then, in Excel, display the Info page of
the Backstage view, click Protect Workbook, and click Add A Digital Signature. In the Sign
dialog box, enter your purpose for signing the document, select the certificate you want to
use, and then click Sign to sign your workbook.
IMPORTANT After you click Add A Digital Signature, Excel checks your computer for usable
digital certificates. If it can’t find one, Excel displays a dialog box that indicates that you can
buy digital signatures from third-party providers. To get information about those services, click
the Signature Services From The Office Marketplace button. You won’t be able to add a digital
signature to a file until you acquire a digital certificate, either by generating a test certificate
using the included selfcert.exe program or by purchasing one through a third-party vendor.
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