Microsoft Office Tutorials and References
In Depth Information
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 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’ll use the selfcert.exe
Microsoft Office accessory program to generate a certificate with which to perform the exercise
at the end of 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 verify that the contents
of the document haven’t changed since it was signed.
To create a digital certificate that you can use as a demonstration, open the Start menu,
click All Programs, click Microsoft Office, click Microsoft Office 2010 Tools, and then click
Digital Certificate For VBA Projects. In the Create Digital Certificate dialog box, type a
name for your certificate and click OK to have the program create your trial certificate.
Then, in Excel, click the File tab and on the Info page of the Backstage view, click Protect
Workbook and then click Add A Digital Signature. In the Sign dialog box, type your
purpose for signing the document, and then click Sign to sign your workbook.
Tip After you click Add A Digital Signature, Excel displays a dialog box, indicating 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. To bypass the message, click OK; to
prevent the dialog box from appearing again, select the Don’t Show This Message Again check
box, and then click OK.
If you have several certificates from which to choose, and the desired certificate doesn’t
appear in the Sign dialog box, you can click Change to display the Select Certificate
dialog box. In the Select Certificate dialog box, click the certificate with which you
want to sign the workbook, and then click OK. The Select Certificate dialog box closes,
and the certificate with which you signed the workbook appears in the Sign dialog
box. As before, click Sign to sign your document by using the digital certificate.
In this exercise, you’ll create a digital certificate and digitally sign a workbook by using
the certificate.
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