Excel 2003 Programming: A Developer's Notebook

Add Digital Signatures

A digital signature identifies the author of the content or the macros contained in a workbook, template, or add-in. You add a digital signature as the last step before you distribute a file. When others open the a signed file they can see who the author is and therefore decide whether the information in the file is authentic and whether any macros it contains are safe to run.

The signature is overwritten any time a file is saved. Therefore, no one can open a signed file, make changes, save, then send the file on still bearing your signature. Workbooks and macros are signed separately even though they are contained in a single file. If you want to distribute a signed workbook containing macros, you must sign the macros first, then sign the workbook.

Get a Digital Certificate

Before you can sign a document, you must first get a digital certificate, which is also sometimes called a digital ID or simply a certificate . There are two ways get a digital certificate: create one yourself or purchase one from a Certificate Authority (CA). Self-created signatures are only valid on the machine where they were created, so they are for macros that won’t be distributed. CA-created signatures are available from vendors such as Verisign, Inc. and CAcert.org.

To create a digital certificate yourself:

1. From the Windows Programs menu, choose Microsoft Office → Microsoft Office Tools → Digital Certificate for VBA Projects. Windows runs SelfCert.exe