April 2006
Beginner
1114 pages
98h 16m
English
Content preview from Programming Excel with VBA and .NETBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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When Signatures Expire
Digital signatures have expiration dates to help ensure their authenticity. When a user opens a signed Excel file after the signature’s expiration date, she sees a security warning saying that the signature has expired. To avoid this problem, you can timestamp signatures so that Excel compares the signature expiration to the timestamp rather than the current date.
Unfortunately, timestamps aren’t automatic in Excel. In order to get it working, you need to edit your system registry to use a timestamp service provided by your certificate authority. For example, the following registry entries configure your system to use Verisign’s timestamp service (timestamp.reg):
Windows Registry Editor Version 5.00 [HKEY_CURRENT_USER\Software\Microsoft\VBA\Security] [HKEY_CURRENT_USER\Software\Microsoft\VBA\Security\TimeStampRetryCount] @="10" [HKEY_CURRENT_USER\Software\Microsoft\VBA\Security\TimeStampRetryDelay] @="10" [HKEY_CURRENT_USER\Software\Microsoft\VBA\Security\TimpeStampURL] @="http://timestamp.verisign.com/scripts/timstamp.dll"
To merge these entries into your system registry, double-click on the sample file timestamp.reg in Windows Explorer. Before you rely on timestamps, you should test this procedure on your machine by signing code in an Excel file, closing it, changing your system date, then reopening the file in Excel. Please contact your certificate authority if you have problems.
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