![]() ![]() If you digitally sign a shared workbook, Excel will not retain the digital signature because more than one person can make changes to the workbook. However, Excel versions that are earlier than Microsoft Excel 2002 do not recognize the digital signature. You can digitally sign any Excel workbook or Excel template. You can digitally sign the workbook for content and you can also code sign your VBA macro project in the same workbook. As long as the file remains signed, others will know it came from you and has not been modified.ĭigital signing a workbook is different from code signing a Visual Basic for Applications (VBA) macro project. For example, you can sign a file and other users can view the file. You can view and edit signed Excel workbooks, although you cannot modify and save a signed workbook without invalidating the signature. What happens when I use a digital signature? So, by encrypting the value instead of the data, a digital signature helps a user to verify the data was not changed. This algorithm makes it nearly impossible to change the data without changing the resulting value. The value is a number that a cryptographic algorithm generates for any data that you want to sign. Digital signatures can also help you distinguish workbooks and macros created by a reliable source from undesirable and potentially damaging workbooks or macro code (viruses).Ī digital signature is a public certificate plus the value of the signed data as encrypted by a private key. What is a digital signature?Įxcel uses digital signatures on the workbook contents to help ensure that the workbook has not been modified and saved since it was signed. When a digital certificate is used to sign a file, this ID is stored with the file in a verifiable form so that it can be displayed to a user. The digital certificate contains information about the person to whom the certificate was issued, as well as information about the certifying authority that issued it. To validate a signature, a certifying authority validates information about the creator of the file and then issues the digital certificate. They help to assure you that the file has not been tampered with.Ī digital certificate is an ID that a file carries with it. More information What is a digital certificate?ĭigital certificates and signatures help to assure you that the file that you are about to use comes from a reliable source. This ensures that you were the last person to make changes to the workbook or macro project. It has the same textual name of our company as publisher, but that's it.In Microsoft Office Excel 2003 and in later versions of Excel, you can digitally sign a workbook or code sign your macro project. "Renewing" a certificate is actually just another word for "Getting a brand new certificate". And every two years (it could have been three if we had bought the maximum length) this process has to be repeated.ĭigiCert claims this is by nature - there is really no way to get around this. So, we now have to tell our customers to again configure their PC:s to trust this certificate. It turns out that the "renewed" certificate is actually a brand new certificate, with (as far as I understand) no connection to the previous certificate, the one that has been trusted. Apparently, this new certificate isn't trusted. To test the certificate, I just signed a new Excel document with the renewed certificate, uploaded it to one of our customers and tested it. However, our code signing certificate just expired after two years, so we "renewed" it. This has the effect that "our" documents are now opened and VBA-code run without warning. I don't know exactly how this was done, but GPO:s were involved. add the certificate to "Trusted publishers" on their PC:s). Although they could click "Enable content" to make the code run, they thought it was a bit tiresome to do this many times a day.Ībout a year ago, we thus started to instruct these customers to configure their computers to trust our certificate (i.e. This is a good thing, security wise, but some of our customers' end-users complained. The default macro settings in Excel (which all our customers stick to) will prompt the user with a security warning, even if the document is digitally signed. Before delivering the documents to our customers, we sign the documents with our code signing certificate. Much longer: We develop (among other things) Excel documents for a number of customers. Short: Is there anyway to trust a certificate or publisher, so that the trust remains even after the certificate has expired? ![]()
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11/22/2023 02:15:04 am
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