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I have protected sheets in Excel 2013 and sent the the. To ensure sheets are protected with the highest level of security offered by Excel, protect them in Excel 2013 or later, even if the workbooks were originally created or are being used in Excel 2007-2010. Saving a 2013 workbook as a 2003 file, removes the strong sheet protection hashes set by Excel 2013, as the XLS file format is not compatible with the OpenXML file standard! Obviously any features not supported by Excel 2003 will be lost or degraded as well.A workbook with a sheet protected in Excel 2013 or 2016 will only be vulnerable again to a brute force attack, if it is saved after the sheet has been unprotected & re-protected in Excel 2007-2010.

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If a sheet is protected again in Excel 2007-2010, the secure SHA512 hash will be replaced by a weak, outdated hash, which is easy to crack using VBA code circulating around the web. This cryptographic information is maintained while the workbook is used in Excel 2007-2010, as long as sheets are not unprotected. Protect sheets in Excel 2013 or 2016, use the workbook in Excel 2007-2010, but do not unprotect or protect these sheets again in any version earlier than 2013.Ī SHA512 secure hash along with a salt value is stored for every sheet protected in Excel 2013. If you look carefully inside the sheetProtection XML node (image above), you will notice several protection attributes: saltValue, hashValue and algorithmName.ĭo you want to protect sheets or workbook structure in a secure way that cannot be hacked by a VBA brute force attack running in Excel 2007-2010? Hashes are randomized with a use of a random string called salt, which does not need to be secret. In cryptography, salt is random data that is used as an additional input (along with the password) to the one-way algorithm that hashes a password. So even when the same password is hashed multiple times, the hashes are not the same! Excel 2013 prevents such attacks by randomizing each hash with the use of a salt value. One approach to crack hashes are cryptographic lookup and rainbow tables. However, the SHA512 hash algorithm used Excel 2013 is quite secure. These 16-bit long plain hashes are very easy to hack, so working passwords can be recovered fast. Here is a look inside an OpenXML file saved in Excel 2013:Įxcel versions up-to 2010 used an outdated hashing algorithm. In case you are not aware, read about the differences between Office 365 and Office 2016.

So working passwords cannot be recovered. It is impossible to find multiple passwords that share the same hash value in Excel 2013, as was the case with Excel up to Office 2010 version.

Microsof office 365 foce quit for mac cracked#

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Have you noticed that sheet protection VBA methods run much slower in Excel 20? That's because the new complex hashing algorithm takes longer to compute. For single sheet manual protection operations the delay is barely noticeable, but when add-ins or macros unlock/lock sheets in bulk, the delay can be significant. Office 2013 has silently introduced security changes in order to strengthen Excel protection!