What algorithm does Microsoft Office 2010 use for encryption?

Question

Does it use the standard AES 128bit key for encryption? I've searched a lot on Google, but I still haven't found the algorithm is uses for encrypting.

I'm encrypting a PowerPoint file.

Solution 1

This technet article confirms that the defaults are AES 128-bit key, SHA1, CBC.

Although there are Office 2010 settings to change how encryption is performed, when you encrypt Open XML Format files (.docx, .xslx, .pptx, and so on) the default values — AES (Advanced Encryption Standard), 128-bit key length, SHA1, and CBC (cipher block chaining) — provide strong encryption and should be fine for most organizations.

It is important to note, however, that encryption is export controlled and that all versions of windows may not have all cryptographic providers installed. The article also mentions that you can see which Cryptographic Service Providers are installed by checking the registry key:

HKEY_LOCAL_MACHINE/SOFTWARE/Microsoft/Cryptography/Defaults/Provider

Solution 2

These MS docs specify completely the different algorithms, and also the differences between the different versions, etc. For Office 2010 AES-128 with CBC is used, but Office 2007 used AES-128 in ECB mode, and before that, RC4 was used. So it also depends on how compatible you want to be (what can the receiving party still decrypt?).