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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.

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migrated from serverfault.com Mar 31 '11 at 15:12

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I can never find where I saw it for reference, but it's based on the cryptographic providers you have installed on your system. Not sure how it chooses them, though –  squillman Mar 31 '11 at 15:22

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Looking at this page: http://technet.microsoft.com/en-us/library/cc179125.aspx

When Office uses CryptoAPI, the encryption algorithms depend on those that are availablein a CSP (Crypto Service Provider), which is part of the Windows operating system. The following registry key contains a list of CSPs that are installed on a computer:

HKEY_LOCAL_MACHINE/SOFTWARE/Microsoft/Cryptography/Defaults/Provider

The following CNG encryption algorithms, or any other CNG cipher extension installed on the system, can be used with Office 2010 or the 2007 Office system SP2:

AES, DES, DESX, 3DES, 3DES_112, and RC2

The following CNG hashing algorithms, or any other CNG cipher extension that is installed on the system, can be used with Office 2010 or the 2007 Office system SP2:

MD2, MD4, MD5, RIPEMD-128, RIPEMD-160, SHA-1, SHA256, SHA384, and SHA512

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. AES encryption is the strongest industry-standard algorithm that is available and was selected by the National Security Agency (NSA) to be used as the standard for the United States Government. AES encryption is supported on Windows XP SP2, Windows Vista, Windows 7, Windows Server 2003, and Windows Server 2008.

I would think maybe it uses AES 128 bit as the default.

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