With a strong password of 10+ characters, mixed case, etc... Is the encryption of a Excel 2007 document secure enough to create reasonably strong defense against a brute force attack?
What encryption method does Excel 2007 employ?
According to the Microsoft whitepaper and a few other MSDN blog sources, the following specs are defined:
Older versions of Office use RC4, which is now deprecated and not recommended.
In summary, I'd say yes, with a good password this is going to be difficult to crack.
Modern GPU hash cracking tools can reach around 3.2 billion hashes per second on a powerful graphics card. With the default options, the KDF used will reduce that to roughly 64k hashes per second.
Assuming ten characters (a-z, A-Z, 0-9) you're looking at a key space of 840,000,000,000,000,000 (8.4x10^17) possible passwords, so that's around 210 thousand years before you hit a 50% likelyhood of cracking the password.
If you're storing financial information, take a look at these registry tweaks for Office 2007 SP2 that allow you to alter some security parameters. For a decent increase in security, set the
Already left a message in another topic, so just let me quote the answer:
So as you see, Excel 2007/2010 protection can be cracked instantaneously, and thus can't be considered strong any more.