Weak/Broken: MS office encryption for Word & Excel
Bruce Schneier mentioned this a few days ago, and while the topic of misusing an encryption protocol is not new, I feel it bears repeating.
Hongjun Wu of the Institute for Infocomm Research, Singapore has written an informative paper entitled The Misuse of RC4 in Microsoft Word and Excel. He pretty much sums up the whole point right there.
The distilled version is this: if you have two versions of an encrypted Word or Excel document, you can compare them to recover the data. This is done by XORing the two documents against each other and then using some basic pattern analysis. Not your typical script kiddie fare, but not too difficult either, if one applies some time and effort to learning a few skills.
Quote:
It's an amateur crypto mistake.
I like how Bruce put's it, and he's right. What is trully dissapointing is the fact that MS was stung by this before...5 years ago, with their NT Syskey encryption of the SAM. Two whole OS versions and god knows HOW many Office versions later, and this is still an issue? Someone in MS product development and engineering should be fired, IMNSHO.