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From Nick Burch <n...@torchbox.com>
Subject RE: Encryption/password protected excel/word files
Date Tue, 17 Apr 2007 13:33:06 GMT
On Tue, 17 Apr 2007, Justin Warren wrote:
> I should mention that the exceptions don't really tell if the files are 
> password protected or not. For word, I catch an 
> ArrayIndexOutOfBoundsException, or java.lang.NegativeArraySizeException. 
> I'm guessing that is not the expected behaviour.

With powerpoint, we did find one record we could look for early on that 
indicates if the file is encrypted or not. For the others, we haven't 
spotted anything suitable.

The problem is that if the file is encrypted, lots of the core records are 
there, but there data is encrytped, and hence garbage if you try to read 
it as if it wasn't. Unless we can tell very early on that a file is 
encrypted, we can't just look through the record list looking for the 
encrypted record flag, since the parent records can't be read properly. 
Instead, we must find either a absolute offset to an indicator, or one 
non encrypted record at a given location that'll have a child that tells 
you it's encrypted.


If someone encrypts both the properties and the document, it's easy, as 
you can tell at the poifs level. If they just encrypt the document, it's 
hard. See EncryptedSlideShow in hslf for an example of how to do it for 
powerpoint. Any suggestions for a similar way to do it for word or excel 
gratefully received :)

Nick

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