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WINZIP Encryption - detect encrypt type

Posted on 2008-11-18
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I'm looking for a way to determine which encryption method was actually used.  As far as I can tell, WINZIP has 3 options.  The "2.0"  method, the AES 128 bit method and the AES 256 method.

A programmatic solution would be ideal, maybe something involving .NET, but I'de settle for any way of detecting it on a zip file that is already created.

The only indicator of encryption that I see is a asterisk next to the filename in the winzip dialog.  I just don't know how to determine which encryption method was used.

The reason I want to know is because I don't want anything to be encryped with the "2.0" method.

The first solution that came to mind was to use infozip to try and decrypt the file and if that worked, then I know that "2.0" was used because infozip doesn't support AES encryption, but that method isn't really a good sollution for me.
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Question by:Jeff Darling
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by:Jeff Darling
ID: 22985968
I think I just found the answer, but I'll leave this question open to the experts for a while to see if they agree or have anything to add.

http://www.winzip.com/aes_info.htm

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Kelvin_King earned 2000 total points
ID: 22985987
Most likely you'll have to dig deep into the WinZip header formats.

I personally haven't done this before (detecting the encryption type used). But this is where I would start, and I believe is the correct direction (although extremely tedious).

http://www.pkware.com/documents/casestudies/APPNOTE.TXT

The WiKi
http://en.wikipedia.org/wiki/ZIP_(file_format)#The_format_in_detail

Hope that helps
- Kelvin
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by:Kelvin_King
ID: 22986040
I found this quite useful in explaining the encryption process and some of the header content.

http://www.cs.jhu.edu/~astubble/dss/winzip.pdf
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by:Kelvin_King
ID: 22986054
>> I think I just found the answer, but I'll leave this question open to the experts for a while to see if they >> agree or have anything to add.

Yep. Agreed : )
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by:Jeff Darling
ID: 31517902
thanks for the response.  
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