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Failure when Unzipping zip file that uses DEFLATE64

Jul 22, 2011 at 1:41 PM

I am trying to unzip a file that uses  AES128 encryption.  I try passing the password in code but I keep getting an error that  *.zip uses an unsupported compression method.  Can I not unzip this file using dotnetzip?


Jul 23, 2011 at 3:23 PM

From the error message, probably not.

What is the exact error message you see?

AES encryption is distinct from the compression method.  In a zip file, entries can be encrypted, or compressed, or both.  For encryption, DotNetZip handles PKZIP encryption or AES encryption.  There are other encryption possibilities in zip files, which DotNetZip does not handle.  For compression, DotNetZip handles DEFLATE.  There are other compression methods that DotNetZip does not handle (eg, BZIP2, others). 

It's possible that you have a zip file that is compressed with a compression method that is not supported by DotNetZip (eg BZIP2) and then encrypted with AES128.  In that case DotNetZip would not be able to extract the entries.


Jul 24, 2011 at 9:03 PM

Thanks for the reply.  The message I get is Entry db.bak uses an unsupported compression method (0x09, Deflate64)  I am kind of at a loss here how to do this programatically.

Jul 25, 2011 at 3:31 PM

DotNetZip does not support DEFLATE64.   It has nothing to do with encryption, or passwords, or AES128. DEFLATE64 is a compression method.

DotNetZip cannot extract entries in a zip file that are compressed with DEFLATE64.  Once I looked into adding this capability into DotNetZip, but DEFLATE64 is proprietary, specified only by PKWare, and I think it is not well-supported or broadly used.  So I decided to not try to do the work.

(ps: not that you asked, but since I mentioned bzip2.... I thought I would add here for posterity's sake that I am right now working on adding BZIP2 compression to DotNetZip.   Unlike Deflate64, BZip2 is not proprietary; it is broadly supported; and it is broadly used elsewhere (though used less commonly within ZIP files).   The BZIP2 compressor is currently working nicely, and tests with WinZip show that it is fully compatible.  but I haven't produced a binary release with this, yet. The first release with the bzip2 capability will be v1.9.1.6. Coming soon.)

Nov 20, 2013 at 3:44 PM

I get the same error message:
Entry FBN_BETALING_20130628.csv uses an unsupported compression method (0x09, Deflate64)

I don't get it, I zip a bunch of files from a directory with the windows send to compressed folder way.

Does windows uses DEFLATE64??
Feb 4, 2014 at 5:10 PM
I get the same Deflate64 error as well. My client is using windows explorer - Send to (compressed) zipped folder. When I use either the 4.5 .Net Framework or DotNetZip utility, I get the same non supported Deflate64 error. I checked the machines where the files are being zipped, thinking that maybe the .zip extension was associated with a 3rd party compression application, but that's not the case.

One guess is that the error message is bogus and the real reason has to do with the size of the file being extracted. In my case, it's over 2 gig in size.

Just noticed how old the prior post is. Regardless, there's still no resolution to the prior post, or is there?