[Owncloud] help needed with encryption and corruped files

[Frank Karlitschek]

On 15.06.2012, at 01:29, Victor Dubiniuk <victor.dubiniuk at gmail.com> wrote:

> Hi ownClouders,
> 
> I'm not an encryption guru but I went further.
> Blowfish encrypt method pads the input data with 0x00 in order to make their length multiple of 8.
> Then it packs them into unsigned long:
>     pack("N2", $Xl, $Xr);
> 
>  *.exe files are already aligned that's why removing rtrim has no effect on their decryption. 
> From the other hand, trimming is required for any text file or string as it is padded with 0x00 and corrupted if it's length is not multiple of 8.
> 
> I'm not sure how to solve this puzzle right now.
> Is it worth to store the original file size before encryption and trim the excessive bytes for the decrypted file to match this size?

@Robin: Can you have a look here? I think the algorithm might be from you.

Frank


> 
> ---
> Victor Dubiniuk
> 
> 
> On Wed, Jun 13, 2012 at 7:05 PM, Frank Karlitschek <frank at owncloud.org> wrote:
> Wow.
> Very good catch.
> 
> Now the question is why was the rtrim here in the first place. I can´t remember if this is my code from last summer ob from someone else :-)
> 
> 
> Frank
> 
> 
> On 13.06.2012, at 17:18, Victor Dubiniuk <victor.dubiniuk at gmail.com> wrote:
> 
> > My apologies for sending the incomplete message.
> >
> > I used 4.0.2 to debug the encryption and found that the problem is in the OC_Crypt::decrypt  - it strips all 0x00 characters at the 8KB block boundary.
> > Please check the encryption with the attached files. One has 32 of 0x00 inside and another one is the same but has 0x05 at the 7th position.
> >
> > When I change apps/files_encryption/lib/crypt.php  line #136
> >               return rtrim($data, "\0");
> > to
> >               return $data;
> >
> > the file is decrypted correctly except the fact that it's last block is padded with 0x00. (Tested on *.exe ~ 7MB)
> >
> > ---
> > Victor Dubiniuk
> >
> >
> > On Wed, Jun 13, 2012 at 4:45 AM, Michael Gapczynski <mtgap at owncloud.com> wrote:
> > On Tuesday, June 12, 2012 12:52:06 PM Klaas Freitag wrote:
> > > On 04.06.2012 18:33, Klaas Freitag wrote:
> > > > On 04.06.2012 18:13, Frank Karlitschek wrote:
> > > >> Hi,
> > > >>
> > > >> we have a very evil bug report about corrupted files together with the
> > > >> encryption app.
> > > >>
> > > >> http://bugs.owncloud.org/thebuggenie/owncloud/issues/oc-912
> > > >> http://forum.owncloud.org/viewtopic.php?f=3&t=2726
> > > >>
> > > >> Everything works for me and I can´t find the problem
> > > >> Can someone help me with reproducing it?
> > > >
> > > > I can reproduce it with a Firefox on Linux and on Windows 7. I have
> > > > master running from this morning.
> > >
> > > Frank, do you think that
> > > http://bugs.owncloud.org/thebuggenie/owncloud/issues/oc-669
> > > can be related to this problem? Is there a fix already for #912?
> > >
> > > Thanks,
> > >
> > > Klaas
> >
> > It seems that binary data has problems going through the encryption. I did
> > some research and read that base64_encode()/decode() should allow binary files
> > to be encrypted. My attempts to encode and decode the data with base64 still
> > result in corrupted binary files.
> >
> > http://bytes.com/topic/php/answers/8958-binary-encryption
> >
> > http://stackoverflow.com/questions/6033972/encrypting-files-with-php-mcrypt-
> > is-corrupting-docx-and-other-microsoft-office
> >
> > http://www.itnewb.com/tutorial/PHP-Encryption-Decryption-Using-the-MCrypt-
> > Library-libmcrypt
> >
> >
> >
> > Michael
> > _______________________________________________
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> > https://mail.kde.org/mailman/listinfo/owncloud
> >
> >
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> > https://mail.kde.org/mailman/listinfo/owncloud
> 
> 
> 
> 
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