[Owncloud] help needed with encryption and corruped files

[Frank Karlitschek]

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 $data;
> 
> the file is decrypted correctly except the fact that it's last block is padded with 0x00. (Tested on *.exe ~ 7MB)
> 
> ---
> Victor Dubiniuk
> 
> On Wed, Jun 13, 2012 at 6:07 PM, Victor Dubiniuk <victor.dubiniuk at gmail.com> wrote:
> Hi all,
> 
> I used 4.0.  and found that the problem is in the  OC_Crypt::decrypt
> it strips all 0x00 characters at the block boundary. 
> Please check with the attached files.
> One has 32 of 0x00 inside and another one - 
> 
> When I change apps/files_encryption/lib/crypt.php  line #136
> 		return rtrim($data, "\0");
> to 
> 		return $data;
> 
> the file is decrypted correctly except the fact that it's last block is padded with 0x00.
> 
> I hope that it will be helpful.
> 
> 
> ---
> 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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