Ya. that makes sense. Let me revisit my design a bit then and rethink over the idea of encryption. 

Nonetheless.. I  appreciate your prompt, detailed, technical responses and that makes me and my team more confident in using BaseX in present and similar future scenarios. I'd keep you all posted on the progress we make on this proof of concept and the pathway to productize this.

Regards,
N.D.

On Fri, Sep 26, 2014 at 1:34 PM, Dirk Kirsten <dk@basex.org> wrote:
Hello Nilanjan,

thanks; this explanation helped and I think I now fully understand your requirements and application. Still, I would argue that encryption is not necessary and not what you really need.

You would use encryption is not allowed to see an information. However, in your case you want your use to use this information, but not the plain file but via your application instead. So this is an access control problem, not an encryption problem.

How do you plan to read these XML files later? I would guess you use BaseX for this as well (and if not I would recommend it for this scenario). So instead of just sending the user the zipped version of the XML files, require them to load this XML data in BaseX. As Marco has pointed out, the XML files are then parsed and stored in a binary format. If you open them using a text editor, you will just see scrambled data. The same would be true for opening an encrypted zip file, so there is really no difference in terms of tempering from your users.

You could encrypt parts of your XML using our cryptographic module (http://docs.basex.org/wiki/Cryptographic_Module), although this suffers from the same problem as your original encryption idea: It would not be truly secure, because you have to store the key somewhere. As you want to decrypt the data in some point, you need the key. As you have no online connection, the key has to be stored where the application is stored, i.e. your user will always be able to access this key (it might be more complicated if you obfuscate it, but it adds no theoretical value). So if it adds nothing, why bother using it?

Cheers,
Dirk

On 09/25/2014 07:45 PM, Nilanjan Dutta wrote:
> These XML files actually would contain some algorithm which would help him
> to decode and analyse some log files. So the necessity of making these XML
> file encrypted is even more important for us.
>
> Regards,
> N.D.
>
> On Thu, Sep 25, 2014 at 11:13 PM, Nilanjan Dutta <
> nilanjan.dutta.india@gmail.com> wrote:
>
> > Thanks again for the detailed response.
> >
> > Yes Dirk, in this data transfer module of the project use case is like
> > this: We create some data (in this case it is that xml) in server and dump
> > it into the client machine. This XML data he uses to analyse some log files
> > which he would mostly get from a remote location . So for him, this XML
> > data works like a knowledge-base to analyse that log file. During this
> > analysis he may or may not be connected to the internet (he may even choose
> > to be offline-as per requirement) and hence we need to enable him having
> > the XML data in his local always. As in when we get any update on the XML
> > data we use this module to automatically update his/her local knowledge
> > base through that service (wcf) too.
> >
> > I also understand that these files are not accessible in normal way
> > without BaseX, but to avoid any data loss by any means, wanted this to be
> > encrypted in such a way that without programmatic intervention they can
> > never be opened.
> >
> > Regards,
> > N.D.
> >
> > On Thu, Sep 25, 2014 at 6:11 PM, Dirk Kirsten <dk@basex.org> wrote:
> >
> >> So, if I understand you correctly, you have not a real client/server
> >> application in a way that your application simply sends queries to a
> >> server, but instead your server does some processing and then exports
> >> files to a user. Is this correct?
> >>
> >> And you want these processed XML files to be zipped and encrypted? I
> >> think our ZIP module (see https://docs.basex.org/wiki/ZIP_Module) does
> >> not support encryption (this could be an interesting extension for the
> >> EXPath spec), so you might want to use some 3rd party tool to put your
> >> exported XML files into an encrypted zip file.
> >>
> >> I am quite surprised by this unusual environment. Is there any reason
> >> why you want your XML data to be exported to the user instead of simply
> >> having all your data at the server and the client just accessing the
> >> data? I could only imagine this usefule in a scenario with limited
> >> connectivity to the database server (e.g. a mobile application).
> >>
> >> On 25/09/14 14:33, Nilanjan Dutta wrote:
> >>> Sorry if I'm not able to clear the confusion.
> >>>
> >>> It's not the source XML files which I want to encrypt. I want to encrypt
> >>> the resulting DB files -which I'd get after feeding the original XML
> >> file
> >>> to BaseX -instead. And I don't want my users to be able to access those
> >> DB
> >>> files when it reaches to the client machine and stays there.  Server he
> >> can
> >>> not access since it is protected with authentication protocol.
> >>>  What this tripe DES encryption does is it makes it inaccessible. e.g. I
> >>> created one xml file and encrypted it with triple DES file and zipped it
> >>> and placed in one of my client's machine. When he tries to open the zip
> >> he
> >>> gets this message :
> >>> [image: Inline image 1]
> >>>
> >>> I'm looking for something similar that makes those DB files
> >> inaccessible in
> >>> client's machine.
> >>>
> >>>
> >>> Regards,
> >>> N.D.
> >>>
> >>> On Thu, Sep 25, 2014 at 5:54 PM, Dirk Kirsten <dk@basex.org> wrote:
> >>>
> >>>> I still don't really get it. Maybe it is just me, but I don't get the
> >>>> concept. ".NET Triple DES encryption" to me is just a standard
> >>>> encryption algorithm and does not describe any concept to me (I have no
> >>>> knowledge of .NET, but google didn't indicate otherwise).
> >>>>
> >>>> It seems like you don't want your users to directly access your XML
> >>>> documents, at least that is the point of encryption in your case I
> >>>> guess. But why do you not simply not give them access to the data? The
> >>>> user can't do anything with encrypted data, so it should be sufficient
> >>>> if the user simply has no access to the data.
> >>>>
> >>>> Encrypting them on the server seems not very beneficial to me. If you
> >>>> encrypt XML files, they will not be XML anymore, so you would have to
> >>>> store them as binary (hence, you couldn't use XQuery anymore to access
> >>>> the data directly, instead for each query you would have to decrypt the
> >>>> data, parse it and than you could query it).
> >>>>
> >>>> So if just your application should be able to access the XML documents,
> >>>> simply just give your application user credentials to access the
> >>>> documents on the server. What would be the point of your users being
> >>>> able to access the server, when they are unable to do anything with the
> >>>> encrypted data?!
> >>>>
> >>>> Cheers,
> >>>> Dirk
> >>>>
> >>>>
> >>>> On 25/09/14 14:12, Nilanjan Dutta wrote:
> >>>>> Not exactly.. Idea is to generate those Db files in server by feeding
> >> the
> >>>>> XML . And I'd zip the resulting database files and push it to the
> >> client
> >>>>> through wcf service.
> >>>>>
> >>>>> Here I want to encrypt these DB files in server and send and while
> >>>> reading
> >>>>> those DB files in the client I want to decrypt it programmatically.
> >> For
> >>>>> user, without running my application, it must remains encrypted. By
> >> doing
> >>>>> this, I want to prevent my users playing with those DB files by any
> >> mean.
> >>>>> Something similar to .NET Triple DES encryption.
> >>>>>
> >>>>> Regards,
> >>>>> N.D.
> >>>>>
> >>>>> On Thu, Sep 25, 2014 at 5:33 PM, Dirk Kirsten <dk@basex.org> wrote:
> >>>>>
> >>>>>> Hi Nilanjan,
> >>>>>>
> >>>>>> double praise for Marco is well-deserved - We always appreciate user
> >>>>>> feedback on the mailing list!
> >>>>>>
> >>>>>> I don't really get what you want to achieve with this kind of
> >>>>>> encryption. Do you want your user to be unable to modify the XML
> >>>>>> documents at your server? Then you could simply give them an account
> >>>>>> with read permissions only.
> >>>>>>
> >>>>>> Cheers,
> >>>>>> Dirk
> >>>>>>
> >>>>>> On 25/09/14 13:55, Nilanjan Dutta wrote:
> >>>>>>> My bad. I meant Marco and Dirk. Thanks once again  :)
> >>>>>>>
> >>>>>>> Regards,
> >>>>>>> N.D.
> >>>>>>>
> >>>>>>> On Thu, Sep 25, 2014 at 5:24 PM, Nilanjan Dutta <
> >>>>>>> nilanjan.dutta.india@gmail.com> wrote:
> >>>>>>>
> >>>>>>>> Thanks Marco and Marco for your prompt response.
> >>>>>>>> So that is OK now - I have to configure the client instance with a
> >> db
> >>>>>> path
> >>>>>>>> for those files and it should work.
> >>>>>>>> Now one more concern is, is there a way I can encrypt those files
> >>>> while
> >>>>>>>> pushing them to clients from the server? And decrypt in the client
> >>>>>> code? Or
> >>>>>>>> do I rely on some 3rd party tool to do that? I don't want my users
> >> to
> >>>>>> play
> >>>>>>>> around those files at all.
> >>>>>>>>
> >>>>>>>> Regards,
> >>>>>>>> N.D.
> >>>>>>>>
> >>>>>>>> On Thu, Sep 25, 2014 at 4:04 PM, Marco Lettere <
> >>>>>> marco.lettere@dedalus.eu>
> >>>>>>>> wrote:
> >>>>>>>>
> >>>>>>>>>  Hi Nilanjan,
> >>>>>>>>> I've done something similar and it works.
> >>>>>>>>> I even use rsync for synchronizing database directories calling it
> >>>> from
> >>>>>>>>> the xquery proc module.
> >>>>>>>>> Just it has to be done when no access to the data is occurring
> >>>> because
> >>>>>>>>> there could be consistency issues arising.
> >>>>>>>>> Regards,
> >>>>>>>>> M.
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> On 25/09/2014 12:16, Nilanjan Dutta wrote:
> >>>>>>>>>
> >>>>>>>>>  Hello Team,
> >>>>>>>>>
> >>>>>>>>>  In our project we are planning to use BaseX as XML DB.
> >>>>>>>>>
> >>>>>>>>>  My main concern is, we don't want to create DB again and again to
> >>>>>>>>> different machines with same XML file as input and would like to
> >>>> reuse
> >>>>>> the
> >>>>>>>>> DB that we'd generate in a server.
> >>>>>>>>>
> >>>>>>>>>  I see in the "data" directory of my BaseX installation these
> >> files
> >>>> are
> >>>>>>>>> generated when I create a DB by importing an XML:
> >>>>>>>>>
> >>>>>>>>>  [image: Inline image 1]
> >>>>>>>>>  Would like to know if these can be zipped and ported into
> >> different
> >>>>>>>>> machines and can be used to recreate the DB. Please do let me know
> >>>> how
> >>>>>> this
> >>>>>>>>> can be done .
> >>>>>>>>>
> >>>>>>>>>  Regards,
> >>>>>>>>> N
> >>>>>>>>> ​ ilanjan Dutta
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>
> >>>>>>>
> >>>>>>
> >>>>>> --
> >>>>>> Dirk Kirsten, BaseX GmbH, http://basex.org
> >>>>>> |-- Firmensitz: Blarerstrasse 56, 78462 Konstanz
> >>>>>> |-- Registergericht Freiburg, HRB: 708285, Geschäftsführer:
> >>>>>> |   Dr. Christian Grün, Dr. Alexander Holupirek, Michael Seiferle
> >>>>>> `-- Phone: 0049 7531 28 28 676, Fax: 0049 7531 20 05 22
> >>>>>>
> >>>>>
> >>>>
> >>>> --
> >>>> Dirk Kirsten, BaseX GmbH, http://basex.org
> >>>> |-- Firmensitz: Blarerstrasse 56, 78462 Konstanz
> >>>> |-- Registergericht Freiburg, HRB: 708285, Geschäftsführer:
> >>>> |   Dr. Christian Grün, Dr. Alexander Holupirek, Michael Seiferle
> >>>> `-- Phone: 0049 7531 28 28 676, Fax: 0049 7531 20 05 22
> >>>>
> >>>
> >>
> >> --
> >> Dirk Kirsten, BaseX GmbH, http://basex.org
> >> |-- Firmensitz: Blarerstrasse 56, 78462 Konstanz
> >> |-- Registergericht Freiburg, HRB: 708285, Geschäftsführer:
> >> |   Dr. Christian Grün, Dr. Alexander Holupirek, Michael Seiferle
> >> `-- Phone: 0049 7531 28 28 676, Fax: 0049 7531 20 05 22
> >>
> >
> >
>

--
Dirk Kirsten, BaseX GmbH, http://basex.org
|-- Firmensitz: Blarerstrasse 56, 78462 Konstanz
|-- Registergericht Freiburg, HRB: 708285, Geschäftsführer:
| Dr. Christian Grün, Dr. Alexander Holupirek, Michael Seiferle
`-- Phone: 0049 7531 28 28 676, Fax: 0049 7531 20 05 22