New SimpleCrypt page

[cincirin]

@Andre ... many, many apologies.
Indeed your algorithm works well, what induced me in error was CPUID opcode, which I compared with decrypted string. I was convinced that CPUID opcode with all features was always the same. But sometimes some bits are different (maybe cache information, I'll study in a few days)
Thanks anyway.

[andre]

[quote author="cincirin" date="1316417041"]@Andre ... many, many apologies.
Indeed your algorithm works well, what induced me in error was CPUID opcode, which I compared with decrypted string. I was convinced that CPUID opcode with all features was always the same. But sometimes some bits are different (maybe cache information, I'll study in a few days)
Thanks anyway.[/quote]

OK, glad to know that the issue is not in my code :-) Lots of luck in figuring out what is going wrong then!
One more note: you might want to think about getting a better key. 1316417041 is only a 32 bits number (0x4E76EE11). You might want to considder generating a real 64 bit key instead.

[andre]

[quote author="qxorm" date="1316359090"]Hi,

I read your article and it is very interesting !
[/quote]
Thanks for the compliment :-)

[quote]
I am the developer of QxOrm library (Object Relational Mapping for C++/Qt) and I would like to use your class to encrypt/decrypt some datas. Indeed, QxOrm library provides QxService module to create C++/Qt application server. Here is a tutorial if you want to see QxService module : http://www.qxorm.com/qxorm_en/tutorial_2.html
[/quote]
I am very interested in ORM myself (and database drivers and the likes), and I have looked at QxORM before. Very nice effort!
[quote]
So it would be great with an option to encrypt data before transfering it over network.

Can I use your class in QxOrm library ?
Can I add namespace for your class ?
Can I rename your class to add Qx prefix ?
I will not change anything else.
[/quote]
Would the above be doable based on the current licence of the code, or would you need the code under a different licence? I do not have objections to you including this code in QxOrm in principle, so I guess we can figure something out.

[qxorm]

I think it's ok for the licence : QxOrm library is under LGPL licence, so it seems compatible.

I just want (if possible) include your class into the namespace qx and rename it from SimpleCrypt to QxSimpleCrypt (like other classes into QxOrm library).

If I include your class into QxOrm library, I would like to set your name into the changes.txt file for the next version. Is it ok for you ?
Something like this :
New class qx::QxSimpleCrypt to provide encryption/decryption (thanks very much to Andre Somers) with QxService module : encrypt data before transfering it over network.

[andre]

Seems fine to me, as long as the copyright notice & licence in the source files remains in tact (and is observed), I have no objections to your modifications. The licence explicitly allows you to modify the code for your own use, after all.

Basically: I am fine with anybody using this code for any purpose, as long as:

• You don't pretend you wrote it yourself, and
• You don't make me responsible for your use of it or claim that I endorse it in some way.

Other than that: I hope you find it useful, and have lots of success with any application you use it in :-)

[qxorm]

Ok thanks, your SimpleCrypt class will be in the next version of QxOrm library ;-)

[andre]

Nice to know it is getting some use :-)

[qxorm]

QxOrm 1.1.9 just released with your SimpleCrypt class (renamed to qx::QxSimpleCrypt).
For more details : http://www.qxorm.com/qxorm_en/download.html
Thanks again ;o)

[saidiahd]

Hi Andre ,

a very nice work ,thanks

[mnosov]

Hi, Andre!

Thanks a lot for the article! I'd be glad to use this code in my project!

My question is also related to license. The project I'm working on is not an open-source. Is it ok if I copy/paste your code into my project (keeping copyright notice in source/header files)? Also my application doesn't have any 'About' page - is it OK that I'll not show to the end user your copyright notice (that you're the actual author of encryption)?

I have read your message above, my question is just for confirmation for my project

Thanks a lot in advance,
Michael

[andre]

Your application is bound to have some documentation or help system, right? I'd think there is enough opportunity to fullfil the licence terms that way. Licences do not get much more liberal than the one I have used...

[mnosov]

[quote author="Andre" date="1317372274"]Your application is bound to have some documentation or help system, right? I'd think there is enough opportunity to fullfil the licence terms that way. Licences do not get much more liberal than the one I have used...[/quote]
Ok, thanks, i'll add this notice to the global "copyright" file in the sources. I just needed confirmation that it is ok that this notice will not appear anywhere on the application's UI

[andre]

The relevant part of the licence states:
[quote]Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.[/quote]

So, if you are providing other materials/documentation with the binairy application, then you must basically repeat the licence block in that documentation or additional materials. That can also occur in in-application help or something like that. If you distribute your application as source, then you can place it there (basically: just keep the source file as-is - at least in terms of the licence header - and you are ok.)

[erwanage]

Hi,

First, Thanks for your work.
I'd like to use your class but i need some more help.
The constructor of SimpleCrypt only accept a quint64 as key.
But in my project, i have to convert a given passphrase (like "password") to this quint64 and cannot manage to do this.
You said in your topic "you can also use other means to get to a quint64 key, such as using some hash of a password and reducing that to 64 bits."
But i don't know how to do it.

Is there some easy way to do this?
Is there some existing class or wathever that do it?

regards.

[koahnig]

welcome to devnet

Did you see already "qHash":http://developer.qt.nokia.com/doc/qt-4.8/qhash.html#qHash-22 ?

[andre]

Well, the qHash function comes to mind, or perhaps you could use [[doc:QCryptographicHash]]. You add a bit a salt to your pass string, generate a hash, and combine the bits in the resulting hash to create a 64 bit value. If you use MD5, you get a 128bits hash. You could do something like this:

@
quint64 passToKey(const QString& password) {
QByteArray hash;
QCryptographicHash hasher(Md5);
hasher.addData(salt); //salt is a QByteArray with some random data
hasher.addData(password.toUtf8());
hash = hasher.result();

//we now have a QByteArray that is too long with a hash of the password.

//get the contents of the byte array into two quint64's. There are other ways...
quint64 part1, part2;
QBuffer buffer(hash);
QDataStream stream(&buffer);
stream >> part1 >> part2;
key = part1 ^ part2; //combine the two parts

return key;
}
@

Note: brain to editor, not tested.

Edit:
Note that qHash returns a 32 bits result, so you will have to combine two of these to get a 64 bits version. Perhaps using part of the password for hash1, and the other part for hash2, and then combining the result to get a 64 bits key.

[erwanage]

Thanks for your help.
I'm not at ease with with hashing and combining stuff :/
How can you do that?
How do you combine 2 unsigned int?

[andre]

In the same way I do in the snippet I posted, for instance. I use bitshifting, but that is the same as multiplication by 2-to-the-power-of-n. Basically, what you do is:

put the values of your ints in 64 bits variables

shift one of the values 32 bits by either:

multiplying by 0xFFFFFFFF, or

bitshifting

add the two numbers by either:

simply adding the numbers, or

using a binary OR operation like I did in my sample.

[rich]

Just a note that this appears to be a Vigenere cipher scheme (see http://en.wikipedia.org/wiki/Vigenère_cipher for details) if you simply want basic scrambling of data to prevent trivial access to the plain text then this could well be sufficient, but it's not very strong. Particularly be careful of using this for long texts.

[andre]

Thanks for the note. If I understand the page you link, I'm not sure that the class implements what qualifies as a Vigenere cipher, but I will agree that it does not provide strong cryptography.

The small additional trick is that the code uses the value of the previous code block as part of the key for the next block. That will hinder the kinds of analysis described in the article, if I understand it correctly. The key length is known in this case: 8 bytes, but because the key is mixed with the previously generated cypher text, it does not work to just decrypt the text as eight different cesar cyphers.