New SimpleCrypt page

[andre]

I have just added a "page":http://developer.qt.nokia.com/wiki/Simple_encryption in the Snippets category that details a class to deal with some simple encryption and decryption. I would really welcome any comments you may have, on the text of the Wiki page, the API of the class, or the strength of the encryption algorithm used. Note that I am not an expert in cryptography :-)

Would it be useful to add a section discussing the actual algorithm used in the class?

[ZapB]

Hi Andre,

nice entry. Thanks for sharing the code.

[Alicemirror]

Andre, I think it's useful.

This kind of cipher as you explain seems simple and efficient, just what a lot of mobile developers needs to give to their applications the option for data to be "unreadable by others".

I am thinking to those that I am developing: "naijanimi":projects.forum.nokia.com/naijanimi (at projects.forum.nokia.com/naijanimi; restricted access) It is at an early stage but I should (to be clear: I SHOULD ;) ) go ahead very fast this next w.e. The encryption capability, not really required by the customer, is missing but needed: it is an application to send free SMS and some data (just user and login, phone number etc) are saved on the phone and if they are encrypted it is best.

Edit: make link into real link, and added note on restricted access to page; Andre

[andre]

I am glad people seem to appreciate the snippets I have posted so far.

[quote author="Andre" date="1300457411"]Would it be useful to add a section discussing the actual algorithm used in the class?[/quote]

Does anyone think it is -possible- nessecairy to document this in more detail in the article?

[Alicemirror]

Hi Andre, I can if you explain to me a bit more what do yo have in mind. What I am thinking is to use this class in an application that I am building in these days, so the reference code can became a set of snippets for users that want to use, while the application itself can be a usage sample (it is shared on projects.forum.nokia.com/najianimi). The informations can be collected in the wiki integrating the page you have already wrote.

[andre]

I'm not sure the page needs a lot of snippets illustrating the use. It seems quite clear to me. Or do you think it needs more examples?

[Alicemirror]

Andre, I was no clear in my thought. The page is clear, as is, with the snippet. I agree that a wiki page with too much code became confusing. What I mean is that integrating your page, with a little more documentation about encryption and a project that can be an example (that use in a precise vode source your class) can be useful.

Usually what I find in documentation on the net regarding encryption or similar, is too much code or too much teory.

[saidiahd]

thank you Andre , a very good work

[Alicemirror]

Sure ! :) It's a great starting point.

[milot.shala]

Nice entry Andre.

[andre]

I am currently working on a version 2, with these added features:

• optional integrity checks using a checksum or a cryptographic hash
• error reporting
• slightly higher security due to added random character. That should make it harder to guess the first byte of the key based on the fact that there are only a limited number of characters used normally. Should increase effective key length by an guestimated 3 bits.

[andre]

I have just uploaded a modified version that implements the above features.

[Alicemirror]

I am waiting in the shade... When I start (hope tomorrow) I can get the last version :)

[goetz]

If you miss the documentation tools discussion: I've split it out to a "new thread":http://developer.qt.nokia.com/forums/viewthread/4619/

[andre]

I have added a "separate page":http://developer.qt.nokia.com/wiki/SimpleCrypt_algorithm_details that details the algorithm and the layout of the cypher text. Of course, I also added a link from the main page.

[paucoma]

Hi Andre,
First: Thanks for sharing the code.

Second: You've got some typos in the Example usage code.

• Name of the Class: SimpleCypt --> SimpleCrypt
• crypto.setCompression(SimpleCrypto::CompressionAlways)
  ** crypto.setCompressionMode(SimpleCrypt::CompressionAlways);
• crypto.setIntegrityProtection(SimpleCrypto::ProtectHash);
  ** crypto.setIntegrityProtectionMode(SimpleCrypt::ProtectionHash);
• SimpleCrypt.ErrorNoError --> SimpleCrypt::ErrorNoError

Third:
The String Encryption and Decryption works fine, but for the binary version I seem to be having some difficulties.

my main.cpp
@
#include "simplecrypt.h"

#include <QString>
#include <QDebug>
#include <QBuffer>
#include <QDataStream>

int main(){
QString txStr = "Hello world!";

SimpleCrypt crypto(Q_UINT64_C(0x7F29B208)); //some random number
// crypto.setCompressionMode(SimpleCrypt::CompressionAlways);
// crypto.setIntegrityProtectionMode(SimpleCrypt::ProtectionHash);
QBuffer txB;
QDataStream s(&txB);
s << txStr;

QByteArray cypherBytes = crypto.encryptToByteArray(txB.data());
if (crypto.lastError() == SimpleCrypt::ErrorNoError) {
qDebug() << cypherBytes;
}

SimpleCrypt cryptu(Q_UINT64_C(0x7F29B208)); //some random number
QByteArray plainBytes = cryptu.decryptToByteArray(cypherBytes);
if (!cryptu.lastError() == SimpleCrypt::ErrorNoError) {
qDebug() << "decrypt error";
return 0;
}
qDebug() << plainBytes;

QString rxStr;
QBuffer rxB(&plainBytes);
QDataStream rs(&rxB);
rs >> rxStr;
qDebug() << rxStr;
return 0;
}
@

My Output (console):

"??Sß+"
""
""

What have I missed or using incorrectly?

Thanks again for the contribution.

[paucoma]

So I've played a bit around I've come to the conclusion that I'm using QDataStream incorrectly.

My Test Code: main.cpp
@
#include <QString>
#include <QDebug>
#include <QBuffer>
#include <QDataStream>
int main(){
QString txStr = "Hello world!";
QString rxStr;

QBuffer txB;
txB.open(QIODevice::ReadWrite);
QDataStream s(&txB);
qDebug() << txB.size();
s << txStr;
qDebug() << txB.size();
s >> rxStr;
qDebug() << rxStr;
return 0;
}
@

My Output:
0
28
""

So the buffer is being filled but not correctly being read out.. why not?

[giesbert]

That's an easy question. Your problem is the stream position:

you write to the stream, then start reading after the written bytes :-)

try out the following:

@
#include <QString>
#include <QDebug>
#include <QBuffer>
#include <QDataStream>
int main()
{
QString txStr = "Hello world!";
QString rxStr;

QBuffer txB;
txB.open(QIODevice::WriteOnly);
QDataStream s(&txB);
qDebug() << txB.size();
s << txStr;
qDebug() << txB.size();
txB.close(); // sets stream position to 0 !!!

txB.open(QIODevice::ReadOnly);
QDataStream s2(&txB);
s2 >> rxStr;
qDebug() << rxStr;
return 0;

}
@

or use a seek in between

@
#include <QString>
#include <QDebug>
#include <QBuffer>
#include <QDataStream>
int main()
{
QString txStr = "Hello world!";
QString rxStr;

QBuffer txB;
txB.open(QIODevice::WriteOnly);
QDataStream s(&txB);
qDebug() << txB.size();
s << txStr;
qDebug() << txB.size();
txB.seek(0); // sets stream position to 0 !!!
s >> rxStr;
qDebug() << rxStr;
return 0;

}
@

I did not compile the code, so it might contain typos

[paucoma]

Aha, got it all sorted out, thanks

I had my suspicions on that, but thought that the "<<" and ">>" operators may use seperate index variables.

Andre: it would be great if you could incorporate in the Example usage code the following so it works out of the box.

@
buffer.open(QIODevice::WriteOnly);
buffer.close();
buffer.open(QIODevice::ReadOnly);
@

Because newbies like myself:

• copy + paste + compile
  ** if it works -> adapt to needs
  ** if it doesn't -> get lost in the simplest things

Although I must admit that I am learning loads of things through all these problems I get myself into.

Gerolf: Once again thanks for your quick and effective response.

[andre]

paucoma, thank you for your comments and suggestions. I have changed the wiki page accordingly. I am glad you solved the problem, and that it turned out the class itself was not at fault ;-)

I must admit that I wrote the examples directly in the wiki page, and thats when errors like these happen. Sorry about that! I hope the current version is more managable? Note that I was talking about "at the other end", implying that the decryption code was not meant to be used in the same function (and thus, implicitly, with the same buffer).