New SimpleCrypt page

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).

paucoma

Thanks Andre for making the modifications.

I have corrected myself a few other details I found.

P.S. I didn't know that I had such a priviledge.

andre

Thanks for your effort, I really appreciate it. If you want, you're welcome to update it yourself in the wiki article :-)

giesbert

Hi Andre,

one suggestion to the wiki page:
In the section SimpleCrypt in use it would be nice to have a list of the encryp/decrypt functions. You state thete are two times 4, but not the names :-)
this means searching inside the code :-)

The rest sound really god. Thanks for the article.

andre

[quote author="Gerolf" date="1300958192"]Hi Andre,

one suggestion to the wiki page:
In the section SimpleCrypt in use it would be nice to have a list of the encryp/decrypt functions. You state thete are two times 4, but not the names :-)
this means searching inside the code :-)

The rest sound really god. Thanks for the article.[/quote]

Fair enough, done. :-)

Thanks for the praise.

giesbert

Hi Andre,

I'm currently reading your second article, and found the following "here":http://developer.qt.nokia.com/wiki/SimpleCrypt_algorithm_details#00f4e5788aab6d3546bb433842dbbefc :

bq. The payload data block’s contents are encrypted with a four byte (quint64) key.

quint64 is a 64 bit integer, which means 8 byte.

so also in the snipet page, you say:

@
SimpleCrypt crypto(Q_UINT64_C(0x7F29B208)); //some random number
@

this is just a 32 bit number, not 64 bit.

@
void SimpleCrypt::splitKey()
{
m_keyParts.clear();
m_keyParts.resize(4);
for (int i=0;i<4;i++) {
quint64 part = m_key;
for (int j=i; j>0; j--)
part = part >> 8;
part = part & 0xff;
m_keyParts[i] = static_cast<char>(part);
}
}
@

this also only uses 4 bytes, not 8.

giesbert

some additional topics:

in "Decrypted payload":http://developer.qt.nokia.com/wiki/SimpleCrypt_algorithm_details#2d478ba9ee3cf03e338b506b1a0292dc

SH1 and CRC have the same description:

bq. In case the Protection Checksum flag has been set, the layout of the decrypted payload looks like this:

I think this is just a copy paste error.

As I'm through now, no more things :-)
Very good article, interesting to read. Thanks.

andre

Thank you very much for this catch, Gerolf! You are absolutely right, and this is a big mistake in the algorithm as well. I will take care of fixing this ASAP.

andre

OK, fixed on both pages. Very embarrassing, I must say. :(

giesbert

Now it looks good, thanks :-)