New SimpleCrypt page
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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 partsreturn 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. -
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.
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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.
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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.
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Great job, easy to use. One question, I tested my app on Debian and Mint and no problem, but on Fedora 17 and Arch
I get "Invalid version or not a cyphertext."@ QByteArray ba = cypher;
char version = ba.at(0); if (version !=3) { //we only work with version 3 m_lastError = ErrorUnknownVersion; qWarning() << "Invalid version or not a cyphertext."; return QByteArray(); }@ -
Hi,
[quote author="Andre" date="1300457411"]I have just added a "page":http://developer.qt.nokia.com/wiki/Simple_encryption in the Snippets category [/quote]
Thanks for this class. I am invoking it's constructor with my predefined key (my secret) and I am wondering why qsrand() is initialized with currentTimeMillis or similar (in the constructor code)? I don't get the same encryption results on multiple invocations so I used my quint64 key to initialize qsrand (in the constructor), then it works..
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SimpleCrypt c1(Q_UINT64_C(0x0c2ad4a4acb9f023)); //some random number
SimpleCrypt c2(Q_UINT64_C(0x0c2ad4a4acb9f023)); //some random numberqDebug() << "Crypt1 " << c1.encryptToString(QString("justatest"));
qDebug() << "Crypt2 " << c2.encryptToString(QString("justatest"));
@Output
@
Crypt1 "AwLLXV+ZSO+x3Ise1Aw="
Crypt2 "AwIUgoBGlzBuA1TBC9M="
@Just wondering :)
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Why would you want to have the same cypher text when using the same clear text and key? As long as the decrypted plain text from these cypher texts is the same, what is the problem with having different cypher texts? The algorithm uses a randomization of the string on purpose. It makes it much harder to leak part of the key because analysis is much harder this way.
An explanation is in the "details page":/wiki/SimpleCrypt_algorithm_details#2d478ba9ee3cf03e338b506b1a0292dc that has more on the idea of using a random number as a leading byte.
You replacing that they way you did partly negates this, and thus makes the cypher weaker by a couple of bits. Note that even with your change, encrypting the same plain text using the same SimpleCrypt instance twice will result in different cypher texts.
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Hi Andre,
Thanks for answering; I wasn't looking for reasonably strong encryption - I just wanted to always get the same encrypted string for the same input (private key+string_to_be_encrypted); its just for private use anyway, and non-critical.
I am using QCryptographicHash for that now, it solves my problem
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[quote author="Andre" date="1356878054"]Eh, no, that class does not solve your problem, if you are indeed looking for encryption rather than hashing. There is a big difference between the two... [/quote]
That's a chicken and egg problem: I don't want to elaborate on "my problem" and hence prove that I am fine with hashing because of concerns of privacy. Please understand that and thank you for your help.
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good thing I changed was this:
@//QString cypherString = QString::fromAscii(cypher.toBase64());
QString cypherString = QString::fromUtf8(cypher.toBase64());//QString cypherString = QString::fromAscii(cypher.toBase64());
QString cypherString = QString::fromUtf8(cypher.toBase64());//QByteArray cyphertextArray = QByteArray::fromBase64(cyphertext.toAscii());
QByteArray cyphertextArray = QByteArray::fromBase64(cyphertext.toUtf8());//QByteArray cyphertextArray = QByteArray::fromBase64(cyphertext.toAscii());
QByteArray cyphertextArray = QByteArray::fromBase64(cyphertext.toUtf8());@there will be well done this.
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I was getting SIGABRT's when attempting to decrypt an empty string with a Qt with debugging enabled. So I've added a little check. Doesn't seem possible to link to wiki history diffs, but you can see it there.