Decrypt AES with OpenSSL & Qt 5.5.1 Win32 VS2013

qDebug

I'm doing something wrong and i can't figure out what. Changed to utf8, plain key and iv, vise versa, but somehow i won't get this example decrypted. It does work this way in the openssl command line tool.

So far i did not find any example code that used a custom key and iv, only random generated ones. Also gave QCA::SymmetricKey::SymmetricKey(key) and QCA::InitializationVector::InitializationVector(iv) a chance, did not really help.

Any ideas?

SGaist

Your code doesn't match all the openssl line options. -a -A means that you must first decode your Base64 encoded string.

qDebug

@SGaist Thanks! I don't know why but i did forget about the base64 decode. After changing from toLatin1 to toUtf8 and decode the base64 string i don't get the final error anymore. But i won't get the expected plain text only

o????:??????a?s?]??Iy?[W6???l??(f?$?I{??^ ????Cï5?

same result if i use

qDebug() << "process: " << QCA::SecureArray(cipher.process(decodedBase64.toUtf8())).data();

Maybe the utf8 conversion is the problem but it won't take a QString. I get the same result if i append the string to a QByteArray. Btw. noting changes if i use QByteArray to decode base64 or QCA::Base64 decoder(QCA::Decode);

At least the final error is gone, that's some progress! ;)

Edit: And i added "md5" as crypto service provider because it was encoded this way. md5 is in the list of providers, so i hope i implemented this correctly.

QCA::Cipher cipher(QString("aes128"), QCA::Cipher::CBC, QCA::Cipher::NoPadding, QCA::Decode, key, iv, "md5");

But cipher.provider()->name(); returns "qca-ossl".

SGaist

Do you mean that you passed your original string through md5 before encrypting it ?

qDebug

The password / key was md5 hashed.

key = md5(utf8(password));

and the iv are the first 16 bytes from the base64 string.

Edit: Not the key of course, the iv are the first 16 bytes from the base64 string.

SGaist

Can you show the complete procedure ?

qDebug

Thanks for asking. This is the VB code to encrypt the string:

Dim AES As New RijndaelManaged

Dim md5 As New MD5CryptoServiceProvider
Dim key() As Byte = md5.ComputeHash(Encoding.UTF8.GetBytes(password))

md5.Clear()
AES.Key = key
AES.GenerateIV()
Dim iv() As Byte = AES.IV
Dim ms As New MemoryStream

ms.Write(iv, 0, iv.Length)

Dim cs As New CryptoStream(ms, AES.CreateEncryptor, CryptoStreamMode.Write)
Dim data() As Byte = System.Text.Encoding.UTF8.GetBytes(string)

cs.Write(data, 0, data.Length)
cs.FlushFinalBlock()

Dim encoded() As Byte = ms.ToArray()
Return (Convert.ToBase64String(encoded))
cs.Close()
AES.Clear()

As far as i can tell is the password and the string are utf8 bytes and the password is the md5 hash of it. I did try to pass it through

QCA::SecureArray key = QCA::SecureArray::SecureArray(password);

before and after utf8 and md5. So far no luck.

Thank you!

qDebug

And this is my attempt:

QString MainWindow::decryptString(QString password, QString encodedString)
{
    // final decodec string
    QString decodedString;

    // get the iv
    QByteArray array(encodedString.left(16).toStdString().c_str(), encodedString.left(16).size());
    QCA::SecureArray iv = array.toHex();

    // decode base64
    QCA::Base64 decoder(QCA::Decode);
    const char* decoded = decoder.decodeString(encodedString).toStdString().c_str();

    QCA::SecureArray key = QByteArray(QCryptographicHash::hash(password.toUtf8(), QCryptographicHash::Md5).toHex());
    QCA::SecureArray arg = decoded;

    QCA::Cipher cipher(QString("aes128"), QCA::Cipher::CBC, QCA::Cipher::NoPadding, QCA::Decode, key, iv);
    QCA::SecureArray plainText = cipher.update(arg);

    if(!cipher.ok())
    {
        qDebug() << "update Fail";
    }

    cipher.final();
    if(!cipher.ok())
    {
        qDebug() << "final fail";
    }

    qDebug() << "process: " << QCA::SecureArray(cipher.process(decoded)).data();

    decodedString = plainText.data();
    qDebug() << "Decoded: " << decodedString;

    return decodedString;
}

I call it like:

qDebug() << "decoded: " << decryptString("test", "PpUr+LMHvaKmf0q6J7Oyzo4jbFO5kfWyXl0d8nD3hyM=");

The only step i masted was getting rid of the final fail, but i don't know if that was really the case. Not sure how, i changed this so often, i don't even know how much time i spend on this. I didn't think it can be that difficult to use it.

So far i still did not fine one single example code using qca with aes128cbc and custom iv and key. Very, very strange.

Any ideas?

Thanks!

SGaist

Do you mean this example ?

qDebug

Yes. It is the only one i found so far. But the iv and key are random generated, it does not show how to use an already existing key and iv correctly. I really don't know what i am missing here.

SGaist

Just replace the random key and iv by yours.

qDebug

I did. That was my first idea, did not work. Id did check the key and iv output, same as i use with openssl, does work in openssl, does not work in Qt / QCA - at least not the way i do it. I don't know, maybe i miss something in general or just just a tiny mistake, but after days and hours, i can confirm, it won't work for me.

SGaist

I took the example as is, replaced key and iv by

QByteArray key("098f6bcd4621d373cade4e832627b4f6");
QByteArray iv("d8e8fca2dc0f896fd7cb4cb0031ba249");

and it's working fine.

qDebug

If you can tell me why this code

QString decodedString;
QCA::Initializer init;
QByteArray array(encodedString.left(16).toStdString().c_str(), encodedString.left(16).size());
QCA::SecureArray iv = array.toHex();
QCA::Base64 decoder(QCA::Decode);
QCA::SecureArray decoded = decoder.decodeString(encodedString).toStdString().c_str();
QCA::SecureArray key = QByteArray(QCryptographicHash::hash(password.toUtf8(), QCryptographicHash::Md5).toHex());
QCA::Cipher cipher(QString("aes128"), QCA::Cipher::CBC, QCA::Cipher::NoPadding, QCA::Decode, key, iv);
QCA::SecureArray plainText = cipher.update(decoded);
if(!cipher.ok())
{
	qDebug() << "update Fail";
}
plainText  = cipher.final();
if(!cipher.ok())
{
	qDebug() << "final fail";
}
qDebug() << "process: " << QCA::SecureArray(cipher.process(decoded)).data();
QString decodedString = plainText.data();
qDebug() << "Decoded: " << decodedString;

is not working, it may help me. If you tell me some code is working for you, it does not. This is btw. taken from the example, i did not change anything beside adding key and iv.

SGaist

The first thing that looks strange is your iv creation. You take 16 bytes of your encoded string and turn it to hexadecimal. Why ?

Also, why all the conversions ? Just use QByteArray.

qDebug

098f6bcd4621d373cade4e832627b4f6 is "test" in md5. all the strings i have to decode are encoded with a different iv, the iv is always the first 16 bytes in hex from the encoded string, d8e8fca2dc0f896fd7cb4cb0031ba249 in this case.

So i have to hash the key "test" and get the iv from the encoded string.

And of course, i did test the key and iv just as QByteArray, before and after you posted the example, but the decoding so far did always fail.

SGaist

That's something that is really not clear. You are telling me that you are using as iv for the decoding a part of the alrey encoded string ? So what did you use as iv for the encoding part ?

qDebug

The iv is taken from the still encrypted and base64 encoded string, first 16 bytes hex. iv 507055722b4c4d4876614b6d66307136 is QByteArray array(encodedString.left(16).toStdString().c_str(), encodedString.left(16).size()); qDebug() << "iv: " << array.toHex();

Proof:

echo PpUr+LMHvaKmf0q6J7Oyzo4jbFO5kfWyXl0d8nD3hyM= | openssl enc -d -a -A -aes-128-cbc -iv 507055722b4c4d4876614b6d66307136 -K 098f6bcd4621d373cade4e832627b4f6
8°&¦=YaÌ?{Äa+Dr. Test

SGaist

And what iv did you use to encrypt the string ?

qDebug

If you scroll up a few posts, there is the source code.