Decrypt AES with OpenSSL & Qt 5.5.1 Win32 VS2013

qDebug

Hello!

Did hit a dead end trying to decode a AES encoded string using Openssl 1.0.1s and Qt 5.5.1 Win32 Visual Studio 2013. Since it works on the commandline with openssl.exe it has to be my code or implementation. I'm using Qt Creator 3.5.1.

After compiling Openssl (shared libs + debug) i just added

win32: LIBS += -L$$PWD/openssl/lib/ -llibeay32
INCLUDEPATH += $$PWD/openssl/include
DEPENDPATH += $$PWD/openssl/include

to my .pro file, run qmake and did build all and run the app. But so far only crashes without any error.

Here is my code:

#include <openssl/conf.h>
#include <openssl/evp.h>
#include <openssl/err.h>

// password: test
// cypertext: Dr. Test
// works: PpUr+LMHvaKmf0q6J7Oyzo4jbFO5kfWyXl0d8nD3hyM= | openssl enc -d -a -A -aes-128-cbc -iv 507055722b4c4d4876614b6d66307136-K 098f6bcd4621d373cade4e832627b4f6

QString cypher = "PpUr+LMHvaKmf0q6J7Oyzo4jbFO5kfWyXl0d8nD3hyM=";
QString pw_md5 = "098f6bcd4621d373cade4e832627b4f6";
QString iv16 = "507055722b4c4d4876614b6d66307136";

ERR_load_crypto_strings();
OpenSSL_add_all_algorithms();
OPENSSL_config(NULL);

unsigned char *ciphertext = (unsigned char*) cypher.data();
int ciphertext_len = static_cast< int >(cypher.size());
unsigned char *key = (unsigned char*) pw_md5.data();
unsigned char *iv = (unsigned char*) iv16.data();
unsigned char *plaintext = (unsigned char*) "";

qDebug() << "ciphertext: " << ciphertext;
qDebug() << "ciphertext_len: " << ciphertext_len;

EVP_CIPHER_CTX *ctx;

int len;
int plaintext_len;

if(!(ctx = EVP_CIPHER_CTX_new()))
{
	ERR_print_errors_fp(stderr);
}

if(1 != EVP_DecryptInit_ex(ctx, EVP_aes_128_cbc(), NULL, key, iv))
{
	ERR_print_errors_fp(stderr);
}

if(1 != EVP_DecryptUpdate(ctx, plaintext, &len, ciphertext, ciphertext_len))
{
	ERR_print_errors_fp(stderr);
}
plaintext_len = len;

if(1 != EVP_DecryptFinal_ex(ctx, plaintext + len, &len))
{
	ERR_print_errors_fp(stderr);
}
plaintext_len += len;

EVP_CIPHER_CTX_free(ctx);
EVP_cleanup();
ERR_free_strings();

qDebug() << "plaintext_len: " << plaintext_len;
qDebug() << "plaintext: " << plaintext;

if i set

int ciphertext_len = 0;

i get at least a final block length error (after i quit the app) and the app won't crash. If i set it to 44 manually, the app still crashes.

Any ideas?

Thanks!

hskoglund

Hi, don't know about the OpenSSL block lengths problem, but the reason you're crashing I think is because you're allocating memory badly, for example
unsigned char *plaintext = (unsigned char*) ""; is almost always guaranteed to crash.
Why not skip the QStrings, do something simpler like this:

...
unsigned char cypher[] = "PpUr+LMHvaKmf0q6J7Oyzo4jbFO5kfWyXl0d8nD3hyM=";
unsigned char pw_md5[] = "098f6bcd4621d373cade4e832627b4f6";
unsigned char iv16[] = "d8e8fca2dc0f896fd7cb4cb0031ba249";

ERR_load_crypto_strings();
OpenSSL_add_all_algorithms();
OPENSSL_config(NULL);

unsigned char *ciphertext = cypher;
int ciphertext_len = sizeof(cypher) - 1;
unsigned char *key = pw_md5;
unsigned char *iv = iv16;
unsigned char plaintext[1024];
...

Now the app shouldn't crash, so you can try debugging the OpenSSL decrypting stuff...

qDebug

Thanks to you, no more crashing. :D

Tank you!

Still getting wrong last black error. But at least i can try to fix that somehow. I was guessing some Qt users may use Openssl and got experience using it with Qt.

SGaist

Hi,

Depending on your needs the QCA module might be something to look into.

qDebug

@SGaist Thanks, but it is no option for me. Did load qca-2.1.0 and also did try to compile it on Windows VS2013 and cmake. No chance i will get this running without a step my step tutorial for Win. I did try to compile it on Ubuntu, no problem, works instantly, Windows, nah. I will look into this module again if i ever reach a level called ultra skilled hacker.

Also tryed Crypto++ and was able to get some code running, but the sample codes do not work for me and the docs are not really helpful.

SGaist

To avoid the need to level-up that high: open the QCA project in Qt Creator and build it with the Kit you are using for your project, then install it and you should be done. IIRC, you can even choose the install target from the list in the Project panel.

qDebug

Thank you!

But no luck, it won't compile. 5 errors.

C2061: syntax error : identifier 'QIODevice'
C2065: 'QIODevice' : undeclared identifier
C2065: 'file' : undeclared identifier
C2448: 'QCA::Hash::update' : function-style initializer appears to be a function definition
C2061: syntax error : identifier 'QIODevice'

SGaist

Where did you get QCA from ?

qDebug

@SGaist Thank you for asking. I got it from http://delta.affinix.com/qca/ (qca-2.1.0.tar.gz).

Edit: Did find a newer version @ https://www.freshports.org/devel/qca-qt5/ (qca-2.1.1.tar.xz) and i was able to compile it. At least the debug files did compile. But the big problem is

if(!QCA::isSupported("aes128"))
{
     qDebug() << "No AES 128 supported ...";
}
if(!QCA::isSupported("aes128-cbc"))
{
     qDebug() << "No AES 128  CBC supported ...";
}
if(!QCA::isSupported("aes128-cbc-pkcs7"))
{
     qDebug() << "No AES 128 CBS pkcs7 supported ...";
}

According to the docs http://delta.affinix.com/docs/qca/ my version does not support AES CBC at all so it is worthless to me atm. Did i something wrong here?

win32: LIBS += -L$$PWD/qca/lib/ -lqca-qt5d
INCLUDEPATH += $$PWD/qca/include
DEPENDPATH += $$PWD/qca/include

and

#include <QtCrypto/QtCrypto>

Thanks!

SGaist

CBS ? Don't you mean CBC ? If CBC, then yes it does, just take a look at QCA's code.

Before calling these function did you initialize QCA ?

Also, do you have OpenSSL in your PATH environment variable when running the application ?

qDebug

Yes, CBC, sorry.

I did put a QCA::Initializer init; after ui->setupUi(this); And yes, Openssl is in my paths env (C:\OpenSSL-Win32\bin), i can call openssl.exe from command line.

cmake tells me:

qca-botan off
qca-cyrus-sasl off
qca-gcrypt off
qca-gnupg on
qca-logger on
qca-nss off
qca-ossl on
qca-pkcs11 off
qca-softstore on

Do you know if i need one or more plugins to use AES 128 CBC?

qDebug

I've mastered the installation now. After building it with Qt Creator i went to the build directory and executed a nmake install. After editing the include paths i also had to add CONFIG += crypto in my pro file. So far no more AES128 CBC not supported errors. But still no luck in decrypting my string.

QString ciphertext = "PpUr+LMHvaKmf0q6J7Oyzo4jbFO5kfWyXl0d8nD3hyM=";
QString key1 = "098f6bcd4621d373cade4e832627b4f6";
QString iv1 = "507055722b4c4d4876614b6d66307136";

QByteArray key;
key = key1.toLatin1();

QByteArray iv;
iv = iv1.toLatin1();

QCA::SecureArray arg = ciphertext.toLatin1();
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";
}
plainText = cipher.final();
if(!cipher.ok())
{
	qDebug() << "final fail";
}

qDebug() << "plainText.data(): " << plainText.data();

The decrypted text should be Dr. Test and password is test. The iv are the fist 16 bytes from the ciphertext and the password is a md5 hash from test. Works in openssl command line. I get a qDebug final fail result.

Any ideas about that?

Thanks!

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!

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