aes-cmac.cpp

This example shows how to implement a client side "provider".There are three important parts to this:

• the class derived from QCA::Provider (in this example called "ClientSideProvider"), that generates the context class
• one or more context classes (in this example only one, implementing AES-CMAC, called "AESCMACContext")
• a call to QCA::insertProvider, to add the QCA::Provider subclass into QCA

/*
 Copyright (C) 2006 Brad Hards <bradh@frogmouth.net>

 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
 in the Software without restriction, including without limitation the rights
 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 copies of the Software, and to permit persons to whom the Software is
 furnished to do so, subject to the following conditions:

 The above copyright notice and this permission notice shall be included in
 all copies or substantial portions of the Software.

 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
 AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
 AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

// QtCrypto has the declarations for all of QCA
#include <QtCrypto>

#include <QCoreApplication>
#include <QDebug>

#ifdef QT_STATICPLUGIN
#include "import_plugins.h"
#endif

class AESCMACContext : public QCA::MACContext
{
    Q_OBJECT
public:
    AESCMACContext(QCA::Provider *p) : QCA::MACContext(p, QStringLiteral("cmac(aes)"))
    {
    }

    // Helper to left shift an arbitrary length array
    // This is heavily based on the example in the I-D.
    QCA::SecureArray leftShift(const QCA::SecureArray &array)
    {
        // We create an output of the same size as the input
        QCA::SecureArray out(array.size());
        // We handle one byte at a time - this is the high bit
        // from the previous byte.
        int overflow = 0;

        // work through each byte.
        for (int i = array.size() -1; i >= 0; --i) {
            // do the left shift on this byte.
            out[i] = array[i] << 1;
            // make the low bit on this byte be the high bit
            // from the previous byte.
            out[i] |= overflow;
            // save the high bit for next time
            overflow = (array[i] & 0x80) ? 1 : 0;
        }
        return out;
    }


    // Helper to XOR two arrays - must be same length
    QCA::SecureArray xorArray(const QCA::SecureArray &array1,
                          const QCA::SecureArray &array2)
    {
        if (array1.size() != array2.size())
            // empty array
            return QCA::SecureArray();

        QCA::SecureArray result(array1.size());

        for (int i = 0; i < array1.size(); ++i)
            result[i] = array1[i] ^ array2[i];

        return result;
    }


    void setup(const QCA::SymmetricKey &key) override
    {
        // We might not have a real key, since this can get called
        // from the constructor.
        if (key.size() == 0)
            return;

        m_key = key;
        // Generate the subkeys
        QCA::SecureArray const_Zero(16);
        QCA::SecureArray const_Rb(16);
        const_Rb[15] = (char)0x87;

        m_X = const_Zero;
        m_residual = QCA::SecureArray();

        // Figure 2.2, step 1.
        QCA::Cipher aesObj(QStringLiteral("aes128"),
                           QCA::Cipher::ECB, QCA::Cipher::DefaultPadding,
                           QCA::Encode, key);
        QCA::SecureArray L = aesObj.process(const_Zero);

        // Figure 2.2, step 2
        if (0 == (L[0] & 0x80))
            m_k1 = leftShift(L);
        else
            m_k1 = xorArray(leftShift(L), const_Rb);

        // Figure 2.2, step 3
        if (0 == (m_k1[0] & 0x80))
            m_k2 = leftShift(m_k1);
        else
            m_k2 = xorArray(leftShift(m_k1), const_Rb);
    }

    QCA::Provider::Context *clone() const override
    {
        return new AESCMACContext(*this);
    }

    void clear() 
    {
        setup(m_key);
    }

    QCA::KeyLength keyLength() const override
    {
        return QCA::KeyLength(16, 16, 1);
    }

    // This is a bit different to the way the I-D does it,
    // to allow for multiple update() calls.
    void update(const QCA::MemoryRegion &a) override
    {
        QCA::SecureArray bytesToProcess = m_residual + a;
        int blockNum;
        // note that we don't want to do the last full block here, because
        // it needs special treatment in final().
        for (blockNum = 0; blockNum < ((bytesToProcess.size()-1)/16); ++blockNum) {
            // copy a block of data
            QCA::SecureArray thisBlock(16);
            for (int yalv = 0; yalv < 16; ++yalv)
                thisBlock[yalv] = bytesToProcess[blockNum*16 + yalv];

            m_Y = xorArray(m_X, thisBlock);

            QCA::Cipher aesObj(QStringLiteral("aes128"),
                               QCA::Cipher::ECB, QCA::Cipher::DefaultPadding,
                               QCA::Encode, m_key);
            m_X = aesObj.process(m_Y);
        }
        // This can be between 1 and 16
        int numBytesLeft = bytesToProcess.size() - 16*blockNum;
        // we copy the left over part
        m_residual.resize(numBytesLeft);
        for(int yalv = 0; yalv < numBytesLeft; ++yalv)
            m_residual[yalv] = bytesToProcess[blockNum*16 + yalv];
    }

    void final( QCA::MemoryRegion *out) override
    {
        QCA::SecureArray lastBlock;
        int numBytesLeft = m_residual.size();

        if ( numBytesLeft != 16 ) {
            // no full block, so we have to pad.
            m_residual.resize(16);
            m_residual[numBytesLeft] = (char)0x80;
            lastBlock = xorArray(m_residual, m_k2);
        } else {
            // this is a full block - no padding
            lastBlock = xorArray(m_residual, m_k1);
        }
        m_Y = xorArray(m_X, lastBlock);
        QCA::Cipher aesObj(QStringLiteral("aes128"),
                           QCA::Cipher::ECB, QCA::Cipher::DefaultPadding,
                           QCA::Encode, m_key);
        *out = aesObj.process(m_Y);

    }

protected:
    // first subkey
    QCA::SecureArray m_k1;
    // second subkey
    QCA::SecureArray m_k2;
    // main key
    QCA::SecureArray m_key;

    // state
    QCA::SecureArray m_X;
    QCA::SecureArray m_Y;

    // partial block that we can't do yet
    QCA::SecureArray m_residual;
};

class ClientSideProvider : public QCA::Provider
{
public:
        int qcaVersion() const override
        {
                return QCA_VERSION;
        }

        QString name() const override
        {
                return QStringLiteral("exampleClientSideProvider");
        }

        QStringList features() const override
        {
                QStringList list;
                list += QStringLiteral("cmac(aes)");
                // you can add more features in here, if you have some.
                return list;
        }

        Provider::Context *createContext(const QString &type) override
        {
            if(type == QLatin1String("cmac(aes)"))
                return new AESCMACContext(this);
            // else if (type == some other feature)
            //  return some other context.
            else
                return nullptr;
        }
};


// AES CMAC is a Message Authentication Code based on a block cipher
// instead of the more normal keyed hash.
// See RFC 4493 "The AES-CMAC Algorithm"
class AES_CMAC: public QCA::MessageAuthenticationCode
{
public:
    AES_CMAC(const QCA::SymmetricKey &key = QCA::SymmetricKey(),
             const QString &provider = QString()):
        QCA::MessageAuthenticationCode( QStringLiteral("cmac(aes)"), key, provider)
    {}
};


int main(int argc, char **argv)
{
    // the Initializer object sets things up, and
    // also does cleanup when it goes out of scope
    QCA::Initializer init;

    qDebug() << "This example shows AES CMAC";

    QCoreApplication app(argc, argv);

    if( ! QCA::isSupported("aes128-ecb") ) {
        qDebug() << "AES not supported!";
    }

    if ( QCA::insertProvider(new ClientSideProvider, 0) )
        qDebug() << "Inserted our provider";
    else
        qDebug() << "our provider could not be added";

    // We should check AES CMAC is supported before using it.
    if( ! QCA::isSupported("cmac(aes)") ) {
        qDebug() << "AES CMAC not supported!";
    } else {
        // create the required object
        AES_CMAC cmacObject;

        // create the key
        QCA::SymmetricKey key(QCA::hexToArray(QStringLiteral("2b7e151628aed2a6abf7158809cf4f3c")));

        // set the MAC to use the key
        cmacObject.setup(key);

        QCA::SecureArray message = QCA::hexToArray(QStringLiteral("6bc1bee22e409f96e93d7e117393172a"
                                               "ae2d8a571e03ac9c9eb76fac45af8e51"
                                               "30c81c46a35ce411e5fbc1191a0a52ef"
                                               "f69f2445df4f9b17ad2b417be66c3710"));
        QCA::SecureArray message1(message);
        message1.resize(0);
        qDebug();
        qDebug() << "Message1: " << QCA::arrayToHex(message1.toByteArray());
        qDebug() << "Expecting:  bb1d6929e95937287fa37d129b756746";
        qDebug() << "AES-CMAC: " << QCA::arrayToHex(cmacObject.process(message1).toByteArray());

        cmacObject.clear();
        QCA::SecureArray message2(message);
        message2.resize(16);
        qDebug();
        qDebug() << "Message2: " << QCA::arrayToHex(message2.toByteArray());
        qDebug() << "Expecting:  070a16b46b4d4144f79bdd9dd04a287c";
        qDebug() << "AES-CMAC: " << QCA::arrayToHex(cmacObject.process(message2).toByteArray());

        cmacObject.clear();
        QCA::SecureArray message3(message);
        message3.resize(40);
        qDebug();
        qDebug() << "Message3: " << QCA::arrayToHex(message3.toByteArray());
        qDebug() << "Expecting:  dfa66747de9ae63030ca32611497c827";
        qDebug() << "AES-CMAC  " << QCA::arrayToHex(cmacObject.process(message3).toByteArray());

        cmacObject.clear();
        QCA::SecureArray message4(message);
        message4.resize(64);
        qDebug();
        qDebug() << "Message4: " << QCA::arrayToHex(message4.toByteArray());
        qDebug() << "Expecting:  51f0bebf7e3b9d92fc49741779363cfe";
        qDebug() << "AES-CMAC: " << QCA::arrayToHex(cmacObject.process(message4).toByteArray());
    }

    return 0;
}

#include "aes-cmac.moc"