# 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>

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

        ~AESCMACContext()
        {
        }

        // 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)
        {
            // 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(QString("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
        {
            return new AESCMACContext(*this);
        }

        void clear()
        {
            setup(m_key);
        }

        QCA::KeyLength keyLength() const
        {
            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)
        {
            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(QString("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)
        {
            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(QString("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
            {
                    return QCA_VERSION;
            }

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

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

            Provider::Context *createContext(const QString &type)
            {
                if(type == "cmac(aes)")
                    return new AESCMACContext(this);
                // else if (type == some other feature)
                //  return some other context.
                else
                    return 0;
            }
    };

    // 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( "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("2b7e151628aed2a6abf7158809cf4f3c"));

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

            QCA::SecureArray message = QCA::hexToArray("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;
    }