# publickeyexample.cpp

The code below shows how to do public key encryption, decryption, signing and verification.

    /*
     Copyright (C) 2003 Justin Karneges <justin@affinix.com>
     Copyright (C) 2005 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.
    */

    #include <QtCrypto>

    #include <QCoreApplication>

    #include <iostream>

    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;

        QCoreApplication app(argc, argv);

        // We need to ensure that we have certificate handling support
        if ( !QCA::isSupported( "cert" ) ) {
            std::cout << "Sorry, no PKI certificate support" << std::endl;
            return 1;
        }

        // Read in a private key
        QCA::PrivateKey privKey;
        QCA::ConvertResult convRes;
        QCA::SecureArray passPhrase = "start";
        privKey = QCA::PrivateKey::fromPEMFile( "Userkey.pem", passPhrase, &convRes );
        if ( convRes != QCA::ConvertGood ) {
            std::cout << "Sorry, could not import Private Key" << std::endl;
            return 1;
        }

        // Read in a matching public key cert
        // you could also build this using the fromPEMFile() method
        QCA::Certificate pubCert( "User.pem" );
        if ( pubCert.isNull() ) {
            std::cout << "Sorry, could not import public key certificate" << std::endl;
            return 1;
        }
        // We are building the certificate into a SecureMessageKey object, via a
        // CertificateChain
        QCA::SecureMessageKey secMsgKey;
        QCA::CertificateChain chain;
        chain += pubCert;
        secMsgKey.setX509CertificateChain( chain );

        // build up a SecureMessage object, based on our public key certificate
        QCA::CMS cms;
        QCA::SecureMessage msg(&cms);
        msg.setRecipient(secMsgKey);

        // Some plain text - we use the first command line argument if provided
        QByteArray plainText = (argc >= 2) ? argv[1] : "What do ya want for nuthin'";

        // Now use the SecureMessage object to encrypt the plain text.
        msg.startEncrypt();
        msg.update(plainText);
        msg.end();
        // I think it is reasonable to wait for 1 second for this
        msg.waitForFinished(1000);

        // check to see if it worked
        if(!msg.success())
        {
            std::cout << "Error encrypting: " << msg.errorCode() << std::endl;
            return 1;
        }

        // get the result
        QCA::SecureArray cipherText = msg.read();
        QCA::Base64 enc;
        std::cout << plainText.data() << " encrypts to (in base 64): ";
        std::cout << qPrintable( enc.arrayToString( cipherText ) ) << std::endl;

        // Show we can decrypt it with the private key
        if ( !privKey.canDecrypt() ) {
            std::cout << "Private key cannot be used to decrypt" << std::endl;
            return 1;
        }
        QCA::SecureArray plainTextResult;
        if ( 0 == privKey.decrypt(cipherText, &plainTextResult, QCA::EME_PKCS1_OAEP ) ) {
            std::cout << "Decryption process failed" << std::endl;
            return 1;
        }

        std::cout << qPrintable( enc.arrayToString( cipherText ) );
        std::cout << " (in base 64) decrypts to: ";
        std::cout << plainTextResult.data() << std::endl;

        return 0;
    }