[Qt-interest] QCA big string encryption

[Jason H]

Generally you need an IV (Initialization vector) this then is fed to the 
routines with the keys. The IV is an important random number so that if you can 
encrypt the same message with the same keys multiple times and not get the same 
encrypted message (thus ruling out a dictionary attack)

Anyway, there are two types of cyphers, block and stream. With block cyphers, 
you work a block at a time. The last block will usually be incomplete, and there 
is some final[ize[() method for handling this special block. Normally, the 
enc/decrypt functions in QCA will give you all complete blocks, leaving you to 
call finalize().

QCA does have convince functions that will do it all without you having to call 
finalize(), HOWEVER this should only be used for messages of known, short 
lengths. The non-convenience functions are designed to be used in a streaming 
manner, which is better for memory and scalability. 



HTH, but AFAIAC, this is a QCA question, not a Qt question.




----- Original Message ----
From: Nicholas Shatokhin <n.shatokhin at gmail.com>
To: qt-interest at qt.nokia.com; Jason H <scorp1us at yahoo.com>
Sent: Sun, April 24, 2011 2:52:53 PM
Subject: Re: [Qt-interest] QCA big string encryption

What do you mean?

There is my code below. What must I add? (I use 1024bit rsa key and message 
truncate to 1024bit)


bool CCryptor::generateKeys(int size)
{
    if(init())
    {
        QCA::PrivateKey seckey = QCA::KeyGenerator().createRSA(size);

        if(seckey.isNull())
        {
            std::cout << "Failed to make private RSA key" << std::endl;
            return false;
        }

        QCA::PublicKey pubkey = seckey.toPublicKey();

        privateKey = seckey;
        publicKey = pubkey;

        return true;
    }
    else
        return false;
}

QByteArray CCryptor::dataEnrypt(QByteArray data)
{
    // check if the key can encrypt
    if(!publicKey.canEncrypt())
    {
        std::cout << "Error: this kind of key cannot encrypt" << std::endl;
        return QByteArray();
    }

    QCA::SecureArray arg = data;

    // encrypt some data - note that only the public key is required
    // you must also choose the algorithm to be used
    QCA::SecureArray result = publicKey.encrypt(arg, QCA::EME_PKCS1_OAEP);

    if(result.isEmpty()) {
        std::cout << "Error encrypting" << std::endl;
        return QByteArray();
    }

    return result.toByteArray();
}

QByteArray CCryptor::dataDecrypt(QByteArray data)
{
    QCA::SecureArray encrypt = data;
    QCA::SecureArray decrypt;
    if(0 == privateKey.decrypt(encrypt, &decrypt, QCA::EME_PKCS1_OAEP))
    {
        std::cout << "Error decrypting.\n";
        return QByteArray();
    }

    return decrypt.data();
}



Sun, 24 Apr 2011 21:31:38 +0300 було написано Jason H <scorp1us at yahoo.com>:

> It's beena  while since I used QCA, but do you need to finalize() it for the
> last block?
> 
> 
> 
> 
> ----- Original Message ----
> From: Nicholas Shatokhin <n.shatokhin at gmail.com>
> To: qt-interest at qt.nokia.com
> Sent: Sun, April 24, 2011 1:12:41 PM
> Subject: [Qt-interest] QCA big string encryption
> 
> Hello.
> 
> I'm trying to encrypt end decrypt long string. But after decryption, I get
> only part of string. What's wrong?
> 
> Code:
> 
>      QCA::SecureArray arg = data;
>      qDebug() << arg.toByteArray();
>      QCA::SecureArray result = publicKey.encrypt(arg, QCA::EME_PKCS1_OAEP);
>      privateKey.decrypt(result, &arg, QCA::EME_PKCS1_OAEP);
>      qDebug() << arg.toByteArray();
> 
> Output:
> 
> "{"method": 1, "data": {"email": "dfgh", "usePassword": "false",
> "password": "", "useFingerprint": false, "fingerprint": "", "publicKey":
>"LS0tLS1CRUdJTiBQVUJMSUMgS0VZLS0tLS0KTUlHZk1BMEdDU3FHU0liM0RRRUJBUVVBQTRHTkFEQ0JpUUtCZ1FDN05UNjd6R1pHajZpbDc5K3ErOWo5K2s5cApnVHJJOGxRVlFoQkxuVWxBNFArS01selBEOU9aOEk0UXRWNEdjT0ZOYWFyTjByZFlacllKaVF2VjBUQkdSSnRWCnNEOTVsZzNPMHFzVHBuSVdrYW5rUTVFUmdiTDlqQ0grb0taNFBrUEd0OW9MVjhCOGphNjFRazdhLytBVUZ1UUQKeDBMUGZvUyt5VkVoYXNjM0x3SURBUUFCCi0tLS0tRU5EIFBVQkxJQyBLRVktLS0tLQo="}
>}
> }"
> 
> "{"method": 1, "data": {"email": "dfgh", "usePassword": "false",
> "password": "", "useFi"
> 
> 
> Best regards,
> Nick.
> 


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