[Qt-interest] QCA big string encryption

[Jason H]

Ah, good observation.

It should be know that SSL only uses asymmetric encryption for key and cypher 
exchange. The stream itself uses a shared-secret cypher.




----- Original Message ----
From: Jeroen De Wachter <jeroen.dewachter at elis.ugent.be>
To: Nicholas Shatokhin <n.shatokhin at gmail.com>
Cc: qt-interest at qt.nokia.com
Sent: Sun, April 24, 2011 5:14:20 PM
Subject: Re: [Qt-interest] QCA big string encryption

Hey Nicholas,

Have you seen the maximumEncryptSize function in PublicKey?
Your string might simply be too big...

http://delta.affinix.com/docs/qca/classQCA_1_1PublicKey.html#175b61ba787f95146b5971295120f8b8


Also, AFAIK asymmetric encryption algorithms are usually used on small
amounts of data because of their intense CPU load. IIRC, they are
typically used to encrypt the key of a symmetric encryption algorithm,
which is usually easier on the CPU (and thus faster for processing
copious amounts of data). Can you tell us why you would need to process
such a large string?

Kind regards,

Jeroen

On Sun, 2011-04-24 at 22:15 +0300, Nicholas Shatokhin wrote:
> I'm sorry, but I must finish it in few hours and I don't know how.
> 
> Sun, 24 Apr 2011 22:06:22 +0300 було написано Jason H <scorp1us at yahoo.com>:
> 
> > 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.
> >>
> >
> >
> > --За використання революційного клієнта електронної пошти Opera:
> > http://www.opera.com/mail/
> >
> 
> 





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