How to decrypt a string

[abdullah.jobayer]

Hi

I have encrypted string in this way.string1 is encrypted.now i want to decrypt this string.How can i.Is there any one help?

QByteArray string="Nokia";
QCryptographicHash *hash=new QCryptographicHash(QCryptographicHash::Md4);
hash->addData(string);
QByteArray string1=hash->result();

With Regards
jobayer

[isalento]

Hi,

Please correct me if I am wrong, but that class seems to be only for computing "digital fingerprints". For example, you can see if someone has tampered with the data by comparing checksums that are calculated after and before sending the data.

http://en.wikipedia.org/wiki/Cryptog..._hash_function
http://wiki.qtcentre.org/index.php?title=Cryptography

Br,
Ilkka

[james1980]

Hi,

I think there is no such a function for decryption of the encrypted string.

[petrib]

I think there is no such a function for decryption of the encrypted string.

It depends... Typically encryption algorithms also have a corresponding decryption algorithm (if you can't decrypt data, then in most cases encrypting it in the first place is pretty pointless; you might just as well delete the data).

However, as stated in the first reply, a hash function is not encrypting anything; it is using the original data to calculate a fingeprint of the data, but the fingeprint does not contain the actual original data at all.

[abdullah.jobayer]

Thanks to reply

Actually how i can encrypt & decrypt string in QT.

Previously i have done encryption & decryption string by DES algo.

If i so in this is it possible.How i can pls help any one

Jobayer.

[kamalakshan]

AFAIK Qt doesn't have built-in support for encryption but you should be able to use any encryption library.

[abdullah.jobayer]

Thanks to reply.

I am trying by using library.

With Regards
Jobayer

[rahul.shalik.makode]

hi,

i am using cryptography encrypt function

CRSAPKCS1v15Encrypto

iEncryptor.EncryptL( const TDesC8 &aInput,TDes8 &aOutput);

for this function i am passing

TBuf8<2> cipher;
/TBuf8<2> text;

iEncryptor.EncryptL(__L("Hello"),cipher);

but it shows errors

plz any body told me what is mistake while passing args

[kamalakshan]

hi,

i am using cryptography encrypt function

CRSAPKCS1v15Encrypto

iEncryptor.EncryptL( const TDesC8 &aInput,TDes8 &aOutput);

for this function i am passing

TBuf8<2> cipher;
/TBuf8<2> text;

iEncryptor.EncryptL(__L("Hello"),cipher);

but it shows errors

plz any body told me what is mistake while passing args

what is the error you are getting. whether it is runtime or compile time error?

[rahul.shalik.makode]

hi,

i have implemented class using cryptography api,

in that class i have ccreated instance of

iRSAKeyPair = CRSAKeyPair::NewL(aModulusBits, EStandardCRT) ;

const CRSAPublicKey &iRSAPublicKey =iRSAKeyPair->PublicKey() ;

iEncryptor = CRSAPKCS1v15Encryptor::NewL(iRSAPublicKey);

in constructL() of my class

and also called encrypt method

but while creating instance of my class in ui file

it show error

..............error...........

you r opening large file turning on scalability mode might help improve editor performance .plz see scalability mode page under preference->c/c++ editor

...........error.........

i channged scalabilty mode on on for 5000 lines

i have include cryptography.h and lib file

i think b'coz of that size of class goes increasing

and while debuging...it shows error

//...........h file


#ifndef RSAALGO_H_
#define RSAALGO_H_

#include <cryptoasymmetric.h>
#include <signed.h>
#include <cryptopanic.h>
//#include <x509keys.h>

#include <e32base.h>
#include <e32std.h>
#include <cryptobasic.h>
#include <cryptoasymmetric.h>
#include <hash.h>
#include <signed.h>

class CRSAAlgo
{
public:

CRSAAlgo();
virtual ~CRSAAlgo();

public:
static CRSAAlgo* NewL();
static CRSAAlgo* NewLC();

TBool EncryptL(const TDesC8 &aInput, TDes8 &aOutput);

//TBuf16<2> text,cipher;

//void stringToDescriptor(const char* aString, TDes& aDescriptor);

private:

void ConstructL();

protected:

//CRSAPublicKey *iPKey;

//CRSAPKCS1v15Encryptor *iEncryptor;

//CRSAKeyPair *iRSAKeyPair ;

//TUint aModulusBits;


protected:

CRSAKeyPair *iRSAKeyPair ;

CRSAPKCS1v15Encryptor *iEncryptor;

//CRSAPKCS1v15Decryptor iDecrypter;


//CRSAPublicKey iRSAPublicKey ;



//CRSAPrivateKey iRSAPrivateKey ;


//static RInteger iN;
//static RInteger iE;
};

..........................

.............cpp file ...............
/*
* RSAAlgo.cpp
*
* Created on: May 21, 2009
* Author: rahul.makode
*/


/*
* RSAEncryption.cpp
*
* Created on: May 19, 2009
* Author: rahul.makode
*/

#include "RSAAlgo.h"
//#include <cryptopanic.h>

#include <cryptoasymmetric.h>

#include <aknnotewrappers.h>




CRSAAlgo::CRSAAlgo()
{

iRSAKeyPair=NULL;



//iRSAPublicKey = NULL;
//iRSAPrivateKey = NULL;

//iPKey = NULL;
//iEncryptor = NULL;
//iRSAKeyPair=NULL;

//aModulusBits=0;

}
CRSAAlgo::~CRSAAlgo()
{
/*iN.Close();
iE.Close();
if(iEncryptor)
{
delete iEncryptor;
iEncryptor = NULL;
}
if(iPKey)
{
delete iPKey;
iPKey = NULL;
}*/
/* if(iPublic)
{
delete iPublic;
iPublic = NULL;
}
if(iPrivate)
{
delete iPrivate;
iPrivate = NULL;
}*/
}
CRSAAlgo* CRSAAlgo::NewL()
{
CRSAAlgo *self = CRSAAlgo::NewLC();
CleanupStack::Pop(self);
return self;

}


CRSAAlgo* CRSAAlgo::NewLC( )
{
CRSAAlgo *self = new (ELeave) CRSAAlgo;
CleanupStack::PushL(self);



//iN = RInteger::NewL(aN);
//iE = RInteger::NewL(aE);



self->ConstructL();
return self;
}
void CRSAAlgo::ConstructL()
{

TBuf<100> mess;

TUint aModulusBits;

aModulusBits=128;


//iRSAKeyPair=CRSAKeyPair::NewL(aModulusBits);

iRSAKeyPair = CRSAKeyPair::NewL(aModulusBits, EStandardCRT) ;

const CRSAPublicKey &iRSAPublicKey =iRSAKeyPair->PublicKey() ;

iEncryptor = CRSAPKCS1v15Encryptor::NewL(iRSAPublicKey);



mess.Append(_L("public key:"));

//TInt num(-6);
//TBuf<8> des;
//take care of number of digits. if it exceed defined in TBuf<>, 8 here, it gives panic.
//des.Num(iRSAPublicKey);

//mess.Copy(des);


//TBuf<32> buffer; // Make it large enough for str

//stringToDescriptor(str, text);

TBuf8<10> text;

TBuf8<10> cipher;

text.Copy(_L("Hello"));

/* TBuf8<64> plaintext;

plaintext.Append(_L("Hello"));


HBufC8* plainText = HBufC8::NewLC(64);
TPtr8 plainTextPtr = plainText->Des();*/

//iEncryptor.
EncryptL(text,cipher);

mess.Append(_L("encrypted string"));

mess.Copy(cipher);


// iEncryptor.EncryptL(plainTextPtr,cipher);




//mess.Append(cipher);

//TBuf8<64> plaintext;

//mess.AppendNum(iRSAPublicKey);


//mess.AppendNum(TInt64(iRSAPublicKey ));

//mess.AppendNum(iRSAPublicKey);

const CRSAPrivateKey &iRSAPrivateKey =iRSAKeyPair->PrivateKey();

//iDecrypter = CRSAPKCS1v15Decryptor::NewL(iRSAPrivateKey);

TInt err;

CRSAPKCS1v15Decryptor * decryptor;

TRAP(err,decryptor= CRSAPKCS1v15Decryptor::NewLC(iRSAPrivateKey));




mess.Append(_L("private key:"));


//mess.Copy(iRSAKeyPair);


CAknInformationNote* note = new (ELeave) CAknInformationNote;

// note->SetTimeout( CAknNoteDialog::ELongTimeout );

// TBuf<0x100> buf;

// buf.Format( _L("HandleGetByAttributeL( %i )"), aStatus );

note->ExecuteLD( mess);




//iRSAPublicKey = i
//iRSAPrivateKey = iRSAKeyPair->PrivateKey();



/*iPKey = CRSAPublicKey::NewL(iN,iE);
*
*

if(iPKey)
{
iEncryptor = CRSAPKCS1v15Encryptor::NewL(*iPKey);
}
*/
/*iPrivate=iRSAKeyPair.PrivateKey();
iPublic=iRSAKeyPair.PublicKey();

console->Printf(iPrivate);

console->Printf(iPublic);*/


//iRSAKeyPair.PrivateKey();
//iRSAKeyPair.iPrivate=iPrivate=iRSAKeyPair.PrivateKey();


//iPrivate=
//iRSAKeyPair.PrivateKey();


//iPublic=iRSAKeyPair.PublicKey();



}

TBool CRSAAlgo::EncryptL(const TDesC8 &aInput,TDes8 &aOutput)
{
if(iEncryptor)
{
TInt len = iEncryptor->MaxInputLength();
if(aInput.Length() > len)
return false;

TRAPD(retval,iEncryptor->EncryptL(aInput,aOutput));
if(retval != KErrNone)
{
switch(retval)
{
case ECryptoPanicOutputDescriptorOverflow:
{
retval = 0;
}
break;
case ECryptoPanicPadInputTooLarge :
{
retval = 1;
}
break;
case ECryptoPanicInputTooLarge :
{
retval = 2;
}
break;
default:
retval = 3;
}
return false;
}

return true;
}

return false;
}
/*

void CRSAAlgo:ecryptL(const TDesC8 &aInput, TDes8 &aOutput)
{

}
*/

/*
void CRSAAlgo::stringToDescriptor(const char* aString, TDes& aDescriptor)
{
TPtrC8 ptr(reinterpret_cast<const TUint8*>(aString));
aDescriptor.Copy(ptr);
}*/


.........................

i am using cryptography api plz sugest me how to used cryptography api in our class

[kamalakshan]

What is the error you are getting. Also there is an example in wiki I think related to cryptography api.

[rahul.shalik.makode]

my application is crashing on emulator

1)no souce code (strong_cryptography.dll) not found

i have added the .h and lib for cryptography api

2)also if there is any prob for passing values to encyptl()

i dont know exact prob

[kamalakshan]

When crashing do you get any panic code. Please check this.