fileencryption.cpp

S60DeploymentLabEx3,有兴趣的同学可以自己研究研究

/* Copyright (c) 2003, Nokia Mobile Phones. All rights reserved */
#include <s32file.h>
#include <s32crypt.h>

#include "FileEncryption.h"

const TUint16 KArray[] = {0x1234, 0xFABC, 0xD00A, 0x0D8A, 0xA760, 0x0012, 0x2283, 0x1839, 0xBAAD, 0xC623};

// Maximum length of the key data
const TInt KMaxKeyDataLength = 2048;

// Maximum length of the message
const TInt KMaxPlainTextDataLength = 1024;

CFileEncryption* CFileEncryption::NewL()
    {
    CFileEncryption* self = NewLC();
    CleanupStack::Pop(self);
    return self;
    }

    
CFileEncryption* CFileEncryption::NewLC()
    {
    CFileEncryption* self = new (ELeave) CFileEncryption();
    CleanupStack::PushL(self);
    self->ConstructL();
    return self;
    }


CFileEncryption::CFileEncryption()
    {
    }


CFileEncryption::~CFileEncryption()
    {
    iFileSession.Close();
    }


void CFileEncryption::ConstructL()
    {
    User::LeaveIfError(iFileSession.Connect());
    }


void CFileEncryption::CreateFileL(const TDesC& aFileName, const TDesC& aFileData, const TDesC& aKey)
    {
    if (aFileData.Length() > KMaxPlainTextDataLength)
        {
        // leave if the data to encrypt is too long
        User::Leave(KErrOverflow);
        }
    TParse parse;
    parse.Set(aFileName, NULL, NULL); // parse the directory from the full pathname
    TPtrC path = parse.Path();
    iFileSession.MkDir(path); // Ignore return value

    RFile file;
    User::LeaveIfError(file.Replace(iFileSession, aFileName, EFileWrite));
    CleanupClosePushL(file);

    // Set up the encryption engine with the supplied key
    CBoundedSecurityBase* encrypter = Security::NewL();
    CleanupStack::PushL(encrypter);

    HBufC* garble = GarbleKeyLC(aKey);
    encrypter->SetL(KNullDesC, *garble);
    CleanupStack::PopAndDestroy(); // garble

    // Write the data to be encrypted to a file stream
    RFileWriteStream outputFileStream(file);
    CleanupClosePushL(outputFileStream);
    // must use streaming api not WriteL
    outputFileStream << encrypter->SecurityData(); 

    // Write the data in the stream to an encrypted format
    REncryptStream encryptedFileStream;
    encryptedFileStream.AttachLC(outputFileStream, *encrypter, KNullDesC8); 
    encryptedFileStream << aFileData;
    encryptedFileStream.Close();
    encryptedFileStream.Pop();

    // Clean up
    CleanupStack::PopAndDestroy(); // close outputFileStream
    CleanupStack::PopAndDestroy(); // encrypter
    CleanupStack::PopAndDestroy(); // close file 
    }

HBufC* CFileEncryption::ReadFileL(const TDesC& aFileName, const TDesC& aKey)
    {
    // open file containing encrypted data
    RFile file;
    User::LeaveIfError(file.Open(iFileSession, aFileName, EFileRead));
    CleanupClosePushL(file);

    RFileReadStream inputFileStream(file);
    CleanupClosePushL(inputFileStream);

    // read the security data 
    HBufC8* securityData = HBufC8::NewLC(inputFileStream, KMaxKeyDataLength);

    // create security object, using the read security data
    CBoundedSecurityBase* decrypter = Security::NewL(*securityData); 
    CleanupStack::PopAndDestroy(); // securityData

    CleanupStack::PushL(decrypter);

    // authenticate password
    HBufC* garble = GarbleKeyLC(aKey);
    decrypter->PrepareL(*garble);
    CleanupStack::PopAndDestroy(); // garble
    

    // Read the encrypted data
    RDecryptStream decryptedFileStream;
    decryptedFileStream.AttachLC(inputFileStream, *decrypter, KNullDesC8); 
    CleanupClosePushL(decryptedFileStream);
    HBufC* decryptedData = HBufC::NewL(decryptedFileStream, KMaxPlainTextDataLength);

    CleanupStack::PopAndDestroy(); // close decryptedFileStream
    decryptedFileStream.Pop(); // removes item placed on cleanup stack by AttachLC
    CleanupStack::PopAndDestroy(); // decrypter



    CleanupStack::PopAndDestroy(); // close inputFileStream 
    CleanupStack::PopAndDestroy(); // close file 

    return decryptedData;
    }


HBufC* CFileEncryption::GarbleKeyLC(const TDesC& aKey)
    {
    TInt len = aKey.Length();
    if (!len)
        {
        User::Leave(KErrArgument);
        }
    HBufC* ret = HBufC::NewLC(len);
    *ret = aKey;
    TPtr ptr = ret->Des();
    for (TText i = 0; i < len; i++)
        {
        TText ch = ptr[i];
        ch = static_cast<TText>((ch + i) * 2 / (i + 1));
        while (ch > 'z')
            {
            ch = static_cast<TText>(ch - i - 1);
            }
        while (ch < ' ')
            {
            ch = static_cast<TText>(ch + i + 1);
            }
        ptr[i] = ch;
        }
    return ret;
    }