C++ (Cpp) CheckSum::get Examples

Example #1

File: DataBlockEncryptor.cpp Project: BackupTheBerlios/multicrew-svn

void DataBlockEncryptor::Encrypt( unsigned char *input, int inputLength, unsigned char *output, int *outputLength )
{
	unsigned index, byteIndex, lastBlock;
	unsigned long checkSum;
	unsigned char paddingBytes;
	unsigned char encodedPad;
	unsigned char randomChar;
	CheckSum checkSumCalculator;
	
#ifdef _DEBUG
	
	assert( keySet );
#endif
	
	assert( input && inputLength );
	
	
	// randomChar will randomize the data so the same data sent twice will not look the same
	randomChar = ( unsigned char ) randomMT();
	
	// 16-(((x-1) % 16)+1)
	
	// # of padding bytes is 16 -(((input_length + extra_data -1) % 16)+1)
	paddingBytes = ( unsigned char ) ( 16 - ( ( ( inputLength + sizeof( randomChar ) + sizeof( checkSum ) + sizeof( encodedPad ) - 1 ) % 16 ) + 1 ) );
	
	// Randomize the pad size variable
	encodedPad = ( unsigned char ) randomMT();
	encodedPad <<= 4;
	encodedPad |= paddingBytes;
	
	*outputLength = inputLength + sizeof( randomChar ) + sizeof( checkSum ) + sizeof( encodedPad ) + paddingBytes;
	
	// Write the data first, in case we are overwriting ourselves
	
	if ( input == output )
		memmove( output + sizeof( checkSum ) + sizeof( randomChar ) + sizeof( encodedPad ) + paddingBytes, input, inputLength );
	else
		memcpy( output + sizeof( checkSum ) + sizeof( randomChar ) + sizeof( encodedPad ) + paddingBytes, input, inputLength );
		
	// Write the random char
	memcpy( output + sizeof( checkSum ), ( char* ) & randomChar, sizeof( randomChar ) );
	
	// Write the pad size variable
	memcpy( output + sizeof( checkSum ) + sizeof( randomChar ), ( char* ) & encodedPad, sizeof( encodedPad ) );
	
	// Write the padding
	for ( index = 0; index < paddingBytes; index++ )
		*( output + sizeof( checkSum ) + sizeof( randomChar ) + sizeof( encodedPad ) + index ) = ( unsigned char ) randomMT();
		
	// Calculate the checksum on the data
	checkSumCalculator.add( output + sizeof( checkSum ), inputLength + sizeof( randomChar ) + sizeof( encodedPad ) + paddingBytes );
	
	checkSum = checkSumCalculator.get();
	
	// Write checksum
	memcpy( output, ( char* ) & checkSum, sizeof( checkSum ) );
	
	// AES on the first block
	secretKeyAES128.encrypt16( output );
	
	lastBlock = 0;
	
	// Now do AES on every other block from back to front
	for ( index = *outputLength - 16; index >= 16; index -= 16 )
	{
		for ( byteIndex = 0; byteIndex < 16; byteIndex++ )
			output[ index + byteIndex ] ^= output[ lastBlock + byteIndex ];
			
		secretKeyAES128.encrypt16( output + index );
		
		lastBlock = index;
	}
}

Example #2

File: DataBlockEncryptor.cpp Project: BackupTheBerlios/multicrew-svn

bool DataBlockEncryptor::Decrypt( unsigned char *input, int inputLength, unsigned char *output, int *outputLength )
{
	unsigned index, byteIndex, lastBlock;
	unsigned long checkSum;
	unsigned char paddingBytes;
	unsigned char encodedPad;
	unsigned char randomChar;
	CheckSum checkSumCalculator;
#ifdef _DEBUG
	
	assert( keySet );
#endif
	
	if ( input == 0 || inputLength < 16 || ( inputLength % 16 ) != 0 )
	{
		return false;
	}
	
	// Unchain in reverse order
	for ( index = 16; ( int ) index <= inputLength - 16;index += 16 )
	{
		secretKeyAES128.decrypt16( input + index );
		
		for ( byteIndex = 0; byteIndex < 16; byteIndex++ )
		{
			if ( index + 16 == ( unsigned ) inputLength )
				input[ index + byteIndex ] ^= input[ byteIndex ];
			else
				input[ index + byteIndex ] ^= input[ index + 16 + byteIndex ];
		}
		
		lastBlock = index;
	};
	
	// Decrypt the first block
	secretKeyAES128.decrypt16( input );
	
	// Read checksum
	memcpy( ( char* ) & checkSum, input, sizeof( checkSum ) );
	
	// Read the pad size variable
	memcpy( ( char* ) & encodedPad, input + sizeof( randomChar ) + sizeof( checkSum ), sizeof( encodedPad ) );
	
	// Ignore the high 4 bytes
	paddingBytes = encodedPad & 0x0F;
	
	
	// Get the data length
	*outputLength = inputLength - sizeof( randomChar ) - sizeof( checkSum ) - sizeof( encodedPad ) - paddingBytes;
	
	// Calculate the checksum on the data.
	checkSumCalculator.add( input + sizeof( checkSum ), *outputLength + sizeof( randomChar ) + sizeof( encodedPad ) + paddingBytes );
	
	if ( checkSum != checkSumCalculator.get() )
		return false;
		
	// Read the data
	if ( input == output )
		memmove( output, input + sizeof( randomChar ) + sizeof( checkSum ) + sizeof( encodedPad ) + paddingBytes, *outputLength );
	else
		memcpy( output, input + sizeof( randomChar ) + sizeof( checkSum ) + sizeof( encodedPad ) + paddingBytes, *outputLength );
		
		
	return true;
}