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;
}
}
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;
}