Obfuscate data

gistfile1.txt

// Fill this out with whatever you want. Use the same string
// and algorithm to scramble the files on the server.
static unsigned char secretString[SECRET_STRING_LENGTH];

- (NSData *)scrambleOrDescrambleData:(NSData*)input
{
    unsigned char *outputBytes = malloc(input.length);
    memcpy(outputBytes, input.bytes, input.length);
    for (int i = 0; i < input.length; i++)
    {
        outputBytes[i] = outputBytes[i] ^ secretString[i % SECRET_STRING_LENGTH];
    }

    NSData *outputData = [[NSData alloc] initWithBytes:outputBytes length:input.length];
    free(outputBytes);

    return outputData;
}