Multimedia Fusion and Blowfish

Multimedia Fusion is a great program made by a company called Clickteam. If you’ve ever heard of Klik ‘n’ Play, Multimedia Fusion (MMF) is the latest version of that. I started using Klik ‘n’ Play way back in the late 90s (probably 1998). I made some pretty bad games with it, which are still available for download on my web page. About a year later, I purchased my first copy of MMF and discovered that the makers of the software had their own web site and community. I never made any particularly good software with MMF, which is not to say MMF is incapable of good software. It is. In fact, several people I know have made successful commercial ventures with games they made in MMF. I really found my niche in the community when I started learning C++ the summer before my senior year in high school. Suddenly, I could make extensions for MMF, adding new functionality to the program. I may not have been much of a game maker, but I wasn’t too bad with making useful extensions. Eventually, I developed a relationship with some members of the company. In fact, they’ve sent me a few free copies of their software over the years. Alas, over time, I grew apart from MMF and the community. Throughout college, I focussed more and more on traditional programming paradigms and less on MMF. I preferred the more flowing structure of languages like C++ than the event list structure of MMF.

Eventually, I lost all contact with the community. This is something I regret quite a bit. Occasionally, I would get e-mails from people asking about my extensions but not too often. Back in 2008, I was made aware of a bug in one of my extensions, the Blowfish encryption object. This is the one extension that I had actually sold to Clickteam, so when I decided that I would try to fix the bug, I had to get a copy of the source from them. I actually found and fixed the bug. It turns out that the Blowfish algorithm expects data in big-endian form (I’ll discuss this more later), so I just needed to reverse the byte ordering before and after encryption. I did this, but then I got an even bigger idea in my head. It seems silly that each object that wants to use encryption should have to implement the algorithm itself. What if there were a generalized encryption system where any object that wanted to encrypt data could simply be passed the information of an encryption object and could then make use of the encryption object’s own algorithms? Well, I set about working on that model and got in over my head. After a while, I gave up and never returned the fixed source code to Clickteam. I was in a time in my life where motivation is difficult to find. Years passed. I’m finally now trying to dig myself out of this rut. In fact, this blog is one of the ways I’m trying to do it. I figure that the more I tell people what I’m doing, the more likely I am to follow through with it. Granted, no one reads this blog, but maybe, some day, someone will. I consider not correcting the bug in the Blowfish object to be a significant failing on my part, so finally fixing it is of great importance to my sense of self-wroth.

The bug in question, as mentioned earlier, had to do with the byte ordering of data sent to the encryption/decryption functions. If you don’t plan to use any encrypted data with any other implementations of Blowfish, this isn’t actually a problem, but it is likely that you’d want to do that. When passing data (stored as an array of characters) to the Blowfish functions, I would just typecast addresses into the array as pointers to unsigned longs. In little-endian formats, this puts the first character as the lowest byte of the newly formed long. It seems that Blowfish implementations prefer that this first character be in the highest byte of the long. I’m not entirely sure if this means that Blowfish implementations prefer big-endianness or if it’s simply that they convert the array of characters using bit-shifts and ors rather than simple typecasts. I wasn’t satisfied, however, with just fixing this bug. I wanted to add some different cipher block modes. In the past, I had only used the electronic codebook mode (ECB) because I simply wasn’t aware of the other modes in use. At first, I was only going to add cipher-block chaining mode (CBC), but after further investigation, I realized that cipher feedback mode (CFB) and output feedback mode (OFB) were relatively simple to implement. I decided to add all three new modes to the object. I’m not sure what the relative advantages and disadvantages are of each mode, but since they were so simple to add, I decided to just add them and let the user sort it out.

I also wanted to rewrite the file-handling function. In my younger days, I seemed to have a strange dislike of keeping files open, so I would read entire files into memory and then process the data. Once done, I would reopen the file and write the new data. For small files, this is fine, but for large files, this can be problematic. In rewriting the function, I had to open the file in both read and write modes. I had never used a file in this manner before and was unaware of one of the quirks involved. In my first tests, I was able to read and write my first block of data, but I was unable to read subsequent blocks. My first test took a little 1.82 MB file and turned it into a gigantic 64 MB file because I would keep reading and writing the same block of data over and over. After some research, I discovered than when switching between using fread and fwrite, you need to have a call to fseek. Before writing data back to the file, I would call fseek to jump back to the start of the block, but since the write operation placed me at the location in the file of the next block of data to read, I had no reason to call fseek again. Because an fseek call is required before switching back to fread, I had to add a dummy call to fseek that doesn’t change my position in the file. After fixing that problem, my updated file handling worked perfectly.

I took me nearly a week to make and debug all of the changes that I wanted, but I feel it was worth it to remove this blemish from my psyche. I’ve returned the updated object to Clickteam to see what they think of the update object.