Bisqwit's NES game hacking

More than ten years ago, perhaps around the years 1990-1991, I played NES games a lot.
Mega Man 2 was the first game ever I hacked. I deciphered this code system by myself without any help from game magazines (if I ever read any) or such. I am still quite proud of it ;)
It was the time before I ever had used computers.
However because of the success in this game, I then tried to hack almost all games that ever contained a password system... I had some success, some failures.

The decoder/encoder is here (requires javascript support).

Similar to Mega Man 2, I tried hacking this game, and I succeeded.

At those years, I had never used a computer yet. I had no programming experience whatsoever. Seems so distant now...

All of the work was done on a real NES-clone, paper and pen.

The decoder/encoder is here (requires javascript support).

I tried to hack this game, but I didn't figure it out. The only thing I got was a few working guesses.

Many years later, now that I have read how it works, it's so simple...

The decoder/encoder is here (requires javascript support).

I have spent countless hours hacking this game. All without a computer of course. I could alter the number of garlics and the time, but I didn't figure it out.

I wrote up many passwords - same password in different encoding, same encoding with slightly different passwords... to see how different factors change it. I didn't know about the concept of "bit" yet, and I was doing it all on paper.

This all changed in 2004.

In June 3th, Hitek contacted me saying he has solved Castlevania 2. I took a look at his encoder-decoder, and analyzed it thoroughly. It wasn't very beautiful code, and it only handled one special case of the encodings of the game, but it got me started. I wrote my own version based on his code.

I analyzed how the code works. I found that it uses some kind of xor+add encoding, and I started to look for methods to find the rest of the encodings.

I didn't progress until September 2004, when I took a concrete approach and disassembled the game. I found something that I didn't happen to think - the different encodings are actually based on tables of xor values.
Now, Castlevania 2 password system is completely solved with no left mysteries.

The decoder/encoder is here (requires javascript support).

Solar Jetman is extremely simple. It's quite easy to come up with working passwords by chance - but I didn't solve it until with TNSe's help in September 2004. However, the checksum calculation was still broken until March 2006, when I looked it up from the ROM after a prod to the right direction by David Lawrence Ramsey. It works now perfectly.

The decoder/encoder is here (requires javascript support).

This is another game with countless hours of hacking during the precious years before any computer experience. Despite all the effort, the password system of this game is still a mystery.

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[1]: Page created by Joel Yliluoma.