The hidden world
A second contest was planned with a different password that would unlock a different 6th level. That password was never revealed publicly.
By editing RAM at runtime, we were able to bypass the password check and see what the level looks like:
Why a brute-force search
By reverse-engineering the game's password-processing routine we understand the complexity. A 24-character password that is entered is transformed into 8 bytes. Those bytes go through many rounds of processing, the result gets XORed against a chunk of memory in the game's ROM, and the output is 6502 assembly which makes the world function.
The XOR step makes the encryption a one-time pad. Without the password we can't know what the assembly code should be. We have taken an educated guess at what the code could look like, and managed to get the level into a partially functional state, but we're not sure it's correct since the one-time pad is cryptographically perfect. And even if we had the final output, the complexity of the rounds makes it very difficult to work backwards through the processing.
Instead, to find the password we are trying every possible 8-byte input and checking the result. This project distributes the search space across volunteer machines. Each contributor is given a small range, tries every candidate in that range, and reports back whether any input passes the game's password check. With enough help we may be able to try them all and find the password.
About me
I'm micro500. I've been working on this on and off for over 20 years. From the moment I found out about the unseen world I was hooked. I found the idea of a secret world that had never been seen before fascinating, and I wanted to make it accessible the way the contest would have.