This is pretty cool, I wasn’t aware of these types of challenges. How does one even approach this?
Feels to me like it’s similar to dumping a binary with an image, the format being entirely custom.
And/or trying to decode a language or cipher, trying to recognize patterns.
I was one of the solvers. It took me about a week to figure out. This is what I wrote out in my submission with the answer:
> After looking at the final two layers I was somewhat quick to intuit that this was some sort of password check, but wasn’t entirely sure where to go from there. I tried to reverse it, but it was proving to be difficult, and the model was far too deep. I started evaluating the structure and saw the 64 repeated sections of 84 layers that each process 4 characters at a time. Eventually I saw the addition and XOR operations, and the constants that were loaded in every cycle, and the shift amounts that differed between these otherwise identical sections.
> I thought it was an elaborate CTF cryptography challenge, where the algorithm was purposely weak and I had to figure out how to exploit it. But I repeatedly was getting very stuck in my reverse-engineering efforts. After reconsidering the structure and the format of the ‘header' I decided to take another look at existing algorithms...
Basically it took a lot of trial and error, and a lot of clever ways to look at and find patterns in the layers. Now that Jane Street has posted this dissection and 'ended' this contest I might post my notebooks and do a fuller post on it.
The trickiest part, to me, is that for about 5 of the days was spent trying to reverse-engineer the algorithm... but they did in fact use a irreversible hash function, so all that time was in vain. Basically my condensed 'solution' was to explore it enough to be able to explain it to ChatGPT, then confirm that it was the algorithm that ChatGPT suggested (hashing known works and seeing if the output matched) and then running brute force on the hash function, which was ~1000x faster to compute than the model.
Did you get an interview with Jane Street?
Yeah, they put me on the quant researcher track. Made it to the final round onsite, but they did not extend an offer T_T
Study math/statistics/ML at a graduate level, to start.
TFA details a solution, it's pretty interesting. Basically the problem was to reverse engineer an absurdly obfuscated and slightly defect MD5 algorithm.