3 ms·
Reversing Factorio's RNG
- pema99 2mo agoSuper cool
- jvanderbot 2mo agoYeah, no notes. It's remarkable. TL;DR: Wired up an in-game predictor of RNG output and used it to only craft legendary items when RNG would line up to roll legendary. From base to legendary at a suprisingly high rate. Look very closely at the video at the top of the post - what I was seeing didn't sink in until I had finished the article. Amazing.
- lowbloodsugar 2mo agoMadman. Brilliant.
- strstr 2mo agoI did an easier version of this in my college intro class. There was a class competition that involved rock paper scissors as a subcomponent, and ties were broken with randomness. You could rig Java’s prng so you would win all ties. The prng was seeded with usec time at first call. I called the rng a bunch of times to harvest entropy, and scanned the plausible usec times to find the seed. Then I primed the prng so I would win ties. Frankly, I assume I implemented this wrong, but the theory was there lol.
- rogueaine 2mo agoThat’s not at all what the article proposed. The author constructed and transpose to the linear shift register coefficients and built a circuit network based on this to predict the next state (in the sandbox) and direct recipes.
- strstr 2mo agoFrom the article: > Sampling the current RNG through observations, > Computing the current internal RNG state, > Predicting the future internal states, > Calculating corresponding quality levels for each future call, and finally > Making use of the predicted levels with some adapters. The entropy->seeds (internal RNG state) step took more math of course. Frankly, I wouldn’t be surprised if they could have extracted the seeds without the math with a bit of RE and memory inspection. The version I did wasn’t predicting quality of course, it was predicting tie breakers
- 3eb7988a1663 2mo agoI am failing to find the article, but some early online poker systems used the server time as the seed coupled with a weak PRNG. With the information of the hole cards + community cards, after a few hands, could quickly determine exactly what seed was being used and perfectly predict everyone's cards.
- e28eta 2mo agoI don't think this was the original source, but this paper matches your (& my) recollection: https://gwern.net/doc/cs/cryptography/2006-arkin.pdf https://gwern.net/doc/cs/cryptography/2006-arkin.pdf google surfaces a couple of HN posts, but the source (cigital.com) seems to be a dead domain at this point: https://news.ycombinator.com/item?id=288138 https://news.ycombinator.com/item?id=288138 https://news.ycombinator.com/item?id=9914607 https://news.ycombinator.com/item?id=9914607 It's a bad shuffle implementation + using time of day as seed (reducing search space). Using the player's 2 cards and the 3 flop cards, it finds the RNG seed in real time, and then future hands (on the same server) are solved in "under one second!"
- 3eb7988a1663 2mo agoIndeed this is not the article I originally read either, but very similar breakdown of the problem.
- myhf 2mo agoImpressive work!
- PennRobotics 2mo agoStardew Valley has two random number seeds. One is the normal character seed. The other, your multiplayer ID, can be determined by analyzing the save file. Except! On the Switch, you can't easily access the save file AND the random number generator is different than on PC. There is a seed cracker that looks at your traveling cart listing and calculates the character seed. Maybe because it's less important and harder to observe, I haven't found any tool to crack the other seed and don't have time to attempt writing it myself. By inspecting cracked geode contents, you should be able to isolate your multiplayer ID and then predict random events on Nintendo just as PC players have done for the last decade with access to the save file. The C# code for the game is online and the Switch RNG is known, so you never have to work in the dark. It's three steps: ensure your Switch RNG implementation works by testing against the normal seed, ensure your geode RNG implementation works by testing against the PC RNG, and then apply the Switch RNG to the geode function enough times that only one seed could create your observed sequence. ----- Two semi-related open questions: Are you able to solve as quickly while starting at ANY geode as you'd be solving from the first geode? Does the RNG eventually repeat, so it actually doesn't matter what your multiplayer ID is as long as you observe a unique sequence, since there will only be one continuation of that sequence?
- bombcar 2mo agoMy favorite is the Doom random number generator, which is just a list of “random” numbers that it cycles through and if you know how to use it, you can do things like concentrate BFG attacks.
- nomel 2mo agoReminds me of a "Dice" electronics kit I assembled when I was a kid. It just used some standard sequential counter ICs run at very high rate. Pressing the "roll" button would just stop the counter!
- xoxxala 2mo agoEverQuest also used pre-generated numbers. The randomness was derived from the large number of players using the same list.
- vlyan 2mo agoby far the blackest magic I ever saw for that game. I'm an upper intermediate at Factorio, resorting to someone else's blueprints only for belt balancers and rail intersections, and I can't even begin to figure out how it's done.
- Aardwolf 2mo ago> We chose taus88 mainly because it is the fastest from boost’s generators. That's an RNG from 1996. It seems neither recent C++ standards, nor boost, know anything about the modern PRNGs that are much faster yet better at passing test suites EDIT: Ok the above quote was from 2014, and boost seems to know some now! https://www.boost.org/doc/libs/latest/doc/html/boost_random/reference.html https://www.boost.org/doc/libs/latest/doc/html/boost_random/...
- Founderarcstone 2mo agoReally cool example of how something that looks random can become predictable once you understand the underlying system.
- jason_s 2mo agoneat! more info on LFSRs, fyi: https://www.embeddedrelated.com/showarticle/1309.php https://www.embeddedrelated.com/showarticle/1309.php
- hbroom 2mo agoDedication like this is awesome. Finally, we can optimize those starting resource patches without endless map restarts!
- 3eb7988a1663 2mo agoAt the conclusion, he said he spent two years on this! That's a thesis.
- throooooo 2mo agoIf you're playing/hosting locally you get a preview of the world and can reroll for a different seed if you'd like.
- torvin92 2mo agoAs if Factorio wasn't addictive enough, now we can predict ore patches! My sleep schedule is already ruined.
- harlan_pdx 2mo agoFactorio players reverse-engineering an RNG? Peak Factorio. The dedication to optimize everything, even randomness, is truly something.
- jatins 2mo agoWhat’s the goal here with posting AI comments on every post? Does it help you get a job, do you sell this account?
- redbear2026 2mo agoIt's probably just a test for their bot. We will see them everywhere.
- jatins 2mo agoit works! others can stop the test now
- cmovq 2mo agoOne of the reasons I dislike boost is in the first code sample. What’s the point of implementing what boils down to a 10 line function (as shown in the decompiled output) like this typedef xor_combine_engine< xor_combine_engine< linear_feedback_shift_engine<uint32_t, 32, 31, 13, 12>, 0, linear_feedback_shift_engine<uint32_t, 32, 29, 2, 4>, 0>, 0, linear_feedback_shift_engine<uint32_t, 32, 28, 3, 17>, 0> taus88;
- mitxela 2mo agoBoost predates C++11
- ainiriand 2mo agoC++ is uglier than punching one's dad.
- windenntw 2mo agoCorrect, but also beside the point. To do it in almost-plain C, you'd need fairly complex macros that are more difficult to write correctly. To do it in plain C without macros, or plain C++ without templates... you'd need to work out the combination of the template expansion yourself and write down a piece of code that is more likely to have bugs and more difficult to understand.
- eru 2mo agoI'm not quite sure: you could probably use plain C functions, and a reasonably smart compiler could see through it all and inline and duplicate and merge the code as necessary. EDIT: I just had an AI agent run the experiment. At least for my version of clang, they produce the same assembly for x86_64 (modulo using slightly different registers).
- windenntw 2mo agoThis is called template-based compile-time programming. By making 3 instances of linear_feedback_shift_engine class template ( and 2 of xor_combine_engine ), you are forcing the compiler to expand the code exactly as-is 3 times, each with different parameters. The parameters to the template are constant, therefore the compiler can easily look at how they are used and you are guaranteed ( even in a 1999 c++ compiler ) that the compiler will look at the copies of the code and merge them as much as possible into a single piece of code... which is the one that you see when you decompile the code. So in summary, it means that you get to write fairly readable code while the final binary is fully optimized as-if you had spent the time merging all the variants as needed for the specific constants.
- scottchiefbaker 2mo ago[dead]
- N_Lens 2mo ago[flagged]
- chaz6 2mo agoI read another mention of Factorio today https://devblogs.microsoft.com/cppblog/bringing-correctly-rounded-math-to-production-with-llvm-libc/ https://devblogs.microsoft.com/cppblog/bringing-correctly-ro... It mentions how they had to use a custom math library to differences in results on different platforms causing multiplayer sync issues.
- FrustratedMonky 2mo agoIt gives me hope, that out there in the internet, there are still people just doing purely geeky deep dives. I wish you good luck in life.
- jtrn 2mo agoThis is so awesome! Thank you so much for this extremely fascinating read/work! I love combining gaming and learning!!
- renyicircle 2mo agoThe coolest part of this for me is that it's not only reverse engineering the RNG and being able to predict random rolls, which is relatively simple for that PRNG algorithm, but then being able to implement that algorithm in-game using combinator networks. There are already a lot of amazing things that you can do with combinators and this is a great example to add to the list.
- 6yyyyyy 2mo agoGames, especially multiplayer games, should start using CSPRNGs and hash functions for random events. This has in particular been a problem for Minecraft where people can reverse-engineer coordinates from screenshots of natural terrain. Most games don't need so much randomness that performance is an issue.
- Jubijub 2mo agoI can only applaud the dedication to write such a long and precise article about such a niche topic
- poppafuze 2mo agosay goodbye to that debug symbol file.