#Reversible computing

[foone]

Have you heard about the Polish Train company, Newag, and the bullshit it turns out they got up to?

So, the regional rail operator Koleje Dolnośląskie bought some Newag Impuls back in 2016 . In late 2021, some of them need to have major maintenance done, as they've been in service a while. So the company SPS (Serwis Pojazdów Szynowych) gets the contract to fix them. They basically take the train apart, replace a bunch of it, following all the rules in the documentation Newag gave them, and... it won't move. The train says everything is fine, the brakes are off, there's plenty of power, but you push the throttle up and it won't move.

SPS spends a while trying to figure out what the fuck is wrong, with no luck. So they hire some hackers from the Polish security group Dragon Sector. Dragon Sector figures out how to get into the code of the computer system that runs the train, and OH MY GOD.

So it turns out there's a secret train-lock system. If it's on, the train won't move. This will be triggered in some situations you might think are normal: the clocks are wrong, the serial numbers of the various parts have changed, and a firmware mismatch between the main computer and the power system. Now, the fact that it makes sense to not run the train in these situations until someone can check it? that doesn't extend to the fact the train uses a SECRET lock system, rather than just popping up an error message telling you what's wrong. There's also the problem that while these are all potential error problems, they can't be cleared by anyone with the technical manuals, which are supposed to cover everything about how to run these trains. Only Newag themselves can reset this system.

Which, you know, keeps SPS from properly fixing them. Only Newag can fix them now, but not because SPS lacks any technical ability, but because Newag sabotaged their own trains. But don't worry: it gets worse.

So now that Dragon Sector knows what's happening, they get to look at other trains. It turns out the trains aren't all running the same software, and there are other tricks in there.

One of them is a "how long has the train been stopped?" check. If the train hasn't hit 60 km/h in 10 days, the train locks itself and won't move until Newag can clear it. So, like, if a train is ever out of service, like it's going to a repair place... it'll break itself. Unless the repair place is owned by Newag.

But two of the trains go further: See, these trains have GPS built in, right? You may be able to guess where this is going...

THEY JUST MAKE THE TRAIN CHECK IF IT IS PARKED AT THEIR COMPETITORS' REPAIR YARD AND BREAK ITSELF IF IT WAS.

The sheer audacity of this move. This is frighteningly bullshit anti-competition self-sabotage.

This has, obviously, made some parts of the Polish government to start investigating this. Newag may be (and hopefully will be) in a lot of trouble.

For more info, there's a great video of a presentation by the three people from Dragon Sector who did the hacking, which was presented at the 37th Chaos Communication Congress in Germany.

Ars Technica also has an article on it, but it predates the presentation so it doesn't have some of the later details.

Anyway, the good news is that in the end the hackers at Dragon Sector were able to unlock most of the trains: A few had additional trickery that they didn't want to hack around, because it might break the train's certification. For the others, they discovered undocumented "cheat codes" in the software that they could use to bypass the secret lockouts... presumably the same ones that Newag would have used when they "repaired" trains.

[itsstilltru]

something something

[tilde-he]

Cool! I tried to work out how gradient descent could be done with as few auxiliary bits as possible, but none of the things I tried worked. But I only tried a couple things.

But also, hm, if the gradient descent step is reversible, then it has to preserve volume (or, I guess just cardinality, as the numbers have finite bit depth), which seems like an obstacle if we want to end up in the region where the loss is low.

I guess if we define a probability distribution in terms of the loss, as like a Boltzmann distribution type thing, then maybe some kind of, “the number of auxiliary bits spent/erased corresponding to the difference between the uniform distribution and the distribution obtained from the loss function”? I think I saw a video claiming something similar about the distribution learned (rather than a distribution over possible parameters), but the argument I saw seemed unclear.

Ah, if we treat loss as like potential energy, then if instead of plain gradient descent, gradient descent with momentum is used, in a way such that energy is conserved, then that seems like it could be nice and reversible. It is in the continuum limit at least (assuming the loss is smooth) and I would imagine it could be made to be reversible when using discrete time-steps and finite bit depth as well. In the continuous limit at least the energy would be conserved, and probably also if things are set up for the process to be reversible in the discrete case? Then, maybe bits could be spent on decreasing the kinetic energy when the potential energy (the loss) is low? Is there some optimal way to do this?

If we want out computation to start in some initial configuration which may-as-well-be random among N possible states as far as it relates to final answers we want, and we want it to end up in one of M states (with M < N), then by the generalized pigeonhole principle, at least 1 of the M desired final states is reached when starting with at least (N/M) of the starting states, and so this requires spending log_2(N/M) bits to encode the information of which starting state was used.

So, for the size M of the set of configurations that are good enough, hm…

So if M/N is the fraction of the possible states which have loss less than some quantity… we only want to spend a bit if it will decrease the size of the set of “all points with loss less than or equal to the largest loss we could end up at” by half I guess? Uhhh idk how we would determine that though..

New piece on a new startup in a new venue:

[gothducky]

Anyone else excited for Reverse1999? :-)

[r477m4n-wh34713y]

[im-kinno-hello]

and if i made a comic about them making a blog for the weird demon dog they found in the woods just because they are being brainwashed by it and it told them they need to spread the word of what word they don’t even fucking know?

[cheemken]

Tooth Fairy third wheeling Vila and Windsong is the funniest fucking shit can you imagine drinking hot chocolate while those two are casually flirting and giving each other bedroom eyes as they sit beside the hearth, flirting as if you're not there w them and can hear every sinful whisper they tell each other, girl I'd crash out lmfao

[hammerhead-jpg]

Very overdue fool! Gavin

Heeheehaahhaa

[meamiki]

[reverse entry AU]

so glad the work week is over!

no more meetings!

what do you mean its only tuesday.

[modpollyblog]

chimera has posted a pride image of his fursona. i am going to identify the terms like i did with his meteorcare/clovercare pride images because the full extent of how gross it is that someone identifies this way and is proud of it is indescribable. image and terms will be under the cut in case anyone doesn't want to see it.

loligender - underage/prepubescent girl character gender (flag by his fiance, Loki)

intoxiphilia - intoxication fetish

hyperromantic - unwanted and/or excessive feelings of romantic attraction

agefluid - a transage term for someone whose internal age changes over time (the specific flag he chose for this is not a radqueer/transage term! he stole a did/osdd system flag!)

masochism - being hurt/pain fetish

hemaetophilia - blood fetish

fictomap (fictional pedophilia) - attraction to fictional children/child characters in media

automap (autopedophile) - fetish for imagining yourself as a child being abused by a pedophile

autozoo (autozoophile) - fetish for imagining yourself as an animal being abused by a zoophile

hypersexual - unwanted and/or excessive feelings of sexual attraction/arousal

faggot - reclamation of a slur usually aimed at feminine gay men

genderfluid - a gender identity that changes over time

pomogender - a gender that doesn't want to be labeled/cannot fit any existing labels

xenogender - a gender spectrum that goes beyond the normal human understanding of gender (concepts, animals, plants, etc.)

pup play - i can't sum puppy play up into one sentence. here's the wikipedia page for it if you're interested. it is generally a kink/bdsm/leather thing, but not always. important to note that it is not bestiality/zoophilia.

apprentipawage - a transage label made by his fiance (Loki) where your age relates to being a kitten from warrior cats

fictophilia - attraction to fictional characters

transmasc - transmasculine

incestophilia - attraction to incest

kindivergent - a label made by Kittycorn, attraction to found family members

pupgender - a gender related to puppies and/or dogs

shotagender - underage/prepubescent boy character gender (flag by his fiance, Loki)

somnophilia - sleep fetish

vore - vore fetish. i'm not defining vore i don't care

transage - an identity where your internal (intra) age doesn't match your real/chronological (chrono) age. transage is heavily used by radqueers/transid/maps (pedophiles), while the term chronosian is generally used by did/osdd system members, people who are neurodivergent, or people with trauma/brain damage.

kodocon - attraction to underage/prepubescent characters of all genders (girls/loli, boys/shota, nonbinary/crona/nana)

aegosexual - an identity where there is a disconnect between yourself and arousal. usually the person likes the idea of sex, but doesn't want to participate.

pansexual - attraction to people regardless of gender

[itsstilltru]

I finally did it ~ AM and Ted reverse au

I’m so proud of AM’s suit

I just love this shot like wtf I drew a slightly angled pov???

Bonus sketches

[xxplastic-cubexx]

they bubbled my boy.. sadly i do not know where this is from though reverse image search would probably do the job

They bubbled my boy …

[X-Men/Fantastic Four (2020) #1]

[thetooncrew]

they should get a story together sometime

[fishareglorious]

Some have suggested I should spend my vacation "like a human", so I have prepared several options. People seem to like this one the most. You refused. I see. You must prefer the Thomas the Tank Engine face. - Lucy's lobby interaction

THOMAS THE TANK ENGINE FACE???????????!?!?!?!?!??

[humlase]

Nothing is worse than the consequences of my own actions.

[cas-azul]

After much pain, suffering, and agony, I finally managed to draw digitally again, after years. Unfortunately, the computer I use for drawing is older than dinosaurs... but I did it!

Finally, I was able to draw a picture for the first chapter of my fic, "blue butterfly."

...run Will, run!

Below, I will leave the process and sketches.

___________

Luego de mucho dolor sufrimiento y agonía finalmente pude volver a dibujar en digital, luego de años, lamentablemente mi computadora que uso para dibujar es más vieja que los dinosaurios...pero lo logre!

Finalmente pude hacer un dibujo del primer capítulo de mi fic, "mariposa azul"

¡...corre Will, corre!

Abajo dejaré el proceso y bocetos.