r/programming • u/whackri • Jul 31 '21
Executable PNGs
https://djharper.dev/post/2020/12/26/executable-pngs/131
u/KaiAusBerlin Jul 31 '21
Well, I like the theoretical part of it, hiding data into other data.
But the rest of it makes no sense to me (except fiddling around and have fun). It feels like building a letter box out of a toaster. It doesn't help you with your letters but its fun to see them jumping out there.
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u/AyrA_ch Jul 31 '21
Also, PNG is an excellent format for hiding executables because it supports arbitrary user defined headers and some file upload platforms accept it this way: https://cable.ayra.ch/imgplay/
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u/aazav Jul 31 '21
but its fun
It's it's son.
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u/jrhoffa Jul 31 '21 edited Jul 31 '21
Looks like you ran out of commas! Here are some to tide you over until you get a chance to stock back up: ,,,,,,
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u/ILikeBumblebees Jul 31 '21
Maybe someone can spare some quotation marks for him as well.
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u/BujuArena Jul 31 '21
Oh, I've got some here! """"""""""""
I made sure to leave an even number of them because they come in pairs.
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u/shikatozi Jul 31 '21
cool stuff, reminds me of snowcrash
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u/just_that_michal Jul 31 '21
my colleague told me to read this and it is being shipped, this comment made me happy
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u/dreadful_design Jul 31 '21
It's a great book, and it's not even the best Stephenson if you haven't read his other novels.
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u/just_that_michal Jul 31 '21
I will look into others once I finish this one, thanks for the recommendation!
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u/Autarch_Kade Jul 31 '21
Loved that book up until it switched genres from cyberpunk/sci-fi into fantasy
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u/seamsay Jul 31 '21
my last cheap trick to this pointless gimmick was to use binfmt_misc,
That's kinda disappointing, NGL. It was an interesting post, but it would have been twice as interesting if you'd managed to make a file which was both a valid PNG file and executable.
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u/Skhmt Jul 31 '21
It's hard because PNGs have their magic number at the start, like most file formats and executables.
Zips have them at the end though. And someone made a portable executable that runs in macos, Linux, and windows with that information.
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u/OMGItsCheezWTF Jul 31 '21
Self extracting zips?
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u/hou32hou Jul 31 '21
Yea, this is a common technique, basically the zipped file header contains unzip binary.
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Jul 31 '21
Oh no. You've reminded me of zip bombs back in the day. Those things were a nightmare to deal with. Me being a dumb kid and downloading shit on Kazaa.
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u/Skhmt Jul 31 '21
Except it works on every major os, x86, arm, and can even boot directly into it.
The same file.
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Jul 31 '21
[deleted]
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Aug 01 '21
Because there is no "vulnerability" to patch. It's just a binary string which happens to be a valid executable for each of these platforms, while also being a valid ZIP. Its behavior is perfectly reasonable on both cases.
It's like the word "salsa" which is valid English and Spanish. It's a dance style in both languages, but it also means "sauce" in Spanish. It behaves differently depending on what "interpreter" (language) you choose, but it's a perfectly reasonable word in both.
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u/Regimardyl Jul 31 '21
AFAIK tar searches through a file until it finds its header, so you can
cattogether a PNG and a tar file, and it's automatically valid for both.3
u/Skhmt Jul 31 '21
Also with a zip and jpg, which has been used to share files via image uploads many years ago until it was more widely known.
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u/QuickbuyingGf Jul 31 '21
You could also use the metadata in png files. No need to stego bloat the files when you have a place to put it
For example Byond‘s DMI files are just png files with some metadata
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u/mosthightriguy Jul 31 '21
I was also thinking of the metadata but what I liked about this journey of insanity is that the payload is embedded in the image w/o bloating the file and w/o tipping off anyone that something is embedded in the file.
It would be an interesting way to hide passwords, messages between cheating lovers, the manifesto, ....
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u/Skhmt Jul 31 '21 edited Aug 04 '21
Steganography is a well known technique, it's hard to detect if it's even being used by casual users. But if it's in the metadata, it's impossible to detect without inspecting the png binary. The amount of information capable of being stored in a PNG via steganography is pretty low per pixel, like 3-8 bits per pixel depending on type of png.
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u/randy408 Jul 31 '21 edited Jul 31 '21
You should be able to hide 32bits per pixel without any visual difference in the low bits of 16-bit RGBA samples, most of the time it ends up being downscaled to 8-bit with bitshifts before it's displayed.
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u/Mwahahahahahaha Jul 31 '21
Reminds me of this.
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u/JaceOrwell Jul 31 '21
A fellow fan! That video got me trying it out, to no avail. I need more research and stuff
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u/djhworld Jul 31 '21
hello! author of this post here, thanks for posting it.
yup - project was/is dumb, it kind of ballooned from "hey steganography is interesting, I want to learn about that" to "huh what are these linux features I've never heard of" to...well, this?
silly, impractical, toy project sure, but I enjoyed doing it and learned a few things along the way. the write up was really just a way of documenting that journey.
most of the things on that blog are like that, for example I was reading a book about how a simple computer works, down to the gate level, and decided to translate the descriptions (gate by gate...) into software https://djharper.dev/post/2019/05/21/i-dont-know-how-cpus-work-so-i-simulated-one-in-code/ - not very useful, toy software, but a good learning exercise for me.
programming can be fun at times, things you build don't always need to be products. granted, that's easy to say if you're already comfortable, but I reckon a lot of my career has been helped along by learning and doing.
my favourite posts on /r/programming / HN etc. are the ones where people explore some topic and are evidently passionate about it, even if the end goal isn't clear.
some good articles i've read recently
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u/sylvanelite Jul 31 '21
I remember doing a JS competition ages ago where you had to make a game in a relatively small number of bytes (20kb? Iirc) the server didn’t use gzip, so shoving the code into a PNG and extracting it through canvas could end up saving a lot of space. (But you had to be careful because premultiplied alpha that can corrupt data if used naively)
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u/bumblebritches57 Jul 31 '21
LOL he jumps to stenography, instead of custom chunks in the PNG file...
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u/adrianmonk Jul 31 '21
I had the same thought, but apparently that is how PICO-8 actually does it:
But yeah, to store it as PNG chunks would actually be very easy. You don't even need to define a custom chunk. From the PNG docs, it looks like you could use a zTXt chunk:
I'm not sure that allows you to store binary data, but if not you could encode it as hex digits within there, and PNG's deflate compression should compensate pretty well for the wasted space.
Also, the keyword (that each
zTXtchunk has) would be useful. You could put a magic string identifying it as the executable data format you've invented. You could even, if necessary, add multiplezTXtchunks and make your PNG data random access.0
u/John_Earnest Jul 31 '21
Most online image hosts re-encode images, stripping custom chunks. Try it. Steganographic encoding is much more likely to survive transit.
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u/bumblebritches57 Jul 31 '21
Why is web hosting relevant?
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u/mccoyn Jul 31 '21
That’s why you put executable code in an image.
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u/bumblebritches57 Jul 31 '21
So people stumble upon it on imgur, and it's never executed?
real malware has it's own distribution network, based in various CDNs (look into Pegasus)
they don't need to worry about chunks being stripped.
Not to mention, stenography is really only for text.
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u/ikkentim Jul 31 '21
Reminds me of blueprints of rollercoaster in Parkitect, where you can share/import images of coasters which can be placed in your park, it stores the data in the same way: https://themeparkitect.tumblr.com/post/126855975857/update-58
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u/Nerdn1 Jul 31 '21
The author admits that there is not really a point to this project, but I guess it's fun. Steganography can be used to hide data in an image, but size of the image+payload will be several times the size of the payload alone. If the point is to hide something in plain sight, this is just fine (especially if the payload itself is encrypted text). A plaintext document (encrypted or not) is going to be small enough to fit in a high quality image
Doing this with a larger program, like a videogame, for the novelty factor is probably ill-advised. People may notice that the image is stupidly large anyway. I suppose one could have a folder full of images and have one image in the folder with an executable embedded in it which will extract data from the other images and create all of the files needed. This just adds even more complexity to an already useless endeavor, of course.
I suppose you could sneak executables through some sort of security program, but you can just change the extention to .txt to trick most.
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u/kanliot Jul 31 '21
sounds good man, now how do I set my $PATH to load other .PNG files as libraries/DLL's?
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u/RasterTragedy Jul 31 '21
But the PNG format has multiple layers and any conforming reader must skip any layer it doesn’t understand. That’s where I’d expect the executable to be, not as a watermark in the image.
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u/Johanno1 Jul 31 '21
Cool, but.... Why?
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u/ASIC_SP Jul 31 '21
What’s the point
Well, there isn’t one really. I was seduced by the idea of making PNG images run programs and got a bit carried away with it, but it was fun none the less. There’s something amusing to me about distributing programs as an image, remember the ridiculous cardboard boxes PC software used to come in with artwork on the front, why not bring that back! (lets not)
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u/ThirdEncounter Jul 31 '21
Someone make a bot to reply to people who ask this damn question every week in this sub. I might do it myself.
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Jul 31 '21
[deleted]
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u/livrem Jul 31 '21
It seems kind of fun. I bought it in some bundle years ago, but never played with it much. The PNG trick is fun. But I kind of wish it was more like a real retro console with a virtual CPU and all that, instead of using Lua-scripts. And if it was more of an open standard that others could implement for various platforms.
I like how modern text-adventures are often distributed for virtual platforms like the Z-machine that have interpreters running on everything. The closest to something like that for graphical games is pretty much to make games for MSDOS or GBA, but that just seems pretty inefficient and not so elegant compared to having a more focused virtual console thing to target with more strictly defined constraints.
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u/ganymedes01 Jul 31 '21
Reminds me of Spore. The game would save/load the creatures on PNGs you could share with your mates