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There was a programming competition, can't remember which, similar to IOCCC but more about problematic software? where the redaction was reversible despite bein

There was a programming competition, can't remember which, similar to IOCCC but more about problematic software? where the redaction was reversible despite being pure black, due to the format chosen allowing for left over information in the image (vastly reduced quality but it was enough to allow text to be recovered!) [edit: see replies!] There was also the Android (and iOS?) truncation issue where parts of the original image were preserved if the edited image took up less space. [edit: also see replies!] Knowing some formats have such flaws (and I'm too lazy to learn which), I think the best option I think is to replace step 6 with "screenshot the redacted image", so in effect its a completely new image based on what the redacted image looks like, not on any potential intricacies of the format et al.

ZeWaka 1y ago
There's tricks like this with embedded thumbnails.
evertedsphere 1y ago
https://www.underhanded-c.org/_page_id_17.html https://www.underhanded-c.org/_page_id_17.html
fanf2 1y ago
You are thinking of John Meacham’s winning entry in the 2008 underhanded C contest https://www.underhanded-c.org/_page_id_17.html https://www.underhanded-c.org/_page_id_17.html
- turnsout 1y ago
  Wow, it took me a minute to figure out how his entry works. You really could read that code and assume it was correct. The resulting image is perfectly redacted visually, and the missing data is not appended or hidden elsewhere in the file. You would only discover it by inspecting the PPM image in a text editor. Very sneaky!
qwertox 1y ago
Maybe you're referring to "aCropalypse". Also there was an issue once where sections with overpainted solid black color still retained the information in the alpha channel. https://www.wired.com/story/acropalyse-google-markup-windows-photo-cropping-bug https://www.wired.com/story/acropalyse-google-markup-windows... https://www.lifewire.com/acropalypse-vulnerability-shows-why-you-should-never-trust-software-redactions-7370383 https://www.lifewire.com/acropalypse-vulnerability-shows-why...
- Modified3019 1y ago
  I also recall at one point some image file format that ended up leaking sensitive info, because it had a embedded preview or compressed image, and the editing program failed to regenerate the preview after a censor attempt. Was a loooong time ago, so I don’t remember the details.
  - fullstop 1y ago
    AT&T leaked information, as did the US Attorney's Office, when they released PDFs with redacted information. To redact, they changed the background of the text to match the color of the text. You could still copy and paste the text block to reveal the original contents. https://www.cnet.com/tech/tech-industry/at-38t-leaks-sensitive-info-in-nsa-suit/ https://www.cnet.com/tech/tech-industry/at-38t-leaks-sensiti...
googlryas 1y ago
The underhanded C contest: https://www.underhanded-c.org/ https://www.underhanded-c.org/
- teddyh 1y ago
  Too bad that they only show the winners up to 2015. All the later ones are on github.com, but are harder to find.
deleted 1y ago
[deleted]
youainti 1y ago
I would guess that would be due to compression algorithms.
rkagerer 1y ago
Step 5.5) Take a new screenshot of the image.
- Calwestjobs 1y ago
  step 5.5.5 - tell chatgpt what is on image to regenerate it for you XD
Calwestjobs 1y ago
what about intentional adding data into image? screenshot - im not convinced apple does not use invisible watermark to add info into image data. but for fact every photo you take with iphone, contains invisible watermark with your "phone serial number". to remove such watermarks, facebook is converting every picture you post for last 10 years... just weird extra con to using modern technology. try to copy banknote on your printer, it will not print anything, just says error. + every page of text printed contains barely visible yellow marks containing again serial number of printer. ....

ZeWaka 1y ago

There's tricks like this with embedded thumbnails.

evertedsphere 1y ago

https://www.underhanded-c.org/_page_id_17.html https://www.underhanded-c.org/_page_id_17.html

fanf2 1y ago

You are thinking of John Meacham’s winning entry in the 2008 underhanded C contest https://www.underhanded-c.org/_page_id_17.html https://www.underhanded-c.org/_page_id_17.html

turnsout 1y ago
Wow, it took me a minute to figure out how his entry works. You really could read that code and assume it was correct. The resulting image is perfectly redacted visually, and the missing data is not appended or hidden elsewhere in the file. You would only discover it by inspecting the PPM image in a text editor. Very sneaky!

qwertox 1y ago

Maybe you're referring to "aCropalypse". Also there was an issue once where sections with overpainted solid black color still retained the information in the alpha channel. https://www.wired.com/story/acropalyse-google-markup-windows-photo-cropping-bug https://www.wired.com/story/acropalyse-google-markup-windows... https://www.lifewire.com/acropalypse-vulnerability-shows-why-you-should-never-trust-software-redactions-7370383 https://www.lifewire.com/acropalypse-vulnerability-shows-why...

Modified3019 1y ago
I also recall at one point some image file format that ended up leaking sensitive info, because it had a embedded preview or compressed image, and the editing program failed to regenerate the preview after a censor attempt. Was a loooong time ago, so I don’t remember the details.
- fullstop 1y ago
  AT&T leaked information, as did the US Attorney's Office, when they released PDFs with redacted information. To redact, they changed the background of the text to match the color of the text. You could still copy and paste the text block to reveal the original contents. https://www.cnet.com/tech/tech-industry/at-38t-leaks-sensitive-info-in-nsa-suit/ https://www.cnet.com/tech/tech-industry/at-38t-leaks-sensiti...

googlryas 1y ago

The underhanded C contest: https://www.underhanded-c.org/ https://www.underhanded-c.org/

teddyh 1y ago
Too bad that they only show the winners up to 2015. All the later ones are on github.com, but are harder to find.

deleted 1y ago

[deleted]

youainti 1y ago

I would guess that would be due to compression algorithms.

rkagerer 1y ago

Step 5.5) Take a new screenshot of the image.

Calwestjobs 1y ago
step 5.5.5 - tell chatgpt what is on image to regenerate it for you XD

Calwestjobs 1y ago

what about intentional adding data into image? screenshot - im not convinced apple does not use invisible watermark to add info into image data. but for fact every photo you take with iphone, contains invisible watermark with your "phone serial number". to remove such watermarks, facebook is converting every picture you post for last 10 years... just weird extra con to using modern technology. try to copy banknote on your printer, it will not print anything, just says error. + every page of text printed contains barely visible yellow marks containing again serial number of printer. ....