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David Buchanan


Sep 23

7 tweets

The image in this tweet displays its own MD5 hash. You can download and hash it yourself, and it should still match - 1337e2ef42b9bee8de06a4d223a51337 I think this is the first PNG/MD5 hashquine.

badidea 🪐


Aug 09 13View on Twitter

Trick I want to see: a document in a conventional format (such as PDF) which mentions its own MD5 or SHA1 hash in the text and is right

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This was particularly tricky to make work because the image data in a PNG needs to have a valid adler32 checksum, *and* a valid crc32 checksum. Each hex digit "pixel" needed its own colliding block, generated with UniColl. There are 448 of them, taking over 24h to compute.

The adler32 checksum was collided to a chosen value using 48 FastColl collisions, with a meet-in-the-middle technique. After the adler32, the crc32 was collided similarly, using another 48 FastColl blocks. As the name suggests FastColl is fast, and this part only took ~minutes.

UniColl:… FastColl:…

Contribute to brimstone/fastcoll development by creating an account on GitHub.…

GitHub - brimstone/fastcoll

See also: a GIF hashquine…

played around with this a bit, here is an animated gif displaying its md5sum:

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Here's a behind-the-scenes look at what the collision data looks like. You can't see the garbage pixels in the final image because I used a clever palette. Right column is the main set of UniColl collisions, and the lower edge is the adler32 FastColl blocks.

More hashquine goodies:…

ICYDK the issue 0x14 of PoC or GTFO has articles about PostScript, GIF, PDF and NES (code) hashquines by @greg, @spq , @Mako, @Evan Sultanik and @Evan Teran.… The issue itself is a PDF/NES hashquine.

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David Buchanan


Reverse Engineering, cryptography, exploits, hardware, file formats, and generally giving computers a hard time. Occasional CTF player. Fedi:

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