- U.S AT DEFCON 2 APRIL 2017 HOW TO
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- U.S AT DEFCON 2 APRIL 2017 SOFTWARE
These near-collision blocks also cause the PDF to display a first JPEG image in one case, and another JPEG image in the second case. However, the main idea consists of inserting specific near-collision blocks in the middle of the files to manipulate the hash result. I'll keep this part very short, as it's better to follow the slides or the video. This tool is being run for each commit at Github, for example. Meanwhile, a tool has been created that detects potential collisions. Git intends to move away from SHA1, but this will take some time.
In the past, we have seen clever malware use MD5 collisions on an X.509 certificate (see Flame). The authors showed this has an impact on: Once this is done, the tool just re-uses the work to use the right blocks and adjust to the input, and that's very quick. If it's so easy to generate a collision, why did it take the authors so long to compute one, you might ask? Their research was long because they had to find the right file prefix and collision blocks. Note that the tool takes as input two PDFs, and generates as output two other PDFs, which display like the originals but produce a SHA1 collision. These documents are clearly very different. See the screenshot below of two obviously different PDFs: Proof? I generated one myself in a few seconds using this tool. It is very easy to generate colliding PDF documents. For more on this, see Wikipedia or slides 7 to 9 from their presentation. I just intend to clarify the differences between a collision attack (which is what they have), and first or second pre-image attacks. I am absolutely not trying to downplay their attack.
U.S AT DEFCON 2 APRIL 2017 HOW TO
Rather, what they do is create another document that looks like yours and for which they know how to create a collision. But even if you supply a PDF document, they can't create a collision (except for a few lucky exceptions) with your exact document. First of all because, so far, their collision only works for PDF documents. So, if you provide them with a given document of your own, they most probably won't be able to craft a collision. This does not work with any document, but only with documents they specifically make themselves for this attack. The authors were able to craft two documents that hash the same with SHA1. I'm going to try to summarize the main points here. After listening to it, I decided it was not just great, it was EXCEPTIONAL. With the nickname "Crypto Girl", I obviously had to listen to this talk, and I initially thought it would be great.
U.S AT DEFCON 2 APRIL 2017 SOFTWARE
July was very busy with the annual DEFCON and BlackHat US conferences, but also RMLL, the Worldwide Free Software Meeting held this year in France.Įlie Burzstein et al, How We Created the First SHA-1 collision and what it means for hash security video, DEFCON 25 and paper
Welcome back to our monthly review of some of the most interesting security research publications.
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