What does a PGP signature on a Git commit prove?

Re:What does a PGP signature on a Git commit prove? by bawolff on Wednesday March 31, 2021 @01:31AM (#26643840)

I dont think this is true.

For a chosen prefix collision you need to be able to hide a few bytes of binary data in the file. Sometimes that is prohibitive but in most file formats that is do-able.

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Re:What does a PGP signature on a Git commit prove? by zie on Wednesday March 31, 2021 @04:07PM (#26652426)

OK, let's assume what you say is true. You spent the $100k or whatever to compute a SHA1 hash collision and you can replace the bits 11011 with the bits 1010. How is this useful? It *MIGHT* be useful, but chances are it's not very useful, as lots of data formats are pretty lossy and a random bitflip here or there doesn't matter that much.

Just because you have a SHA1 collision doesn't mean you can put any bits wherever you want and still have it be a SHA1 collision.

The really hard part is being able to flip whatever bits you want(to achieve some goal, like a RCE or whatever) AND make it a SHA1 collision. This is currently very much an open problem, nobody has been able to demonstrate(that we are aware of).

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