Question: Disregarding brute-force, is it any easier to calculate a partial hash collision, in which only a certain number of bits match?
Reasoning: On many websites you find hashes for file downloads. That's nice for integrity checks from the original website, and very nice when downloading from mirrors to verify that the file wasn't changed.
I just put up a new file download to a website and added the SHA256 hash as well. Checking it, I noticed that I didn't really pay attention to the full hash, and that I never do. Instead I usually look at the first few digits and the last few digits, and disregard most of the values in between, thinking if those match, the others probably will as well.
No I ask myself, if that is a potential "social" attack vector. Offer a manipulated download of a file that just matches the partial checksum.
Calculating a full hash collision of SHA256 has not been demonstrated as far as I know. So this boils down to the question, if from the mathematical side it is any easier to calculate a partial hash collision for SHA256, preferably at certain bit locations at the front and back?
Let's consider brute-force still too expensive, since that will of course get easier with less and less bits to come out correct.