You are correct that there is no such single hash; there can't be without it being longer, because then the parts could be brute forced separately. However, a

You are correct that there is no such single hash; there can't be without it being longer, because then the parts could be brute forced separately. However, a second hash of 10% of the file would work fine. You can even truncate it if saving a few bytes is that important (since you will check the full file hash later), although I suspect even a page with a bunch of downloads would be fine with a couple of extra hashes per file. While most APIs don't expose this possibility, most hash algorithms can spit out the full hash of the file up to any intermediary points with very little additional work. Or there could be seperate hashes for different blocks of data like P2P protocols do and store them all in a separate file on the https site. However, the main issue is that these days it is very easy to just use https, most likely easier than any other solution. Browsers encouraging people to care by showing warnings should be very helpful in increasing the number of sites using https.