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Re:Updating the Git protocol for SHA-256 by eknkc on Saturday June 20, 2020 @03:37AM (#23582457)
This makes sense. However the implementation detail of h_0(x) could also be foo(x) + bar(x) or whatever. At the end, you have a function that returns a fixed number of bytes.

I doubt any has function that we use today changes the algorithm halfway through its operation though. So your proposal might have a benefit in security by obscurity way.

Re:Updating the Git protocol for SHA-256 by qwename on Saturday June 20, 2020 @04:00AM (#23582536)
I suppose I missed the assumption that h_0, h_1 and h_2 cannot be trivially decomposed into concatenations of other hash functions, whereas h_3 and h_4 can.

Also, there's no obscurity since h_1 and h_2 are the actual targeted hash functions, h_3 and h_4 are just to show that concatenation doesn't change the actual problem or make it harder.