On Thursday, 15 September 2016 at 10:13:47 UTC, cym13 wrote:
DoS by collision attack are a form of preimage. The idea is to generate intentional collisions to force heavy computations on serveur side. It only works if finding collisions many collisions for the same hash is cheap which is directly linked to the ability to find a value that gives a given hash (although it doesn't have to be easy to find any hash).
As a counterexample, collision attacks on MD5 are cheap and practical, but preimage attacks are still theoretical.
Self-plug, but I wrote a bit more about hash function attacks a little while back:
https://theartofmachinery.com/2016/01/03/what_difference_can_order_make_when_hashing.html
