So, I haven’t read up on this quantum attack stuff, and I don’t know what Kairos is referring to, but setting aside quantum computing for the moment, breaking a cryptographic hash would simply require being able to find a hash collision, finding another input to a hash function that generates the same hash. It wouldn’t require being able to reconstitute the original input that produced the hash. That collision-finding can be done – given infinite conventional computational capacity, at any rate – simply from the hash; you don’t need additional information.
So, I haven’t read up on this quantum attack stuff, and I don’t know what Kairos is referring to, but setting aside quantum computing for the moment, breaking a cryptographic hash would simply require being able to find a hash collision, finding another input to a hash function that generates the same hash. It wouldn’t require being able to reconstitute the original input that produced the hash. That collision-finding can be done – given infinite conventional computational capacity, at any rate – simply from the hash; you don’t need additional information.