>Is this an argument against hash trees? Can you explain more about the this potential attack? It seems to be to be equivalently hard to finding preimages.
If you only have to rehash a branch as apoosed to the entire tree and match hash's then you have a easier time as it is alot faster by design.
Now if the way the hashing work is that only say 1234567 will get the hash value 11 and no other variation then i will have no issues and welcome this as a great achievement and pure brilliance. But I dont feel this is the case and nor could it be by reducing any large amount of entropy into a shorter definition and that is what a hash function does after all and one hash value will match more than the original data.
Actualy if you pick the block to paralise striped (ie 100 bytes and block 1 is every 10th byte so byte 1,11,21,31... and block 2 is 2,12,22,32....) then the ability to modify the code/data in any nefarious means would be as hard (if not harder ) than having to rehash the entire lot.
The only issue with this approach of blocking is that it works on all the data and as such would for example be no use for streaming which is a terrable exmaple but you get the idea.
If you only have to rehash a branch as apoosed to the entire tree and match hash's then you have a easier time as it is alot faster by design.
Now if the way the hashing work is that only say 1234567 will get the hash value 11 and no other variation then i will have no issues and welcome this as a great achievement and pure brilliance. But I dont feel this is the case and nor could it be by reducing any large amount of entropy into a shorter definition and that is what a hash function does after all and one hash value will match more than the original data.