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.
Comments
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.