Here's the problem I'm trying to solve:
yis public, it's a timestamp
- there is A who knows
x- it's a file
- A can send B some information about the file (a hash?), but not the full file (it's too big)
- A then sends the file
The role of B now, is to periodically verify that at given time
y C still has the file
x. C could send something like
hash(x, y) to B, and B (who doesn't have the full
x) needs a way to verify that C indeed has the full file
x at time
Here's the original question I've asked (it includes the solution approach I've been trying to take):
Say I only know hash(x) and y.
I receive z that is supposed to be hash(x + y)? Is there any way I can verify that without knowing x?
I'm interested in any mechanism that could make such check possible rather than particular hash and + operations.