# Zero Knowledge proofs of knowledge

Is there Zero Knowledge Proof of Knowledge protocol for Hash function? (If h(v)=w) without revealing v to the anyone can we prove that we know 'v')

• Every function in NP has zkp I think.
– VS.
Commented Apr 21, 2020 at 11:55

## 1 Answer

Yes. The simplest way to understand this is to understand the zero-knowledge proof that you know a 3-coloring of a graph. 3-coloring is NP-complete, so an arbitrary hash function $$h$$ and target value $$w$$ can be represented as a graph where knowing a 3-coloring for that graph is equivalent to knowing a $$v$$ such that $$h(v) = w$$.

That isn't the most efficient way to do it; for that you'd want zk-snarks or one of the zillion similar encodings. That approach is similar but you're modeling your hash function as a modular matrix multiplication instead of a graph coloring. But the answer is yes, there is a zero-knowledge protocol for proving you know the preimage of a value for a hash function.

• Can u be more precise that how zk-snarks is useful here? I do not mean internal working. but how the input to the zk-snarks and output to the zk-snarks look like Commented Jul 21, 2020 at 19:08