A party A gives me a commitment of a message $m$ and want to convince B that is $|m|=L$. The proof myst be:
- Non-interactive (a prover can convince me by sending me one message)
- Succint (constant or sublinear size in the length of m)
I was looking into the NIZK space but I could not think of any solution.
Note: I have a candidate which however, it really is an overkill:
Create a SNARK proof that proves the witness: $m$ such that length is $L$ and hash is $H(m)$, where $H$ is a cryptographic hash function and $H(m)$ is public knowledge (so verifier knows)