# Prove the size of a message in a succinct way

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)

• Your question is not well defined. Is the message encrypted, is it committed? How? – Yehuda Lindell Apr 25 '17 at 12:03
• @YehudaLindell I just updated the question – graphtheory92 Apr 26 '17 at 22:04