Welcome to Suricrasia Online!

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FAQ

What even is this?

Have you ever wanted to prove that you didn't know something? Now you can! You can use this technique to prove that you don't know 256 bits of information. Of course, you cannotchoose what information you don't know, it's entirely random. But it's the thought that counts, right?

How does this work?

Essentially we're taking advantage the preimage resistance of the SHA-256 hash function. Preimage resistance says that given a valueB, it's computationally intractable to find a valueA such thatB = SHA-256(A).

If we wanted to forge a "no-knowledge" proof—that is, we actually know the valueP but we want to prove that we don't—we'd be forced to reverse a SHA-256 hash. Thanks to preimage resistance, this is impossible (at least within our universe.)

If we have our finalC value then the only way to generateP is by reversing the SHA-256 hash function, which is impossible due to its preimage resistance. If we computeP first and then use it to generateC, we would still need to provideH andN, and we're back at square one. We'd need to reverse the hash valueH, which is intractable.

What's the point of this?

Novelty :3

Did you come up with this?

Nope! Credit for the idea goes to@chordowl on Twitter. I just coded up this page because it tickled my fancy.

Don't you mean zero-knowledge proof?

No, a zero-knowledge proof is something else entirely. In a zero-knowledge proof, you prove that you know something without revealing any information about what that something is. One common example is proving you've solved the three-colouring problem on a graph without revealing the actual colouring. You can find an excellent explanation of the proof process over atZero Knowledge Proofs: An illustrated primer.

Can we make a zero-knowledge no-knowledge proof?

Perhaps! There has been research into applying zero-knowledge proofs to cryptographic signatures. In these systems, your secret key is a nonce value and the public key is its hash. As part of the signature-making process, you create a zero-knowledge proof that you know the preimage to the public key. One specific scheme is called "ZKB++" and is presented in the paperPost-Quantum Zero-Knowledge and Signatures from Symmetric-Key Primitives by Chase et. al.

So given the mathematics involved with ZKB++, we could create a zero-knowledge proof that we have someH = SHA-256(N), without revealing eitherH orN. Using this system we can prove that we don't know something, without revealing any other information. Simply incredible.