# Bulletproofs range proof of value provided from trusted third party

I'm really interested in range proofs, and bulletproof seems to be the most effective range proof.

I saw an example of usage of bulletproofs range proof: You can generate a proof that your age is greater than 18 without revealing your exact age.

That sounds cool, but what I don't understand is how I can prove that my age is verified. Say I'm 12, but while I generate a proof, I pretend that I'm 20 and generate a proof for 20 years. Clearly, I need a third trusted party to verify that my age is really greater than 18. How it can be done?

Maybe I should generate a proof, and then a trusted third party - for example my government - signs that it to make it a valid proof? Is there a better approach?

• Talking about proofs: please proof read your question before posting. I'm pretty sure a spelling check should show up that "reaviling" is "realy" not a word, even if you don't. – Maarten Bodewes Apr 15 '19 at 12:11

I think the example that you saw was just a simple example of how a range proof would work in theory.

Range proofs could be used for encrypting transactions in cryptocurrencies, specifically the amount of the transaction.

A very simplified mathematical notation would look like this:

$$\text{E}(a) - \text{E}(b) = 0$$

where $$a$$ is the amount of coins you "spend" and $$b$$ is the amount the receiver gets. $$\text{E}$$ indicates that the values are encrypted. This simple calculation here only indicates, that $$a$$ and $$b$$ are equal, so you didn't somehow create coins out of thin air.

Bulletproofs are a new addition to range proofs, they basically prove the same thing but bulletproofs can prove something with less overhead than a normal range proof, which again makes them desirable for cryptocurrencies. You can find more information in this PDF of the published paper.