Offshift Dev Update, Early September 2021: Range Proofs

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Offshift is working with Zokyo to develop the platform that will finally bring private finance, or PriFi, live.

Here’s a progress update for early September, 2021.

Zokyo continues to work on the cryptography for Offshift’s platform, specifically range proof generation and verification for shielding deposits and withdrawals.

A zero-knowledge range proof is a proof that allows us to verify that a secret is in a certain range without revealing it. Range proofs allow us to check that hidden values are correct. You might remember that we first mentioned using range proofs in the Offshift Yellowpaper, where we discussed how Bulletproofs work.

Let’s look at an example that reveals the need for range proofs:

Alice wants to transfer some hidden tokens to Bob. She has two commitments associated with her account:

E = Com(10) and F = Com(2)

Then she decides to cheat the protocol and send Bob the commitments:

I = Com(112) and J = Com(-100)

This transaction is considered correct because – thanks to the homomorphism of Pedersen commitments – we can check that the sum of spent amounts is equal to the sum that was transferred:

10 + 2 = 112 + (-100), so E + F = I + J

But, (-100) is an incorrect amount of tokens, and the use of range proofs is extremely useful for this case because it allows us to check that the hidden amount is more than 0.

This means that tokens can’t appear from nowhere, and no one can cheat the protocol. Moreover, there is no need to reveal the hidden amounts, so they remain confidential.

Over the course of September, Zokyo will continue working on cryptographic implementations. You can always check out our Roadmap for a general overview as well.

If you’d like to learn more about our development with Zokyo, tune into the Offshift Developer Community Calls on the last Thursday of every month at 12PM ET! Join our Discord to listen in and chat more with our community.

To learn more and get involved, visit the links below:

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