How Zero-Knowledge Proofs Work
A simple explanation of the cryptography that powers private transactions on Senddy.
Zero-knowledge proofs sound like science fiction: a way to prove something is true without revealing any information about it. But they're real, mathematically proven, and they're the technology that makes Senddy possible.
In this post, we'll explain how zero-knowledge proofs work in plain language—no math degree required.
The Classic Example
Imagine you have a color-blind friend, and you want to prove to them that two balls are different colors (one red, one green) without telling them which is which.
Here's how you could do it: Your friend holds the balls behind their back and either switches them or keeps them the same. Then they show you the balls and ask, "Did I switch them?"
If the balls were actually the same color, you'd have to guess—50% chance of being right. But since they're different colors, you can always tell whether they were switched.
If you repeat this test 100 times and get it right every time, your friend becomes convinced the balls are different colors. You've proven the statement without ever revealing which ball is which color.
This is the essence of a zero-knowledge proof: convincing someone that something is true without revealing the underlying information.
How Senddy Uses Zero-Knowledge Proofs
When you send money on Senddy, you need to prove several things:
You own the funds you're spending (authentication)
You have enough to cover the transaction (sufficient balance)
You haven't already spent these funds (no double-spending)
Normally, proving these things would require revealing your balance and transaction history. But with zero-knowledge proofs, we can verify all of this without exposing any sensitive information.
The Technical Bit (Simplified)
A zero-knowledge proof is like a very complicated lock and key system. The "lock" is a mathematical statement about your transaction. The "key" is a proof that the statement is true.
When you make a transaction, your device generates a proof using your private data (your balance, your spending history). This proof is then verified without learning the underlying private inputs.
Why This Matters
Before zero-knowledge proofs, privacy and transparency were seen as opposites. You could have a transparent system where everything was verifiable, or a private system where you had to trust someone.
Zero-knowledge proofs break this tradeoff. Senddy can be fully auditable—every transaction is cryptographically verified—while keeping the contents of those transactions completely private.
The State of the Art
At Senddy, we use Noir circuits with UltraHonk proofs generated on your device. An attestation service verifies those proofs so on-chain settlement stays cheap and fast — typically a few seconds for a private transfer. Unlike Groth16 systems, UltraHonk does not require a per-circuit trusted setup.
Looking Ahead
We're still early in the zero-knowledge revolution. Researchers are developing new techniques that are faster, cheaper, and more flexible.
At Senddy, we're proud to be building on this foundation. The math is complex, but the result is simple: your money, your business.