ZK Circuits
zkTelos uses two ZK proof circuits. Every transaction must produce valid proofs for both before the pool contract will accept it.
Transfer Verifier Circuit
Verifies that a transaction is valid — that the sender has sufficient balance and that the transaction is correctly formed — without revealing any transaction details.
Who generates this proof: The user's wallet (client-side), before submitting to the relayer.
Questions it answers:
- Does the sender have sufficient shielded balance for the transaction?
- Are the input and output notes correctly formed?
- Is the nullifier valid (preventing double-spend)?
- Do the encrypted output amounts match the claimed amounts?
The proof is generated entirely on the client side using the user's local spending key. It is never sent to the relayer or any external service — only the proof output is transmitted.
Tree Update Verifier Circuit
Verifies that the Merkle tree was updated correctly after a transaction is added.
Who generates this proof: The relayer (for normal transactions). The user if interacting with the pool directly.
Questions it answers:
- Was the new transaction subtree added at the correct position in the tree?
- Does the resulting tree root match the expected value?
Proving System
- Framework: Fawkes-Crypto — a lightweight zkSNARK framework using Groth16 and the BN254 curve
- Circuits library: libzeropool
- Client library: libzeropool-rs — Rust wrapper including Merkle tree implementation and user account/transaction building
Batch Deposit Verifier
A third verifier handles batched direct deposits from the DirectDepositQueue:
Who generates this proof: The relayer, when processing a batch of queued direct deposits.
Questions it answers:
- Were all deposits in the batch correctly applied to the Merkle tree?
- Are all deposit amounts consistent with what was queued?
Proof Verification On-Chain
All proofs are verified by dedicated Verifier contracts on Telos EVM before any state transition is accepted. See Deployed Contracts for verifier addresses.
| Proof Type | Verifier Contract |
|---|---|
| Transfer | TransferVerifier |
| Tree update | TreeUpdateVerifier |
| Batch deposit | BatchDepositVerifier |