Smart Contract Reference

Pool Contract

The core privacy pool. Handles atomic ZK transactions (deposit, withdraw, transfer) and operator disbursements for x402 payments.

transact(proof, ext_data, sender)

Execute an atomic ZK transaction. The contract:

1. Verifies the Groth16 proof via the verifier contract
2. Checks that the Merkle root matches a stored root
3. Verifies input nullifiers are not spent, then marks them
4. Transfers USDC (direction depends on ext_amount sign)
5. Inserts output commitments into the Merkle tree

Parameters:

• proof: Groth16 proof struct (a, b, c points + public inputs)
• ext_data: External data (recipient, ext_amount, encrypted_output0, encrypted_output1)
• sender: Address that authorizes the transaction

disburse(recipient, amount)

Operator-only. Transfer USDC from pool to a registered service address. Used by the batch operator for x402 payments.

get_root() → U256

Read the current Merkle tree root. No gas cost (read-only simulate).

update_asp_membership(new_contract_id)

Admin-only. Update the ASP membership contract reference.

Groth16 Verifier Contract

Verifies Groth16 proofs on-chain using Stellar Protocol 25 BN254 host functions.

verify(proof, public_inputs) → bool

Performs the BN254 pairing check: e(A, B) = e(alpha, beta) * e(IC, gamma) * e(C, delta)

Uses native host functions: bn254_g1_add, bn254_g1_mul, bn254_pairing_check.

ASP Membership Contract

Binary Merkle tree (10 levels) for inclusion proofs.

insert_leaf(leaf) → (index, root)

Insert a new leaf. Returns the leaf index and updated root.

get_root() → U256

Current tree root.

ASP Non-Membership Contract

Sparse Merkle tree (10 levels) for exclusion proofs.

insert(key, value)

Insert or update a key-value pair.

delete(key)

Remove a key.

verify_non_membership(key, siblings) → bool

Verify that a key does NOT exist in the tree.