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Unlink is a smart contract deployed on the blockchain itself. There is no bridge and no separate chain. The SDK generates the zero-knowledge proofs and signs the operations. From a builder’s perspective you call depositWithApproval(), transfer(), withdraw(), and execute(). Balances inside the contract are held as a set of encrypted UTXO notes, and every private operation is proven with a Groth16 zero-knowledge proof. The contract verifies the proof without learning the sender, recipient, or amount of a private transfer.

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The flow

  1. Deposit moves ERC-20 tokens from a public EVM wallet into the Unlink contract, creating a private balance for a unlink1 account.
  2. Transfer moves value privately between unlink1 accounts. Sender, recipient, and amount are hidden by the proof.
  3. Withdraw moves tokens back out of the contract to any public EVM address.
  4. Execute spends a private balance in external EVM calls, such as a DeFi action, and can return the result to a private balance.
The Introduction shows a diagram of this flow.

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What’s private, what’s public

DepositTransferWithdrawExecute
AmountPublicPrivatePublicPublic
SenderPublicPrivatePrivatePrivate
RecipientPrivatePrivatePublicPublic
Token typePublicPrivatePublicPublic
A deposit reveals who funded which unlink1 account and how much. A withdrawal reveals the destination address and amount, but not which private account funded it. execute() has the same exposure as a withdrawal: the on-chain calls, amounts, and target contracts are public, while the private account that funded them stays hidden, and any tokens returned with deposit-back are private again. Only transfers between unlink1 accounts hide all four properties. Plan your deposit and withdrawal amounts and timing accordingly. The private payment tutorial walks through a flow that minimizes linkability.

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Who pays gas

How gas is paid depends on the operation.
OperationWho pays gas
DepositThe user, from their EVM wallet
Transfer, withdrawUnlink, which relays the transaction for the user
ExecuteUnlink’s paymaster, which sponsors the operation
A deposit is a normal on-chain transaction sent from the user’s EVM wallet, so that wallet needs native gas. Transfers and withdrawals are submitted by Unlink’s relayer, and execute() runs as a sponsored ERC-4337 UserOperation (see Execute). The user needs no native gas token for these private actions. Pick a hosted deployment by environment name on the Supported chains page.