Ion Stage 1 Smart Contracts

Ion Lock walkthrough Smart Contracts used.

Core

The contracts below are the two main contracts being interacted with.

IonLink.sol

Implements IonLinkInterface. Maintains latest merkle root to be verified against a proof given to the withdraw function in ERC223. It is made of two functions: Update( uint256 _new_block_root ) which updates the latest merkle root, and Verify( uint256 block_id, uint256 leaf_hash, uint256[] proof ) which verifies is a proof and leaf given correspond to a merkle tree root submitted at the block id given.

It receives new roots from our Lithium service but any intermediary can submit these roots. The roots submitted must be generated for leaves that have the structure that is defined in IonLock.

IonLock.sol

Implements ERC223ReceivingContract. Allows withdraws through Withdraw( uint256 _value, bytes32 _ref, uint256 _block_id, uint256[] _proof ). When a withdraw is made the the proof given is verified against IonLink.

The proof is an array of hashes that is a path to the leaf being verified. The leaf hash must be in the format H(address_of_withdraw_beneficiary, token_contract_address, ionlock_contract_address, amount_of_tokens, H(payment_reference_of_opposite_deposit)) where H() is the keccak256 hashing function.

Helpers

The contracts below are either libraries or interfaces used by the core contracts or are additional helper contracts required for the stack to function and are replaceable by custom contracts.

ECVerify.sol library

A safer ecrecovery(bytes32 hash, bytes sig) implementation.

ERC223.sol interface

Describes the ERC223 Token standard.

ERC223Compatible.sol interface

Describes the ERC223ReceivingContract interface. The ERC223ReceivingContract defines how tokenFallback(address _from, uint _value, bytes _data) should look in order to implement contracts that are able to receive tokens.

IonCompatible.sol interface

Describes IonLinkInterface and IonCompatible. IonCompatible describes interface for multiple events to be triggered in order for Lithium (externally) to catch them. IonLinkInterface interface (describing the verify function).