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Omnichain Contracts
ZRC-20 Tokens

ZRC-20

ZRC-20 is a token standard integrated into ZetaChain's omnichain smart contract platform. With ZRC-20, developers can build dApps that orchestrate native assets on any connected chain. This makes building Omnichain DeFi protocols and dApps such as Omnichain DEXs, Omnichain Lending, Omnichain Portfolio Management, and anything else that involves fungible tokens on multiple chains from a single place extremely simple — as if they were all on a single chain.

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Supported Assets​

A list of currently supported assets is stored on-chain:

New assets can be added or removed by broadcasting a transaction with a corresponding message of the fungible module on ZetaChain.

Introduction​

At a high-level, ZRC-20 tokens are an extension of the standard ERC-20 tokens found in the Ethereum ecosystem, ZRC-20 tokens have the added ability to manage assets on all ZetaChain-connected chains. Any fungible token, including Bitcoin, ETH, other gas assets and ERC-20-equivalents on other chains, may be represented on ZetaChain as a ZRC-20 and orchestrated as if it were any other fungible token (like an ERC-20).

Interface​

ZRC-20 is based on ERC-20, with three additional functions and some associated events for integration with Cross-Chain Transactions (CCTXs) in ZetaChain (see the IZRC20 interface).

Comparing ZRC-20 to ERC-20, there are additional external functions to deposit and withdraw, and additional events for each of them. This makes ZRC-20 completely compatible with any applications built for ERC-20s, but with an extremely simple interface to also function in an omnichain way.

Depositing Native Gas Tokens as ZRC-20​

To deposit a native gas token (like gETH, tMATIC, tBNB, or tBTC) to ZetaChain, send it to the TSS address on a connected chain.

If the input data field of the transaction is empty, the token will be deposited to the sender's address on ZetaChain.

If the input data field is not empty, the protocol looks up the first 20 bytes of the input data field. If the first 20 bytes correspond to an EOA address on ZetaChain, the token will be deposited to that address. If the first 20 bytes correspond to a contract address on ZetaChain, the token will be deposited to that contract and the onCrossChainCall function of that contract will be called with the remaining input data as the message.

Depositing Supported ERC-20 Tokens as ZRC-20​

To deposit a supported ERC-20 token to ZetaChain, use the deposit method of the ERC-20 custody contract on a connected chain.

The deposit method accepts the following parameters:

  • recipient: the address on ZetaChain to deposit the tokens to. If the recipient is an EOA, the tokens will be deposited to the recipient's address. If the recipient is a contract, the tokens will be deposited to the contract and the onCrossChainCall function of that contract will be called with the message as an argument.
  • asset: the address of the ERC-20 token to deposit.
  • amount: the amount of tokens to deposit.
  • message: an arbitrary message to be passed to the onCrossChainCall function of the recipient contract. If the recipient is an EOA, the message should be empty.

Withdrawing ZRC-20 Tokens from ZetaChain​

ZRC-20 tokens, which include those representing native gas tokens as well as ERC-20 tokens, can be withdrawn from ZetaChain by calling the withdraw method on the ZRC-20 contract.

This method burns the tokens and emits a Withdrawal event. This event will trigger a CCTX from ZetaChain to the connected chain from which the token was deposited. After the CCTX is processed the token amount will be transferred to the recipient address on the connected chain either from a TSS address (for native gas tokens) or from the ERC-20 custody contract (for ERC-20 tokens).

Check out the Swap tutorial to learn how to build omnichain contracts that accept token deposits form connected chains, swap between ZRC-20 tokens using the internal liquidity pools on ZetaChain, and withdraw them to connected chains.

Liquidity Cap​

Each ZRC-20 has a total cap on the number of deposited tokens that the protocol can accept. Any assets beyond this deposited to ZetaChain from external chains will be returned to the sender. You can view the caps on the explorer here.