ZRC-20 on ZetaChain
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.
Summary
Native gas tokens of connected blockchains and whitelisted ERC-20 tokens can be deposited to ZetaChain as ZRC-20 tokens. During the deposit process, the native/ERC-20 tokens are transferred to and locked in the TSS address/ERC-20 custody contract and ZRC-20 tokens are minted on ZetaChain and deposited to the recipient address.
ZRC-20 tokens can be withdrawn from ZetaChain to connected blockchains. During the withdrawal process, ZRC-20 tokens are burnt on ZetaChain and native/ERC-20 tokens are transferred to the recipient address on the connected chain from a TSS address/ERC-20 custody contract.
ZRC-20 tokens can only be minted by the ZetaChain protocol. An ERC-20 token deployed on ZetaChain does not have the properties of ZRC-20 and can't be withdrawn from ZetaChain to a connected chain.
The "same" ERC-20 token from two connected blockchains is represented as two different ZRC-20 tokens on ZetaChain. For example, USDT from Ethereum is represented as ZRC-20 USDT from Ethereum, and USDT from BSC is represented as ZRC-20 USDT from BSC. They are not considered the same asset by ZetaChain, but they can be swapped. That's how the transfer of the "same" ERC-20 asset can be implemented on ZetaChain: by depositing an ERC-20 (chain A), swapping this ZRC-20 (chain A) to an ZRC-20 (chain B), and withdrawing the ZRC-20 (chain B) to chain B as ERC-20.
Supported Assets
A list of currently supported assets:
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 (opens in a new tab) 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 (opens in a new tab)).
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 sETH, 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
.
When depositing native gas tokens from EVM-based connected chains, there is no additional cross-chain fee. If you send 1 token to a TSS address, you will receive 1 ZRC-20 version of the same token on ZetaChain.
For Bitcoin deposits, which utilize the UTXO (Unspent Transaction Output) model, the process incurs additional fees.
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 theonCrossChainCall
function of that contract will be called with themessage
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 theonCrossChainCall
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.
Block Confirmations
When depositing to or withdrawing from ZetaChain, the protocol requires a certain number of confirmations on the connected chain before the transaction is considered final. The number of confirmations required is different for each chain. You can check the number of confirmations in the table below:
These values are stored in the state of ZetaChain and are used by ZetaClient (the program that observer-signer validators run) as recommended values of confirmations. In some cases ZetaClient can use a higher number of confirmations, for example, when the value transfer exceeds a specified amount.
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 connected chains will be returned to the sender. You can view the caps on the explorer here (opens in a new tab).
Continue Learning
Continue with the next part or try a related tutorial