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This is CCTP V1 version. For the latest version, see CCTP.
This guide demonstrates how to use the viem framework and the CCTP V1 API in a simple script that enables a user to transfer USDC from a wallet address on the Ethereum Sepolia testnet to another wallet address on the Avalanche Fuji testnet. To get started with CCTP V1, follow the example script provided on GitHub. The example uses web3.js to transfer USDC from a wallet address on Ethereum Sepolia testnet to another wallet address on Avalanche Fuji testnet.
Interactive Tutorial with Developer ServicesIf you are new to building smart contracts, check out our interactive tutorial where you can transfer USDC using Circle’s Developer Services: Contracts and Wallets.
The script has five steps:
  1. In this first step, you initiate a transfer of USDC from one blockchain to another, and specify the recipient wallet address on the destination chain. This step approves the Ethereum Sepolia TokenMessenger contract to withdraw USDC from the provided Ethereum Sepolia wallet address.
Javascript
const approveTx = await usdcEthContract.methods
  .approve(ETH_TOKEN_MESSENGER_CONTRACT_ADDRESS, amount)
  .send({ gas: approveTxGas });
  1. In this second step, you facilitate a burn of the specified amount of USDC on the source chain. This step executes the depositForBurn function on the Ethereum Sepolia TokenMessenger contract deployed on Sepolia testnet.
Javascript
const burnTx = await ethTokenMessengerContract.methods
  .depositForBurn(
    amount,
    AVAX_DESTINATION_DOMAIN,
    destinationAddressInBytes32,
    USDC_ETH_CONTRACT_ADDRESS,
  )
  .send();
  1. In this third step, you make sure you have the correct message and hash it. This step extracts messageBytes emitted by the MessageSent event from depositForBurn transaction logs and hashes the retrieved messageBytes using the keccak256 hashing algorithm.
Javascript
const transactionReceipt = await web3.eth.getTransactionReceipt(
  burnTx.transactionHash,
);
const eventTopic = web3.utils.keccak256("MessageSent(bytes)");
const log = transactionReceipt.logs.find((l) => l.topics[0] === eventTopic);
const messageBytes = web3.eth.abi.decodeParameters(["bytes"], log.data)[0];
const messageHash = web3.utils.keccak256(messageBytes);
  1. In this fourth step, you request the attestation from Circle, which provides authorization to mint the specified amount of USDC on the destination chain. This step polls the attestation service to acquire the signature using the messageHash from the previous step.
Rate LimitThe attestation service rate limit is 35 requests per second. If you exceed 35 requests per second, the service blocks all API requests for the next 5 minutes and returns an HTTP 429 response.
Javascript
let attestationResponse = { status: "pending" };
while (attestationResponse.status != "complete") {
  const response = await fetch(
    `https://iris-api-sandbox.circle.com/attestations/${messageHash}`,
  );
  attestationResponse = await response.json();
  await new Promise((r) => setTimeout(r, 2000));
}
  1. In this final step, you enable USDC to be minted on the destination chain. This step calls the receiveMessage function on the Avalanche Fuji MessageTransmitter contract to receive USDC at the Avalanche Fuji wallet address.
Javascript
const receiveTx = await avaxMessageTransmitterContract.receiveMessage(
  receivingMessageBytes,
  signature,
);
You have successfully transferred USDC between two EVM-compatible chains using CCTP V1 end-to-end!
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