> ## Documentation Index
> Fetch the complete documentation index at: https://developers.circle.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Cross-Chain Transfer Protocol V1

> Move USDC securely across blockchains and simplify user experience

<Warning>
  **This is CCTP V1 (Legacy) version. For the latest version, see [CCTP](/cctp)**.
</Warning>

## Overview

**Cross-Chain Transfer Protocol V1** is a permissionless onchain utility that
facilitates USDC transfers securely between blockchain networks via native
burning and minting. Circle created CCTP to improve capital efficiency and
minimize trust requirements when using USDC across blockchain networks. CCTP V1
enables developers to build multichain applications that allow users to perform
1:1 transfers of USDC securely across blockchains.

<Note>
  **Note:** CCTP V1 only supports **Standard Transfer**, constrained by
  blockchain finality on the source blockchain. Later [CCTP](/cctp) versions
  support **Fast Transfer** and **Hooks**, in addition to also supporting
  **Standard Transfer**.
</Note>

## Understanding the Problem

Blockchain networks often operate in siloed environments and cannot natively
communicate with one another. While some ecosystems, such as Cosmos, use
built-in protocols like the Inter-Blockchain Communication (IBC) protocol to
enable data transmission between their appchains, direct communication between
isolated networks, such as Ethereum and Avalanche, remains infeasible.

Traditional bridges exist to address this limitation by enabling the transfer of
digital assets, such as USDC, across blockchains. However, these bridges come
with significant drawbacks. Two common methods, lock-and-mint bridging and
liquidity pool bridging, require locking USDC liquidity in third-party smart
contracts. This approach reduces capital efficiency and introduces additional
trust assumptions.

## Design Approach

As a low-level primitive, CCTP V1 can be embedded within any app or wallet -
even existing bridges - to enhance and simplify the user experience for
cross-chain use cases. With USDC circulating across a large number of blockchain
networks, CCTP V1 can connect and unify liquidity across disparate ecosystems
where it's supported.

CCTP V1 is built on generalized message passing and designed for composability,
enabling a wide range of use cases. Developers can extend its functionality
beyond just moving USDC between blockchains. For example, you can create a flow
where USDC is sent across chains and automatically deposited into a DeFi lending
pool after the transfer, allowing it to generate yield in an automated manner.
This experience can be designed to feel like a seamless, single transaction for
the end user.

## How CCTP V1 works

**Standard Transfer** is the default method in CCTP V1 for transferring USDC
across blockchains, which involves burning USDC on the source chain and minting
it on the destination chain. It relies on transaction finality on the source
chain and uses Circle's Attestation Service to enable standard-finality
(<Tooltip tip="The point at which a transaction is fully finalized on-chain and can no longer be reversed or reorganized. This ensures the highest level of security and certainty before attestation. Hard Finality requires the transaction to reach full consensus on the source blockchain, typically resulting in longer processing times.">hard
finality</Tooltip>) transfers. The process includes the following steps:

1. **Initiation**. A user accesses an app powered by CCTP V1 and initiates a
   Standard Transfer of USDC, specifying the recipient's wallet address on the
   destination chain.
2. **Burn Event**. The app facilitates a burn of the specified USDC amount on
   the source blockchain.
3. **Attestation**. Circle's Attestation Service observes the burn event and,
   after observing hard finality on the source chain, issues a signed
   attestation. Hard finality ensures the burn is irreversible (about 13 to 19
   minutes for Ethereum and L2 chains.)
4. **Mint Event**. The app retrieves the signed attestation from Circle and uses
   it to mint USDC on the destination chain.
5. **Completion**. The recipient wallet address receives the newly minted USDC
   on the destination blockchain, completing the transfer.

**Standard Transfer** prioritizes reliability and security, making it suitable
for scenarios where finality wait times are acceptable.

## Use Cases

CCTP V1 enables developers to build novel cross-chain apps that integrate
functionalities like trading, lending, payments, NFTs, and gaming, while
simplifying the user experience. Below are some practical examples of how you
can leverage CCTP V1 in your applications, either directly or indirectly by
routing USDC behind the scenes:

### Cross-chain rebalancing

Market makers, fillers/solvers, exchanges, and bridges can use CCTP V1 to manage
liquidity more efficiently. By securely rebalancing USDC holdings across
blockchains, you can reduce operational costs, meet demand, and take advantage
of market opportunities with minimal latency.

### Cross-chain swaps

With CCTP V1, users can quickly swap between digital assets on different
blockchains by routing through USDC. Users can also swap for USDC and
automatically trigger subsequent actions on the destination chain, enabling
seamless cross-chain transactions.

### Cross-chain purchases

Automate cross-chain purchases with CCTP V1. For example, a user can use USDC on
one chain to purchase an NFT on a decentralized exchange on another chain and
list it for sale on an NFT marketplace. When the transaction is initiated, CCTP
V1 routes USDC across chains to buy the NFT and opens the listing on the
marketplace—all in one streamlined flow.

### Simplify cross-chain complexities

Simplify the cross-chain experience by using USDC as collateral on one chain to
open a borrowing position on a lending protocol on another chain. With CCTP V1,
USDC can move quickly between blockchains, allowing users to onboard to new
applications without switching wallets or managing multi-chain complexities.