# ERC-20 Bridge

Anyone can build on top of the warp.green protocol. At launch, we provided two simple example applications, one of which is called the ERC-20 bridge. As the name suggests, it allows wrapping and unwrapping ERC-20s on Chia by converting them to equivalent CATs. The contracts can be found [here](https://github.com/warpdotgreen/cli/tree/master/contracts).

<figure><img src="https://2092748345-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fh8reaKqot1wdAxt5Fpnq%2Fuploads%2Fculjppke5UZbgOt7CSCo%2Fimage.png?alt=media&#x26;token=b10ece3a-9460-4a20-adf3-2abd6397a3df" alt=""><figcaption><p>The two apps presented in the docs, ERC-20 Bridge and CAT Bridge, are fully immutable apps. They use the warp.green cross-chain messaging protocol as an oracle, meaning that they trust the protocol to relay truthful data. </p></figcaption></figure>

<figure><img src="https://2092748345-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fh8reaKqot1wdAxt5Fpnq%2Fuploads%2F7yuPdPLM2xsXLpzuWu2w%2Fimage.png?alt=media&#x26;token=22463888-fc9d-40ef-ac05-1cca2c9446f0" alt=""><figcaption><p>ERC20Bridge.sol overview - While it trusts an oracle to be truthful, the contract itself is immutable once deployed and initialized. No account has any specific privileges - ERC-20 tokens are owned by the contract until unwrapped.  </p></figcaption></figure>

### Message Contents

As previously mentioned, each message sent through the warp.green protocol has a contents field which consists of 32-byte values. In the case of `ERC20Bridge`, the contents array contains 3 elements:

* **ERC-20 Contract Address**: The contract address of the token being wrapped, which is essentially used as an identifier
* **Receiver**: The address that will receive either the wrapped ERC-20 CATs (when wrapping) or original ERC-20 tokens (when unwrapping).  This value is either a puzzle hash (when wrapping) or an address (when unwrapping).
* **Amount in mojos**: Amount, in mojos, of wrapped CATs to be minted or that have been burned.

Note that all values are automatically padded with leading 0s to be 32-byte.