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This section provides an overview of the Wrap Lock / Token solution.

What Wrap Lock / Token does

The token bridging process starts with one blockchain having a predefined token (also called an asset) in it, with its own, preexisting, deployed and working eosio.token-compatible contract, which will be referred to as the native token in the context of the Wrap Lock / Token bridge.

The job of the Wrap Lock / Token bridge is then to allow users to transfer some quantity of these native tokens from an account that originally holds them on a source chain, to another beneficiary account on a destination chain. Once in the hands of the beneficiary in the destination chain, the tokens can move freely between accounts in the destination chain and, eventually, they should be able to return to their original chain, to any beneficiary accounts named in the return transfers.

The token bridge actually locks quantities of native tokens on the source chain, and mints a corresponting amount of the wrapped version of the tokens on the destination chain, to some specified beneficiary account. Some amount of the wrapped tokens can then later be submitted to the token bridge on the destination chain, which destroys these wrapped tokens, allowing the correspondign amount of locked native tokens to be released on the source chain to some specified beneficiary account.

Implementation overview

The Wrap Lock / Token solution is implemented as a pair of smart contracts: wraplock and wraptoken.

wraplock is deployed on what we will refer to in this documentation as the source chain, or chain A. It is where the native token contract, that is, the original token, resides, and is where the inter-blockchain token transfer begins.

wraptoken is deployed on what we will refer to in this documentation as the destination chain, or chain B. It is where the wrapped incarnation of the locked native token will be minted.

The wraplock and wraptoken contracts work together to facilitate interchain token transfers (also called wrapping and unwrapping). They require and utilise an IBC Bridge contract deployed on the blockchains at both ends of the tokens to be transferred. The bridge handles all the cryptographic proof verification that ensure native tokens are locked before wrapped tokens are minted, and that wrapped tokens are retired before native tokens are released.

Most actions in the wraplock and wraptoken API are straightforward, but note that the callers will need to supply IBC Bridge proof objects as parameters to the actions that actually operate the token transfers. These proof objects are used by Wrap Lock / Token to operate the IBC Bridge underlying it. The proof server supplied with the Antelope IBC suite is just one method for obtaining these proofs.

Token bridge setup overview

Wrap Lock / Token is modeled after and is compatible with the eosio.token standard, which allows one deployed token contract to have multiple assets (tokens) defined in it.

One deployed wraplock contract on chain A may handle interchain token transfers from any number of native token contracts, and any number of different assets issued on each one of these native token contracts. That means one wraplock contract on chain A may receive multiple transfers (deposits, for locking) of multiple assets (tokens) from multiple eosio.token-compatible token contracts on chain A.

One deployed wraptoken contract on chain B, on the other hand, corresponds to only one native token contract on chain A, but again any number of assets issued on it. This means that for every supported native token contract (not asset) on chain A that will be depositing tokens on a single wraplock contract on chain A, there will be one, exclusive, deployed instance of wraptoken on chain B to receive any and all assets from that supported native token contract on chain A.

Each wraplock and wraptoken contract is also restricted to moving tokens between two specific Antelope chains, considered the native and wrapped sides of the token bridge.

To facilitate transfers of both wrapped and native tokens in both directions, a pair of wraplock and wraptoken contracts needs to be deployed on both chains (this example is considering only one native token contract; see discussion above). In other words, if chain X is to have a full-duplex Wrap Lock / Token bridge to chain Y, then a wraplock contract on chain X is connected to a wraptoken contract on chain Y, and a wraplock contract on chain Y is connected to a wraptoken contract on chain X. Thus, native tokens on chain X can be sent to chain Y (where they incarnate as the wrapped version of these tokens), and native tokens on chain Y can also be sent to chain X.

And, to allow transfers across multiple chains, these (pairs of) contracts need to be deployed multiple times on a given chain: once per remote blockchain to connect to.