Aion has distinguished itself as a protocol-layer smart contract and dApp platform that is faster and cheaper than Ethereum, is Solidity-compatible, and recently released a Java-based virtual machine that promises further advancements in speed, efficiency, and developer toolsets.

All of Aion’s technical achievements over the last year are noteworthy, but Aion is chiefly known as a blockchain interoperability project. This article aims to highlight Aion’s interoperability milestones to date and break down its latest code release — the Transwarp Conduit.

Token Bridge and Swap

The AION cryptocurrency began as an ERC-20 token on Ethereum in late 2017. Aion’s proof-of-work main net went live on April 25, 2018, but the only “native” AION coins at the time were the block rewards earned by the miners securing the network. In order to fully realize the crypto-economic system envisioned in Aion’s white papers, in September 2018 Aion began the process of migrating and converting the Aion ERC-20 token supply to native AION coins. Many tokens were automatically converted by exchanges, but Aion also facilitated the swap using its unique decentralized token bridge.

Aion ERC-20 holders could use the token bridge user interface to enter their destination native AION address and the amount of Aion ERC-20 tokens they wished to swap. The interface would then generate smart contract data to be executed. A group of nodes connected to both Ethereum and Aion’s main nets would confirm the transaction on each network, burn the Aion ERC-20 tokens on Ethereum, and transfer an equal number of native AION coins to the destination address on Aion.

Over 100,000,000 Aion ERC-20 tokens were converted to native AION coins through the bridge (over $11,000,000 in value). Aion’s token swap was one of the most engaged ever, achieving an over-97% participation rate.

The token bridge was Aion’s first example of interoperability in action. The source code is available on Aion’s GitHub.

Aion Token Standard and Bidirectional Bridging

The original token bridge was designed as a one-way conversion from the Aion ERC-20 to the native AION coin. The Aion team recognized that interchain tokens could unlock previously-unrealized opportunities for value transfer and utility between different blockchains. This would require a system that could securely facilitate the movement of tokens between different blockchains while maintaining a stable total supply.

Aion’s solution requires two main components: an interoperable token and a bridge to facilitate bidirectional transfers.

Diagram of interchain value transfer contract architecture

Aion developed a unique token standard with built-in interoperability functions (“AIP-4” or “ATS” tokens). This standard is derived from Ethereum’s ERC-777 standard but features unique “freeze”, “thaw”, and “liquidSupply” functions. The “freeze” function holds the tokens in the ATS contract on the home chain while the bridge contract “thaws” an equal number of tokens on the remote chain. The “liquidSupply” function tracks the number of frozen and thawed tokens to ensure that the total supply remains stable between the home and remote chains. Aion wrote a guide for how to create your own ATS token contract and deploy it on the network.

Aion passed the torch to its enterprise development partner, MavenNet, to expand on the one-way token bridge blueprint by making it bidirectional. The bridge operator standard is already published on Github and MavenNet has a demo video available. The production release is pending user interface packaging.

Aion’s Transwarp Conduit

Aion calls its latest code release the Transwarp Conduit (“TWC”). The details are laid out in Aion’s TWC blog post, white paper, and GitHub. In essence, the TWC enables the transfer of arbitrary messages between different blockchains. This unlocks the ability for developers to create interchain smart contracts and dApps.

Aion’s GitHub provides an overview of the process:

The TWC bridge node connects two blockchains by listening to the source chain’s Adapter contract events and calling the destination adapter. Users can call the Adapter contract either through a smart contract or an application with the message details to be transferred. TWC node will pick up this event and ask signatories to attest to its history and content. Once enough signatures have been collected, the transfer transaction will be submitted to the destination Adapter where it will be validated. If the transfer is valid, it will be processed by the contract and the encoded function will be called.

How it works (ELI5 version):

You want to send a package (call a smart contract function) to a friend overseas (dApp on another blockchain). You wrap it in a box (metadata header, like the TCP/IP datagram format) with your friend’s address, your return address, postage (transaction fee), and weight (message hash) and get a time-stamped delivery slip (source chain transaction hash). The local post office (adapter contract) checks the postage and puts the box in the delivery queue. The delivery person (TWC node linked to both chains) picks up the box and asks a group of supervisors (signatories) to double check the box and the delivery slip to make sure it is the right box and hasn’t been tampered with. Once the delivery person has enough supervisor signatures, she transports the box to the overseas office (adapter contract on the destination chain). The overseas office checks that the supervisor signatures are valid before finally delivering the box to your friend (executing the smart contract call) and noting the box as delivered.

Aion acknowledges that this is not a “perfect” solution (if such a thing is even possible). Some decentralization is sacrificed in that the destination adapter contract determines which TWC node and signatory addresses will be considered valid. Additionally, as with any system for interchain transactions, 51% attacks and forks on either the source or destination blockchain can have an impact on both chains when an interchain transaction is affected. The TWC white paper includes precautionary recommendations for interchain smart contract developers about how to minimize risks and handle issues if they arise. Aion describes the TWC as a starting point they intend to continue building upon.

Aion’s TWC is compelling for three reasons:

It can transfer messages between any two blockchains that support user-defined smart contract functions and signature validation.

The process is auditable from start to finish because every step is completed on-chain.

The content of the message can be anything, including smart contract function calls and logical arguments.

No vendor lock-in. No black box. Unlimited possibilities.

So What?

Interchain value transfer and dApps open the door to blockchain use cases that were never before possible. The most obvious is a multi-blockchain decentralized exchange, where users do not need to rely on a centralized intermediary to take custody of their cryptocurrency and execute trades off-chain. However, that barely scratches the surface of the potential applications that Aion’s vision for blockchain interoperability offers:

Integrate data from enterprise blockchains and off-chain data oracles in supply chain systems and trigger payments on a public blockchain upon confirmation of delivery;

Use digital identity information to open blockchain-based savings and loan accounts;

Automatically coordinate healthcare services and insurance payments;

And much more yet to be imagined and built.

The interoperability milestones Aion has reached are still early steps on a much longer development roadmap. Aion’s progress to date demonstrates a commitment to execution, innovation, and engineering excellence.