10. Smartbridge Technology

10.1 The Need to Interoperate

The ARK SmartBridge solution addresses a major issue that hinders the adoption of blockchain technology: the isolation of individual main networks. Currently, interoperability is largely controlled by central exchanges that oversee asset transfer. ARK, in contrast, allows data and asset transfer without the need for custodial third parties.

Two protocols define SmartBridge communication:

Protocol-Specific SmartBridge. This represents communication between various chains based on ARK Core technology that operate within the ARK Ecosystem network of bridgechains. This is also known as bridgechain communication.

Protocol-Agnostic Smartbridge. This represents communication between blockchains that use different consensus mechanisms, tokens and protocols, for example Bitcoin and others. This is also known as cross-chain communication.

10.2 ARK-ARK SmartBridge Mechanics

Protocol-Specific SmartBridge refers to a communication layer targeting ARK-based application-centric blockchains. In addition to standard token swaps, communication across bridgechains will enable both bridgechain validation and the ability to exchange both data and information. Protocol realization was recently made possible with the release of the brand new Core v2, and by expanding functions supported by ARK Logic.

The bridgechain protocol will operate via core-bridge, a module that operates in tandem with the new bridgechain registration transaction type that carries proof of trust/ownership of the originator of the registration transaction. Bridgechain registration means that any new bridgechain will need to be registered via our mainnet. The ARK Public Network will act as a proxy, main highway, and decentralized guard for interchain communication.

ARK has been upgraded for event triggering with the use of webhooks and basic event emitters. Events are used inside the Core to trigger blockchain actions and the delivery of webhook payloads. Additionally, custom plugins can utilize the event emitter package to trigger their own actions in response to blockchain events. Conceptually, this feature is similar to the Hooks implementation in WordPress [49], as well as the lifecycle hook access provided by JavaScript frameworks such as Vue and React [50] [51].

Due to the need for strict protocols around blockchain data creation and retrieval, events are strictly reactionary. Core events are not capable of changing data at runtime. The transaction applied event, for instance, passes a complete transaction instance, not raw transaction data that can be altered in the style of a WordPress filter. Another way to represent the event API is in the context of a publish-subscribe pattern [52]. In this pattern, ARK Core packages can act both as publishers and subscribers of events.

Bridgechain protocol transactions enabling coin transfers will need to be confirmed on three levels: the sending blockchain, ARK mainnet, and the receiving blockchain. The bridgechain protocol logic will be replicable, meaning that any bridgechain is able to act as a self-governing mainnet, thus making a horizontal connection through the web of blockchains and enabling exit via ARK mainnet.

10.3 ARK-ANY Smartbridge Mechanics

A community project called ARK Contract Execution Services (ACES) has demonstrated two-way transfers between ARK and Bitcoin, Litecoin, and Ethereum, including issuing smart contracts from ARK to Ethereum, regardless of the underlying protocols. ACES can adapt to any blockchain as needed [54].

Communication takes place through a special data section called vendor fields. At 255 characters, each transaction can be used to send text, instructions or code. This can also be used for hashing functions or even to trigger events such as smart contracts on other blockchains.

Intermediary nodes known as encoded listeners comb through this data for tasks to perform. These encoded listeners can be programmed and run however the operator sees fit, including running an exchange pool similar to ShapeShift or Changelly. Competing encoded listener node runners can launch ACES nodes for various coins, creating an encoded listener marketplace [48].

ACES is not a fully decentralized solution, even though it can result in multiple interaction points between two chains that are independently operated, providing redundancy. It is worth noting, however, that aside from handling other blockchains, ACES can also handle communication between ARK-based chains. ACES can be used while the decentralized SmartBridge Technology between various ARK-based blockchains is developed, and other blockchains or tokens that wish to migrate to ARK can do so via ACES token bridge. ACES is currently undergoing upgrades following the ARK Core redesign, and aspects of the ACES approach are now integrated into the Core itself. An example of this approach that uses the plugin/module implementation is the ARK and HyperLedger Fabric integration. The plugin-enabled execution of HyperLedger SmartContracts functions via ARK SmartBridge by using the vendor field as an interface [53].

Following the release of ARK v2, the immediate focus of the team is on building the ecosystem and optimizing interchain among ARK-based blockchains. Subsequent efforts will develop Protocol-Agnostic Smartbridge.