Proxies

We already know that ISMP mimics the HTTP API, in terms of requests and responses, using POST requests to send data and GET requests for cross-chain state reads. It also allows for request and response proxies, akin to a typical HTTP proxy. An ISMP proxy simply redirects incoming requests and responses to an external state machine.

In this context, the proxy functions as a coprocessor. Without it, the state machine would have to independently verify its consensus and state proofs of an incoming request. This verification could be prohibitively expensive. For instance, if a single state machine had to verify consensus proofs for all state machines it receives requests from, it would significantly increase the cost of interoperability. This highlights the value of a proxy state machine, intentionally designed to be inexpensive to verify. It proxies requests by carrying out the costly verification computations on its chain, and providing cheaper proofs for its consumer chains. Proxies enable more efficient cross-chain communication by reducing the cost of verifying multiple interoperability proofs, freeing up valuable blockspace for other applications.

A blockchain may configure any of its connected state machines on the IsmpHost as a proxy. If a state machine is not configured as a proxy, then any requests from this chain must have their source matching it's state machine identifier. This protocol invariant must be maintained for the security of modules that use the request metadata for message authentication.

Hyperbridge as a Proxy

Hyperbridge serves as an instance of an ISMP proxy, aggregating the consensus proofs and messages from all its connected chains. This allows any chain to receive all of its intended messages directly from Hyperbridge through a single consensus proof. Hyperbridge is fully decentralized and governed by its own token, without any privileged actors with superuser permissions. This level of decentralization is only achievable as a Polkadot parachain with decentralized on-chain governance, permissionless block producers, and forkless upgrades that facilitate the support for new chains.