Connecting Chains: From PFM to PMF & ICA as Router

Introduction

In the evolving landscape of blockchain Interoperability, connecting different chains efficiently and securely is crucial. This document explores the current status quo of inter-chain communication, its limitations, and proposes advanced concepts like Packet-Forward Middleware (PMF) and Ideal ICA as potential routers for improved chain connections.

Packet-Forward Middleware and Its Limitations

Union, in its most basic form, is a decentralized general message passing interoperability chain [1]. The current method of relaying transfers through Union uses Packet-Forward Middleware (PFM). However, PFM has several limitations that hinder its effectiveness in complex blockchain ecosystems.

Basic Flow of Union's Interoperability

1. Chain A sends a transfer request to Union.

2. Union passes this request along to Chain C.

3. Chain C receives this request and assumes it's valid because it trusts Union.

Limitations of Packet-Forward Middleware (PFM)

1. Transfers-only: PFM is primarily designed to handle IBC transfers [2], focusing on moving tokens or assets between different blockchains. It doesn't handle non-transfer packets, limiting its utility for other types of inter-chain communication like governance proposals or complex smart contract interactions.

2. Alteration of Original Transfers: PFM strips the forwarding information from the original IBC transfer on Union and creates a new transfer. This alteration of the original packet data changes the merkle inclusion proof, making it difficult to audit or trace transactions back to their origin, especially on-chain. Example of transfer alteration:

   jsonCopyChain A → Union Transfer:
   {
     sender: Karel
     recipient: PFM
     amount: 10
     extension: {
       forward: {
         port: 1,
         channel: 3,
         recipient: Robert
       }
     }
   }
   
   Union → Chain C (after PFM rewrites) Transfer:
   {
     sender: Karel
     recipient: Robert
     amount: 10
   }

3. Complex Routing Limitations: PFM creates new transactions with new sequence numbers when forwarding packets, disrupting the continuity of transaction history. This complicates scenarios requiring precise order tracking across multiple chains, such as complex routing with specific execution instructions.

These limitations highlight the need for more advanced and flexible solutions in connecting chains, which leads us to explore concepts like PMF and ICA as potential routers.

Interchain Accounts (ICA) as a Router

ICA represent a significant advancement in blockchain Interoperability, offering solutions to many limitations faced by simpler methods like PFM.

Understanding Interchain Accounts

Interchain Accounts are a feature of the Inter-Blockchain Communication (IBC) protocol that allows one blockchain (the controller chain) to control an account on another blockchain (the host chain). This creates a powerful mechanism for cross-chain interactions and routing.

ICA Functioning as an EOA

In the context of Union chain interoperability, an Interchain Account functions similarly to an EOA, but with some key differences:

1. Cross-Chain Control: Unlike a typical EOA which is controlled by a private key, an ICA is controlled by another blockchain through IBC.

2. Message Forwarding: The ICA can receive messages from its controller chain and execute them on the host chain.

3. Nested Message Structure: It can handle complex, nested message structures, allowing for sophisticated routing scenarios.

Nested Message Structure (Russian Doll Concept)

The ICA's ability to handle nested messages can be likened to a Matryoshka doll (Russian nesting doll). This structure allows for encapsulating routing information within the message itself:

jsonCopy{
  "sender": "Karel",
  "recipient": "ICA on Union",
  "message": {
    "message": {
      "port": "1",
      "channel": "3",
      "recipient": "Chain C"
    }
  }
}

In this structure:

• The outer layer contains the information for routing to the ICA on Union.

• The inner layer contains the information for routing from Union to the final destination (Chain C).