Overview

Introduction

Protocol v1 is MAP Protocol's light client-based cross-chain solution. It enables trustless cross-chain communication by verifying transactions through on-chain light clients, ensuring security based on the cryptographic proofs of source chains.

Design Goals

1. Trustless Verification: No trusted third party required for cross-chain verification

2. Cryptographic Security: Security derived from source chain consensus

3. Universal Compatibility: Support for both EVM and non-EVM chains

4. Decentralized Operation: Permissionless participation as Maintainer or Messenger

Architecture

┌─────────────────────────────────────────────────────────────────────────────┐
│                              Source Chain                                    │
│  ┌─────────────┐                                                            │
│  │   DApp      │──── Cross-chain Message ────┐                              │
│  └─────────────┘                             │                              │
│                                              ▼                              │
│  ┌─────────────────────────────────────────────────────────────────┐       │
│  │                    MOS Contract                                  │       │
│  │  - Emit cross-chain event                                        │       │
│  │  - Record message hash                                           │       │
│  └─────────────────────────────────────────────────────────────────┘       │
└─────────────────────────────────────────────────────────────────────────────┘
                                    │
                                    │  Maintainer monitors events
                                    │  Updates light client
                                    ▼
┌─────────────────────────────────────────────────────────────────────────────┐
│                            MAP Relay Chain                                   │
│  ┌─────────────────────────────────────────────────────────────────┐       │
│  │              Light Client (Source Chain)                         │       │
│  │  - Stores block headers                                          │       │
│  │  - Verifies Merkle proofs                                        │       │
│  └─────────────────────────────────────────────────────────────────┘       │
│                                                                             │
│  ┌─────────────────────────────────────────────────────────────────┐       │
│  │              Light Client (Target Chain)                         │       │
│  │  - Stores block headers                                          │       │
│  │  - Verifies Merkle proofs                                        │       │
│  └─────────────────────────────────────────────────────────────────┘       │
└─────────────────────────────────────────────────────────────────────────────┘
                                    │
                                    │  Messenger relays message
                                    │  with Merkle proof
                                    ▼
┌─────────────────────────────────────────────────────────────────────────────┐
│                              Target Chain                                    │
│  ┌─────────────────────────────────────────────────────────────────┐       │
│  │              Light Client (MAP Relay Chain)                      │       │
│  │  - Verifies proof from relay chain                               │       │
│  └─────────────────────────────────────────────────────────────────┘       │
│                                              │                              │
│                                              ▼                              │
│  ┌─────────────────────────────────────────────────────────────────┐       │
│  │                    MOS Contract                                  │       │
│  │  - Verify message proof                                          │       │
│  │  - Execute cross-chain call                                      │       │
│  └─────────────────────────────────────────────────────────────────┘       │
│                                              │                              │
│                                              ▼                              │
│  ┌─────────────┐                                                            │
│  │   DApp      │◄─── Cross-chain Message Delivered                          │
│  └─────────────┘                                                            │
└─────────────────────────────────────────────────────────────────────────────┘

Core Components

Light Client

Light clients are smart contracts deployed on each chain that maintain minimal state needed to verify transactions from other chains.

Functions:

• Store block headers (or validator set for PoS chains)

• Verify Merkle proofs

• Validate transaction inclusion

Implementations:

• MAPO Light Client (deployed on other chains)

• Other chain light clients (deployed on MAP Relay Chain)

MOS (MAP Omnichain Service)

MOS is the message passing layer that standardizes cross-chain communication.

Features:

• Unified message format

• Cross-chain event emission

• Message verification interface

Maintainer

Maintainers are off-chain services that keep light clients updated.

Responsibilities:

• Monitor source chain blocks

• Submit block headers to light clients

• Ensure light client state is current

Messenger

Messengers relay cross-chain messages between chains.

Responsibilities:

• Monitor cross-chain events

• Generate Merkle proofs

• Submit messages with proofs to target chains

• Earn fees for successful delivery

Cross-Chain Flow

Step 1: Message Initiation

1. User/DApp calls MOS contract on source chain

2. MOS contract emits cross-chain event

3. Event includes: target chain, target address, payload, fee

Step 2: Light Client Update

1. Maintainer detects new blocks on source chain

2. Maintainer submits block headers to light client on relay chain

3. Light client verifies and stores headers

Step 3: Message Relay

1. Messenger detects cross-chain event

2. Messenger generates Merkle proof for the event

3. Messenger submits message + proof to target chain

Step 4: Verification & Execution

1. Target chain MOS contract receives message

2. Light client verifies Merkle proof

3. If valid, MOS contract executes the cross-chain call

4. Target DApp receives the message

Security Model

Trust Assumptions

• Source chain consensus is secure

• Light client implementation is correct

• At least one honest Maintainer keeps light client updated

Attack Vectors & Mitigations

Attack	Mitigation
Fake block headers	Light client verifies consensus signatures
Invalid proofs	Merkle proof verification
Stale light client	Multiple independent Maintainers
Message replay	Nonce tracking in MOS contracts

Supported Chains

EVM Chains

• Ethereum

• BSC

• Polygon

• Arbitrum

• And more...

Non-EVM Chains

• Near Protocol

• (Others with light client implementation)

Limitations

1. Gas Costs: Proof verification can be expensive

2. Light Client Development: Requires implementation for each chain

3. Update Latency: Light client needs time to sync

4. No Bitcoin Support: Bitcoin lacks smart contract capability

Related Documentation

• Light Client Design

• MOS Architecture

• Chain Integration Guide